The next generation of large ground based astronomical telescopes will have their primary mirrors, and in some cases secondary mirrors, built using a segmented approach. Corning has the capacity and capability to produce mirror segment blanks from Corning ULEThe next generation of large ground based astronomical telescopes will have their primary mirrors, and in some cases secondary mirrors, built using a segmented approach. Corning has the capacity and capability to produce mirror segment blanks from Corning ULE^® titania-silica glass in segment sizes ranging from 1.0- meter to 1.8-meters flat to flat (1.2-meter to 2.1-meter point to point). Corning also has the capability of producing large monolithic mirrors for use in secondary, tertiary and/or other mirror blanks up to 8.5-meters in diameter. This paper will review and further discuss the material and processes employed by Corning to produce several hundred to several thousand mirror segment blanks for extremely large telescopes, along with large monolithic mirror blanks for downstream optics, titania-silica glass in segment sizes ranging from 1.0- meter to 1.8-meters flat to flat (1.2-meter to 2.1-meter point to point). Corning also has the capability of producing large monolithic mirrors for use in secondary, tertiary and/or other mirror blanks up to 8.5-meters in diameter. This paper will review and further discuss the material and processes employed by Corning to produce several hundred to several thousand mirror segment blanks for extremely large telescopes, along with large monolithic mirror blanks for downstream optics.

Ultra-Low Expansion (ULE^®) glass has been and continues to be a significant material for astronomical applications. With a nominal composition of 7 wt. %TiO₂ in SiO₂, Corning Code 7972 ULE^® has a mean room temperature coefficient of thermal expansion (CTE) of 0 ± 30 ppb/°C with a typical CTE range of less than 15 ppb/°C, properties vital to the manufacture of high resolution optics requiring extreme thermal stability. Combined with lightweighting techniques developed at Corning during the past 30 years, ULE^® has been successfully employed for numerous monolithic and lightweight mirror applications including the 2.4 meter Hubble Space Telescope lightweight primary mirror, the Airborne Laser (ABL) primary mirrors, and most recently the Discovery Channel Telescope 4 meter mirror blank. ULE^® maintains its strong candidacy for future ELT applications. Recent challenges in mirror surface specifications and the development of alternative material choices calls for a comparison with ULE^®. The objective of this article is to review ULE^® properties and manufacturing capabilities, and to compare relevant material properties to those of alternative material options, thus allowing designers to properly execute material selection. Finally, recent development efforts directed toward improving ULE^® will be discussed.

ECM investigated in the past three years the repeatability and reproducibility of Cesic^® for a serial production of optical applications. Under ESO - European Southern Observatory - contract ECM performed also a feasibility study for the manufacturing of Cesic^® primary and secondary mirror segments for the Overwhelmingly Large (OWL) Telescope. The main issues of this study were (1) to develop a new manufacturing process suitable for the serial production of the OWL Cesic^® mirror segments (~2550), including the polishable surface (but not the polishing itself), that greatly reduces cost and schedule compared to traditional manufacturing; and (2) to design a manufacturing facility that optimises the new manufacturing process.

In May, 2000 the MMT Conversion was dedicated. Space limitations on the summit of Mt. Hopkins, AZ and limited financial resources dictated in-situ aluminization of the φ 6.5m primary mirror. Some of the attendant challenges successfully addressed in the course of accomplishing that task are described. For example: a 22 metric ton, φ7m vacuum head had to be lifted 25m before being lowered through the horizon-pointing telescope truss (clearing by 16 mm), then secured to the mirror cell that serves as a vacuum vessel; dirty mirror-support hardware integral to the cell required isolation of the process volume operating at 10^-6mbar; extensive modeling of source geometry was needed to achieve uniformity goals at very short source-substrate distances; and a cost-effective 75kW DC filament voltage source using commercially-available arc welders was developed that allowed simultaneous firing of 200 evaporation sources. Details of design and construction of the evaporation system are given along with techniques and results of the successful coating in November 2001 and September 2005.

For future extremely large telescope projects like OWL or TMT with at least several hundreds of mirror blanks the homogeneity of the coefficient of linear thermal expansion (CTE) within a single blank is an important issue. The telescope designers are not only interested in the global CTE homogeneity but also in measuring the axial CTE gradient to the highest precision. It has been proven in the past in many projects like GTC and Keck that ZERODUR(r) itself is a material of highest homogeneity even in large dimensions and huge quantities. About 95.5% of all 2m class mirror segments of all projects exhibit a peak to valley homogeneity of better than 0.015*10^-6K^-1. The actual homogeneity of the material is even better because the results so far are largely influenced by the restrictions of the CTE measurement repeatability in the past. This paper introduces an advanced method for the measurement of the CTE of ZERODUR(r) exhibiting a significantly improved reproducibility. The dilatometer setup was especially optimized to cope with the demand of highly accurate homogeneity measurements of 2 m class ZERODUR(r) segments for giant astronomical telescopes. Detailed measurement results out of a single 1.5 m class ZERODUR(r) segment based on the current state of production will be shown. The results show CTE distributions in radial, angular and axial direction. SCHOTT has already improved the production capacity for ZERODUR(r) immensely, thereby the results represent the current status of quality of the available mass production facilities at SCHOTT.

This paper is intended to establish, after delivery of the last batch of segments, the final progress report of the manufacturing and testing of the Gran Telescopio Canarias optics.

An ultra precision large optics grinder, which will provide a rapid and economic solution for grinding large off-axis aspherical and free-form optical components, has been developed at Cranfield University. This paper presents representative grinding experiments performed on another machine - a 5 axes Edgetek - in order to verify the proposed BoX(r) grinding cycle. The optical materials assessed included; Zerodur(r), SIC and ULE(r), all three being materials are candidates for extreme large telescope (ELT) mirror segments. Investigated removal rates ranged from 2mm³/s to 200mm³/s. The higher removal rate ensures that a 1 metre size optic could be ground in less than 10 hours. These experiments point out the effect of diamond grit size on the surface quality and wheel wear. The power and forces for each material type at differing removal rates are presented, together with subsurface damage.

The requirements of space and defence optical systems and ground-based astronomy (especially extremely large telescopes) are providing optical fabricators with new challenges. These challenges particularly concern process speed, determinism and automation, and tighter tolerances on surface form and texture. Moreover, there is a growing demand for complex off-axis and 'freeform' surfaces and for larger components of the ~1m scale. With this in view, we first report on form-correction on a smaller analogue of the IRP1200: an IRP400 in service in industry. We then report on the design, commissioning and preliminary process-development results from the first of the scaled-up 1.2m capacity CNC polishing machine from Zeeko, Ltd. This machine delivers the 'Classic' bonnet-based process, together with two new processes: fluid-jet polishing and the hybrid soft-grinding/polishing process called 'Zeeko-Grolish.' We indicate how this trio of processes running on the same machine platform with unified software can provide an unprecedented dynamic range in both volumetric removal rate and removal spot-size. This leads into a discussion of how these processes may be brought to bear on optimal control of texture and form. Preliminary performance of the 1.2m machine is illustrated with results on both axially-symmetric and more complex removal regimes. The paper concludes with an overview of the relevance of the technology to efficient production of instrumentation-optics, space optics and segmented telescope mirrors.

The next generation of 30-100 metre diameter extremely large telescopes (ELTs) requires large numbers of hexagonal primary mirror segments. As part of the Basic Technology programme run jointly by UCL and Cranfield University, a reactive atomic plasma technology (RAP(tm)) emerged from the US Lawrence Livermore National Laboratory (LLNL), is employed for the finishing of these surfaces. Results are presented on this novel etching technology. The Inductively Coupled Plasma (ICP) operated at atmospheric pressure using argon, activates the chemical species injected through its centre and promotes the fluorine-based chemical reactions at the surface. Process assessment trials on Ultra Low Expansion (ULE(tm)) plates, previously ground at high material removal rates, have been conducted. The quality of the surfaces produced on these samples using the RAP process are discussed. Substantial volumetric material removal rates of up to 0.446(21) mm ³/s at the highest process speed (1,200 mm/min) were found to be possible without pre-heating the substrate. The influences of power transfer, process speed and gas concentration on the removal rates have been determined. The suitability of the RAP process for revealing and removing sub-surface damage induced by high removal rate grinding is discussed. The results on SiC samples are reported elsewhere in this conference.

Mechanical grinding and shaping of optical materials imparts damage that manifests itself as defects and cracks that can propagate well below the surface of the optic. Mitigation of damage is necessary to preserve the integrity of the optic and relieve residual stress that can be detrimental to its performance. Typically, a sequence of subsequent polishing steps with finer and finer grit sizes is used to remove damage, but the process can be painfully slow especially for hard materials such as silicon carbide and often fails to remove all the damage. Reactive Atom Plasma (RAP^TM) processing, a non-contact, atmospheric pressure plasma-based process, has been shown to reveal and mitigate sub-surface damage in optical materials. Twyman stress tests on thin glass and SiC substrates demonstrate RAP's ability to relieve the stress while at the same time improving surface form.

The second 8.4 m primary mirror and its active support system were delivered to the Large Binocular Telescope in September 2005. The mirror was figured to an accuracy of 15 nm rms surface after subtraction of low-order aberrations that will be controlled by the active support. The mirror was installed into its operational support cell in the lab, and support forces were optimized to produce a figure accurate to 20 nm rms surface with no synthetic correction. The mirror was polished on a new 8.4 m polishing machine that gives the Mirror Lab the capacity to process up to four 8.4 m mirrors simultaneously, with each mirror going through a sequence of stations: casting furnace, generating machine, polishing machine, and integration with its support cell. The new polishing machine has two carriages for polishing tools, allowing use of two 1.2 m stressed laps during loose-abrasive grinding and early polishing, followed by final figuring with a stressed lap and a small tool for local figuring.

NIAOT has made a stressed lap polishing machine and finished a φ910mm, F/2.0 paraboloid. In the process we found shape control strategy is an important technology for stressed lap polishing tool and this kind of content has not been discussed systematically before. So this paper mainly dedicates to the method of lap shape control. Firstly a mathematical model of stressed lap is introduced. Then three shape control methods are put forward one by one concerning aspects as shape accuracy and deformation hysteresis. The fundamental method is least square algorithm. On the base of it we put forward its reformation form: least square algorithm with damping factor. To get more satisfied performance a new algorithm using optimization under constrains of linear inequalities is proposed. Through theoretical analysis and computer simulation some comparisons are made among three methods. Finally we have done experiments using stressed lap polishing machine in NIAOT and the results obtained substantiate the feasibility and efficiency of our method.

The design, manufacture and support of the primary mirror segments for the GMT build on the successful primary mirror systems of the MMT, Magellan and Large Binocular telescopes. The mirror segment and its support system are based on a proven design, and the experience gained in the existing telescopes has led to significant refinements that will provide even better performance in the GMT. The first 8.4 m segment has been cast at the Steward Observatory Mirror Lab, and optical processing is underway. Measurement of the off-axis surface is the greatest challenge in the manufacture of the segments. A set of tests that meets the requirements has been defined and the concepts have been developed in some detail. The most critical parts of the tests have been demonstrated in the measurement of a 1.7 m off-axis prototype. The principal optical test is a full-aperture, high-resolution null test in which a hybrid reflective-diffractive null corrector compensates for the 14 mm aspheric departure of the off-axis segment. The mirror support uses the same synthetic floatation principle as the MMT, Magellan, and LBT mirrors. Refinements for GMT include 3-axis actuators to accommodate the varying orientations of segments in the telescope.

We have nearly completed the manufacture of a 1.7 m off-axis mirror as part of the technology development for the Giant Magellan Telescope. The mirror is an off-axis section of a 5.3 m f/0.73 parent paraboloid, making it roughly a 1:5 model of the outer 8.4 m GMT segment. The 1.7 m mirror will be the primary mirror of the New Solar Telescope at Big Bear Solar Observatory. It has a 2.7 mm peak-to-valley departure from the best-fit sphere, presenting a serious challenge in terms of both polishing and measurement. The mirror was polished with a stressed lap, which bends actively to match the local curvature at each point on the mirror surface, and works for asymmetric mirrors as well as symmetric aspheres. It was measured using a hybrid reflective-diffractive null corrector to compensate for the mirror's asphericity. Both techniques will be applied in scaled-up versions to the GMT segments.

ELTs will need large optical lenses for imaging optics and atmospheric dispersion correctors. The extreme dimensions of lenses considered in designs at present (up to 1.7 m diameter) pose severe challenges for the specification, production and inspection of the glass blanks. Possible maximum sizes, their very long production time, technical and economical conditions and probable restrictions are discussed. The inspection of glass blanks for ELT transmission optics can rely on methods already introduced for optical glass blanks of conventional sizes and for large mirror blanks of the glass-ceramic ZERODUR(r) for most of their properties. However, especially for the refractive index homogeneity a scale-up still has to be achieved. At present largest homogeneity interferometers have apertures about 500 to 600 mm. The development of larger ones is very time consuming, about 2 - 3 years. There is a need for a close agreement on the required capability of the measurement method between the optical designers and the supplier and to start soon with this since the optical lenses may turn out to be more critical in production than the segments for the primary mirrors.

Corning manufactures several optical materials that can be used as reflective and transmissive optics for telescope optical systems. Corning can manufacture these materials in a large range of sizes and configurations. This paper discusses Corning's portfolio of optical materials and their properties, along with Corning's manufacturing capabilities using these materials. Specific examples of optical blanks that Corning has supplied will be discussed.

We present the concept of using a photon sieve as an inexpensive null-corrector. A photon sieve is a diffractive element consisting of a large number of holes precisely positioned according to an underlying Fresnel Zone Plate geometry. Using diffraction theory we can enlarge the holes significantly beyond the width of a Fresnel zone such that more light is transmitted and greater efficiency is achieved. Added to this, modification of the equations used to generate the hole locations can also permit the construction of any desired wavefront instead of a simple infinite-conjugate ratio focusing optic. This makes it an ideal optic for testing larger components in a null-corrector configuration. In this talk we will present theoretical and experimental results from tests of this idea. These include the fabrication of a 0.1m diameter intensity photon sieve null-corrector specifically for testing a parabolic primary.

The fabrication and metrology of astronomical optics are very demanding tasks. In particular, the large sizes needed for astronomical optics and mirrors present significant manufacturing challenges. One of the long-lead aspects (and primary cost drivers) of this process has traditionally been the final polishing and metrology steps. Furthermore, traditional polishing becomes increasingly difficult if the optics are aspheric and/or lightweight. QED Technologies (QED(r)) has developed two novel technologies that have had a significant impact on the production of precision optics. Magnetorheological Finishing (MRF(r)) is a deterministic, production proven, sub-aperture polishing process that can enable significant reductions in cost and lead-time in the production of large optics. MRF routinely achieves surface figure accuracy of better than 30 nm peak-to-valley (better than 5 nm rms) and microroughness better than 1 nm rms on a variety of glasses, glass ceramics and ceramic materials. Unique characteristics of MRF such as a comparatively high, stable removal rate, the conformal nature of the sub-aperture tool and a shear-mode material removal mechanism give it advantages in finishing large and lightweight optics. QED has, for instance, developed the Q22-950F MRF platform which is capable of finishing meter-class optics and the fundamental technology is scalable to even larger apertures. Using MRF for large optics is ideally partnered by a flexible metrology system that provides full aperture metrology of the surface to be finished. A method that provides significant advantages for mirror manufacturing is to characterize the full surface by stitching an array of sub-aperture measurements. Such a technique inherently enables the testing of larger apertures with higher resolution and typically higher accuracy. Furthermore, stitching lends itself to a greater range of optical surfaces that can be measured in a single setup. QED's Subaperture Stitching Interferometer (SSI(r)) complements MRF by extending the effective aperture, accuracy, resolution, and dynamic range of a standard phase-shifting interferometer. This paper will describe these novel approaches to large optics finishing, and present a variety of examples.

The Giant Magellan Telescope (GMT) uses seven 8.4-m diameter segments to create a giant primary mirror, 25 meters across with focal ratio f /0.7. The off-axis segments will be difficult to measure accurately, as they have 14.5 mm departure from the nearest fitting sphere! The test configuration adopted uses a large 3.75-m powered mirror to fold the light path and provide most of the aspheric correction, with a smaller mirror and computer generated hologram (CGH) providing the additional correction. These optics will be aligned to a vibration-insensitive interferometer using a combination of optical references created by the CGH and metrology with a laser tracker. Some key challenges for this system are presented here including, the system alignment, the large fold mirror, and the mechanical structure. Analysis of the optical test shows that it will meet GMT specifications, including the difficult requirement that the separate segments have matching radius of curvature. Additional corroborative testing will be performed to assure that the mirror segments are correctly figured.

We give a progress report on an application of a new class of versatile optical elements pioneered by our laboratory: By coating liquids we create reflective surfaces that can be shaped by rotation into a parabolic mirror. Coated ferrofluids can also be shaped with magnetic fields. Low cost is what makes rotating mercury LM Telescopes interesting. However, they are limited by the fact that they cannot be tilted. We are now working on a new generation of LMs that can be tilted. The goal is to produce large inexpensive LMTs that can be tilted by at least twenty degrees. Early work demonstrated a tilted LM that used a high viscosity liquid. An extrapolation law, confirmed by our experiments, shows that it should be possible to tilt LMs by twenty degrees, assuming a liquid having a few times the viscosity of glycerin. Rotating nanoengineered LMTs are interesting even without tilting, since their lower weight would make then less costly than Hg mirrors and high viscosity makes them less sensitive to winds. We have made two major recent technological breakthroughs: We have made a robotic machine which is capable of producing the large quantities of coating material required for large mirrors. We have also developed a technique that allows us to coat the appropriate class of liquids by simply spraying the nanoengineered coating on them. In this contribution, we present optical tests of our liquids as well as optical shop tests of rotating mirrors.

Under contract from the Cornell-Caltech Atacama Telescope Project (CCAT), Composite Mirror Applications, Inc. (CMA) has undertaken a feasibility design study for the use of Carbon Fiber Reinforced Plastic (CFRP) panels in forming the primary mirror surface. We review some of the past projects using CFRP panel technology for millimeter and submillimeter wavelength radio astronomy telescopes. Pros and cons of the technology are discussed. A particular panel configuration was proposed and computer modeled with finite element analysis (FEA). The technology of replicated CFRP panels for short wavelength radio astronomical telescopes is mature and cost effective. For shorter wavelengths into the IR and visible, it is becoming a very attractive alternative to traditional, heavy glass or metal technologies.

The GREGOR telescope of the Teide Observatory will be upon start of operations the first ground-based telescope with main optics made entirely of a silicon carbide composite material, namely, "carbon-fiber reinforced silicon carbide" or "Cesic(r)," a product of ECM, Germany. This paper describes the configuration and manufacturing of the GREGOR telescope's main optics: the primary (1.5 m), secondary (0.42 m), and tertiary (0.35 m) mirrors.

The 25 m aperture Cornell Caltech Atacama Telescope (CCAT) will be the first segmented telescope of its size and precision. A new technology was required to be able to economically manufacture the segments for the primary mirror. This technology had to be a low cost, low risk, volume manufacturing process in addition to meeting all of the optical and mechanical requirements. The segments had to be lightweight (10-15 kg/m²), have high specific stiffness and be thermally stable. The segments had to have sufficient robustness for practical transport and use and be compatible with high-reflectivity coatings. ITT has designed a replicated, lightweight glass mirror solution to these manufacturing problems. This technology can be used to fabricate segments for CCAT. It can be used to fabricate segments for visible wavelength segmented telescopes or any other application requiring lightweight optics in large quantities. This technology enables the fabrication of large, lightweight mirror segments in a few weeks to a couple of months, depending on the figure requirements. This paper discusses the design of these mirrors and presents demonstrated results to date, including a 0.5 m diameter, 8 kg/m² borosilicate mirror blank and 0.2 m diameter replicated borosilicate mirrors.

Presented are results of continuing optical mirror development program for the NSF ULTRA Telescope. Development of a 16-inch f/4.0 parabolic mirror has been undertaken to adequately define scale-up fabrication procedures for 1m and 1.4m mirrors. 16-inch mirrors have been produced to λ/15 rms ( λ=633nm) in the wavefront. These mirrors have been used to produce astronomical images in a Newtonian telescope and yielded quality optical images. Presented will be results of the fabrication of the 1m, f/3 parabolic primary mirror mandrel for the 1m ULTRA Telescope. Also presented will be lab test data and astronomical mages produced under the 16-inch program as well as test data from the replications from the f/3 1m parabola.

The recently commissioned system for aluminizing the 8.408 meter diameter Large Binocular Telescope mirrors has a variety of unusual features. Among them are aluminizing the mirror in the telescope, the mirror is horizon pointing when aluminized, boron nitride crucibles are used for the sources, only 28 sources are used, the sources are powered with 280 Volts at 20 kHz, high vacuum is produced with a LN2 cooled charcoal cryo-panel, an inflatable edge seal is used to isolate the rough vacuum behind the mirror from the high vacuum space, and a burst disk is mounted in the center hole to protect the mirror from overpressure. We present a description of these features. Results from aluminizing both primary mirrors are presented.

For the planned extremely large telescope projects not only the primary mirror diameters, but also the dimensions of the other optical components are increasing. For the involved manufacturers of astronomical filters technical issues like polishing, coating, measurement, handling and cementing are demanding. Not only the availability of monolithic glass substrates of the required dimensions is critical, but also the required glass quality regarding homogeneity, bubbles, inclusions, and striae. Additionally an individual production of such unique astronomical components is an economical risk, as it does not fit to the usual mass production of small filter components. It is the goal of this paper to call attention to this potential critical path for the future astronomical projects. The status of the filter glass production at SCHOTT and the development needs for these challenging components are discussed.

The Gemini twins were the first large modern telescopes to receive protected Silver coatings on their mirrors in 2004. We report the performance evolution of these 4-layer coatings in terms of reflectivity and emissivity. We evaluate the durability of these thin films by comparison to the evolution of some samples that we have produced and exposed since 2002. Finally, we will explain our maintenance plan.

The Large Synoptic Survey Telescope (LSST) baseline design includes aluminum coating for the large mirrors in its 3 element modified Paul Baker optical design. The 8.4 meter diameter of the primary provides a significant challenge to the LSST coating plans however such coatings have successfully achieved for this size aperture. LSST also recognizes that the use of mirror coatings with higher reflectivity and durability would significantly benefit its science by increasing its overall throughput and improving its operational efficiency. LSST has identified Lawrence Livermore National Laboratory (LLNL) blue-shifted protected silver coating as a possible candidate to provide this blue wavelength performance. A study has been started to assess the performance of these and other coatings in the observatory environment. We present the details of this ongoing program, the results obtained so far, and related coating tests results. LSST has also engaged in collaboration with the Gemini Telescope in the development and testing of an Al-Ag coating based on their current recipe. The first results of these tests are also included in this report.

The Large Synoptic Survey Telescope (LSST) is a unique, three-mirror, modified Paul-Baker design with an 8.4m primary, a 3.4m secondary, and a 5.0m tertiary feeding a camera system that includes corrector optics to produce a 3.5 degree field of view with excellent image quality (<0.3 arcsecond 80% encircled diffracted energy) over the entire field from blue to near infra-red wavelengths. We describe the design of the LSST camera optics, consisting of three refractive lenses with diameters of 1.6m, 1.0m and 0.7m, along with a set of interchangeable, broad-band, interference filters with diameters of 0.75m. We also describe current plans for fabricating, coating, mounting and testing these lenses and filters.

This paper describes the development of a Carbon Fiber-Reinforced Plastics (CFRP) structure for the interferometric instrument LINC-NIRVANA (LN) at the Large Binocular Telescope (LBT) Arizona, USA. This structure carries all components between the two "bent" Gregorian foci of the individual telescopes necessary to combine the light of the two arms coherently. Especially developed for aerospace and defence, CFRP materials now find widespread use across a number of other applications where their special properties are beneficial. We will profit in LN from the good rigidity, high strength, low thermal expansion, low mass and high damping properties of CFRP. An extended Finite Element Analysis was performed to simulate the properties of the structure for different telescope positions and different temperatures. We built a 560 mm x 550 mm x 385 mm test piece of the LN optical bench for flexure tests to confirm the results of the Finite Element Analysis. The complete LN instrument with a mass of 7.5 tons will be mounted at a tilting unit to simulate the different telescope positions.

The focus of the ULTRA Project is to develop and test Ultra-Lightweight Technology for Research applications in Astronomy. The ULTRA project is a collaborative effort involving the private firm Composite Mirror Applications, Inc (CMA) and 3 universities: University of Kansas, San Diego State University, and Dartmouth College. Funding for ULTRA is predominately from a NSF three year MRI program grant to CMA and KU with additional support from CMA, KU and SDSU. The goal of the ULTRA program is to demonstrate that a viable alternative exists to traditional glass mirror and steel telescope technology by designing, fabricating and testing a research telescope constructed from carbon fiber reinforced plastic (CFRP) materials. In particular, a 1m diameter, Cassegrain telescope optics set and optical tube assembly (OTA) are being designed and fabricated by CMA. The completed telescope will be deployed at SDSU's Mt Laguna Observatory in a refurbished structure (new dome and mount provided via KU and SDSU). We expect that a successful completion and testing of this project will lead to future use of CFRP technology in larger telescopes and segmented telescopes. This paper describes the OTA (optical tube assembly) that has been developed for the ULTRA project. The mirror technology is described in another paper in this conference. A poster describes the ULTRA project overview in more detail.

Optimization programs are used routinely in the design of precision structures such as radio telescopes, but design optimization is merely the beginning, rather than the end, of the process. After selecting appropriate member sizes for the optimized solution, careful attention must be paid to the design of the connections to ensure that the effective stiffness of a given member matches that of the optimized design. Given that members rarely span directly to their working points, the effective stiffness of a member is actually a combination of the member cross-section stiffness and the stiffness of the connections at each end. This paper describes the procedure used for the design of a large radio telescope with tubular members and bayonet style connections. Initially, a parametric study was performed to establish gusset plate thicknesses and widths for various tube cross-sections so that the resulting tube/gusset subassembly would match the stiffness of the tubing; the results of this study provided a starting point for designing the connections. Following optimization and member selection for the overall structure, detailed finite element models were constructed for selected connections to assess the effective stiffness of each member framing into these connections. The overall goal was to hold the effective stiffnesses to within a given tolerance. This was accomplished by adjusting plate thicknesses, plate widths, tube-to-plate engagement lengths, and, in a few cases, actually changing the member crosssection to compensate for excessive stiffness or softness at a given connection.

In the design of high precision wheel-on-track systems for large telescopes, the azimuth track presents a significant challenge. Generally, the track must be aligned very accurately to provide good pointing performance and must have high hardness to withstand the contact stresses. It is also advantageous, in terms of both performance and stress, to have a continuous rolling surface with no gaps. Such a surface can be achieved by using a welded track, but it is challenging to maintain alignment and surface hardness during the welding process. For future designs, it is useful to understand what practical limits have been reached during previous installations. The azimuth track for the Large Millimeter-wave Telescope (LMT/GTM) serves as an excellent example of this type of system. It is 39.6m diameter and has been installed, aligned, and welded on site. As of early 2005, it has been supporting the weight of the alidade, and some initial rotations of the structure have taken place. The achieved alignment accuracy and hardness performance are presented, together with lessons learned during the installation, welding, and initial use of the track.

The 1-meter Swedish Solar Telescope (SST) obtains images of the solar surface with an unprecedented resolution of 0.1 arcsec. It consists of a relatively slender tower with on top only the vacuum turret for reflecting downward the solar beam and no protective dome. This is a favourable situation to get good local seeing. Just in the case of some wind, seeing is best for daytime observations, therefore the precision bearings and drives of the elevation- and azimuth axis of the turret have to be stiff against wind. This requires line contact between the meshing teeth of the large gear wheel and the pinion. High preload forces to achieve line contact are not allowed because of appearing stick-slip effects. To reduce the risk on stick-slip a special design of the teeth for high stiffness combined with low friction and smooth transition from one tooth to the next was made. Furthermore, extreme precision in the fabrication was pursued such that relatively small contact forces give already line contact. This required a special order of the successive fabrication steps of the combination of bearing and gear teeth. An additional problem was the relatively thin section of the bearings required for a compact turret construction, needed for best local seeing and minimum wind load. Solutions for all these problems will be discussed. For the large gears the exceptional good DIN quality class 4 for the pitch precision and straightness plus direction of the teeth faces was achieved.

The pointing accuracy of the NASA Deep Space Network antennas is significantly impacted by the unevenness of the antenna azimuth track. The track unevenness causes repeatable antenna rotations, and repeatable pointing errors. The paper presents the improvement of the pointing accuracy of the antennas by implementing the track-level-compensation look-up table. The table consists of three axis rotations of the alidade as a function of the azimuth position. The paper presents the development of the table, based on the measurements of the inclinometer tilts, processing the measurement data, and determination of the three-axis alidade rotations from the tilt data. It also presents the determination of the elevation and cross-elevation errors of the antenna as a function of the alidade rotations. The pointing accuracy of the antenna with and without a table was measured using various radio beam pointing techniques. The pointing error decreased when the table was used, from 7.5 mdeg to 1.2 mdeg in elevation, and from 20.4 mdeg to 2.2 mdeg in cross-elevation.

The W. M. Keck Observatory recently completed an upgrade to the Shutter Drive System on the Keck 1 dome. Due to three major failures on the shutters we decided to undertake a multimillion dollar, multiyear effort to upgrade the drive system. The intention was to increase the system safety factors, to prevent potential problems, to improve maintenance of the system, and to add the capability of the shutter being used as a tracking windscreen, reducing wind effects on the telescope, thereby improving observing. Our solution included the replacement of the drive system with a new drive train and control mechanism, as well as various modifications to existing infrastructure. We'll describe the project from inception to conclusion, and illustrate various approaches helpful to managing this large project while minimizing observatory downtime. We'll discuss control schemes, safety features, failure mode investigations and some heat dissipation concerns. We'll also describe work scheduling, and some prototyping options helpful to ensure success of the project. Finally we'll present some lessons learned from retrofitting a large, essential system of an operating telescope.

Many antennas, such as the 100-m Green Bank Telescope, use a wheel-on-track systems in which the track segments consist of wear plates mounted on base plates. The wear plates are typically 2 to 3 inches thick and are case hardened or through hardened. The base plates are usually 3 to 4 times thicker than the wear plates and are not hardened. The wear plates are typically connected to the base plates using bolts. The base plates are supported on grout and anchored to the underlying concrete foundation. For some antennas, slip has been observed between the wear plate and base plate, and between the base plate and the grout, with the migration in the wheel rolling direction. In addition, there has been wear at the wear plate/base plate interface. This paper is an update on the evaluation of GBT track retrofit. The paper describes the use of three-dimensional non-linear finite element analyses to understand and evaluate the behavior of (1) the existing GBT wheel-on-track system with mitered joints, and (2) the various proposed modifications. The modifications include welding of the base plate joints, staggering of the wear plate joints from the base plate joints, changing thickness of the wear plate, and increasing bolt diameter and length. Parameters included in the evaluation were contact pressure, relative slip, wear at the wear plate/base plate interface, and bolt shears and moments.

This paper describes the studies performed to establish a baseline conceptual design of the Segment Support Assembly (SSA) for the Thirty Meter Telescope (TMT) primary mirror. The SSA uses a combination of mechanical whiffletrees for axial support, a central diaphragm for lateral support, and a whiffletree-based remote-controlled warping harness for surface figure corrections. Axial support whiffletrees are numerically optimized to minimize the resulting gravityinduced deformation. Although a classical central diaphragm solution was eventually adopted, several lateral support concepts are considered. Warping harness systems are analyzed and optimized for their effectiveness at correcting second and third order optical aberrations. Thermal deformations of the optical surface are systematically analyzed using finite element analysis. Worst-case performance of the complete system as a result of gravity loading and temperature variations is analyzed as a function of zenith angle using an integrated finite element model.

The Thirty Meter Telescope (TMT) project is a partnership between ACURA, AURA, Caltech, and the University of California. The design calls for a 3.6 m diameter secondary mirror and an elliptical tertiary mirror measuring more than 4 m along its major axis. Each mirror will weigh more than two metric tons and must be articulated to compensate for deformation of the telescope structure. The support and control of these "smaller optics" pose significant challenges for the designers. We present conceptual designs for active and passive figure control and articulation of these optics.

In the ELTs the weight of the mirror-systems is very important. In fact, the dimensioning both of the support structure and the auxiliary components, such as bearings and drives, depend on it. The mirrors require very stiff structures able to react quickly to dynamic and static stresses. Lightness and stiffness are therefore decisive elements to have a constant and excellent control of the mirror itself. An ultra-light and ultra-stiff panel, directly coupled to the mirror through actuators, allows to reduce to the minimum the quantity of material for the mirror and thus reducing also the weight, always guaranteeing the stiffness requirements. Therefore, this panel becomes an element constituting the mirror itself and it is also charged with the task of connection with the main structure of the cell. A chance for guaranteeing this weight-stiffness ratio is given by the use of the carbon fibre. Particularly, the use of high modulus fibre (pitch fibre) allows to obtain ultra-light mirror support structures with a 60% saving of weight compared to an equivalent steel structure. The in-depth study of the materials used (resin system, Carbon fibre type, adhesives, inserts) and the construction process, the number and the repeatability of the pieces, the experience acquired during the design and construction phases of the ALMA Prototype (Atacama Large Millimeter Array) allow to guarantee a proper control of the quality of the product with accessible and convenient costs considering also that the use of these materials allows to have lighter structures with lower operational costs and the maintenance of the materials in the years requires a lower use of resources.

SIM PlanetQuest (SIM) is a large (9-meter baseline) space-borne optical interferometer that will determine the position and distance of stars to high accuracy. With microarcsecond measurements SIM will probe nearby stars for Earth-sized planets. To achieve this precision, SIM requires very tight manufacturing tolerances and high stability of optical components. To reduce technical risks, the SIM project developed an integrated thermal, mechanical and optical testbed (TOM3) to allow predictions of the system performance at the required high precision. The TOM3 testbed used full-scale brassboard optical components and picometer-class metrology to reach the SIM target performance levels. During the testbed integration and after one of the testbed mirrors, M1, was bonded into its mount, some surface distortion dimples that exceeded the optical specification were discovered. A detailed finite element model was used to analyze different load cases to try to determine the source of the M1 surface deformations. The same model was also used to compare with actual deformations due to varied thermal conditions on the TOM3 testbed. This paper presents the studies carried out to determine the source of the surface distortions on the M1 mirror as well as comparison and model validation during testing. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

The Advanced Technology Solar Telescope (ATST) primary mirror is a 4.24-m diameter, 75-mm thick, off-axis parabola solid meniscus mirror made out of a glass or glass ceramic material. Its baseline support system consists of 120 axial supports mounted at the mirror back surface and 24 lateral supports along the outer edge with an active optics capability. This primary mirror support system was optimized for the telescope at a near horizon position to achieve the best gravity and thermal effects. To fulfill the optical and mechanical performance requirements, extensive finite element analyses using I-DEAS and optical analyses with PCFRINGE have been conducted for the support optimization. Analyses include static deformation (gravity and thermal), frequency calculations, and support system sensitivity evaluations. An influence matrix was established to compensate potential errors using an active optics system. Performances of the primary mirror support system were evaluated from mechanical deformation calculations and the optical analyses before and after active optics corrections. The performance of the mirror cell structure was also discussed.

Hexapods can be an effective means of positioning optics of all sizes, including those within large ground-based telescopes. A hexapod is often a convenient geometry when multiple axes of positioning are required. The paper reviews several small and mid-sized hexapods built for different applications, and emphasizes experience with a three-meter- diameter unit built to position a large optical component. The discussion highlights design tradeoffs in precision, including repeatability, resolution and accuracy, range in multiple axes, and bandwidth of operation, and addresses test and verification of performance. The paper concludes with a discussion and presentation of hexapod concepts for secondary mirror positioning for Thirty Meter Telescope and Cornell Caltech Atacama Telescope.

The reflecting Schmidt plate of the Large sky Area Multi-Object Spectroscopic Telescope (LAMOST) is composed of 24 hexagonal segments, each of which is 1100 mm from corner to corner and 25 mm in thickness. Both segmented mirror active optics and deformable mirror active optics are involved in the Schmidt plate so as to compensate for optical aberration and structural deformation. A prototype of the segment support system with dummy aluminum mirror had been setup and tested during 2003 to 2004, afterwards, based on the evaluation of test, the whole support system was updated to a backlash-free and light-weighted design. For the segmented mirror active optics, the segment mirror support system is to fulfill motions of tip, tilt and piston with three linear positioning actuators. Instead of self-alignment bearing adopted in the early prototype, a centering diaphragm is employed to realize a backlash-free pintle. And a lever with reduction of 10:1 is introduced to each of the three positioning actuator mechanisms, respectively, to obtain greater load capacity and further finer output displacement, as hence releases requirement and cost of the actuators. For better performance, high strength steel blades are used in tension state for pivots of the levers preloaded with longitudinal springs. To gap the mirror segments with respect to each other for making proper space for edge sensors, three adjustable fixtures are implemented for each segment mirror module to do translation and pistion on three conrresponding nodes on the top layer of the gross mirror cell truss before being anchored once and forever. In addition, safety measurements as well as anti-rotation mechanism have been taken into consideration throughout the design and development process. This paper describes the mechanical design and related analysis of the segment mirror support system in detail.

The Academia Sinica, Institute for Astronomy and Astrophysics (ASIAA) is installing the AMiBA interferometric array telescope at the Mauna Loa Observatory, Hawaii. The 6-meter carbon fiber fully steerable platform is mounted on the Hexapod Mount. After integration and equipment with dummy weights, the platform has been measured by photogrammetry to verify its behavior predicted by Finite Element Analysis. The Hexapod servo control is now operational and equipment of the platform with the initial 7 60-cm dishes, the correlator and electronics is underway. Pointing has started with the aid of the optical telescope. We present the status of the telescope after the servo and initial pointing tests have been carried out. We also present the results of platform measurements by photogrammetry.

This paper describes four different drive systems adopted in LAMOST focal plane mechanism to achieve four movements: field derotation, focal plane attitude adjustment, focusing and move aside out of light path for optical checking. Different type drive systems, such as worm gear drive, spur gear drive, friction drive and direct drive, which were devised and used in telescopes in the past years, have their own inherent characteristics and their working conditions. According to feasibility, reliability, suitability and cost effective, friction drive, worm gear drive, ball screw drive and chain drive are selected to as the drive systems for the above four movements. The on-shop test results show that all the drive systems have met the design goals with the accuracy of image field derotation 0.45 arcsec, attitude adjustment 0.24 arcsec, focusing 2 microns and move aside 0.02mm.

This paper describes a high-force PZT-ceramic based linear actuator for long-travel, high resolution applications. Different modes of operation offer high bandwidth dither, step and constant velocity slew motion. The drive is self-locking and does not expend energy to hold a position. This development was originally undertaken for applications in the semiconductor industry and mature serial production actuators are now embedded in machinery to actively collimate heavy optic assemblies weighing 10's of kg in multiple axes with nanometer resolution.

This paper discusses the current status of self supporting precision membrane optical shell technology (MOST) apertures based on thin (25 to 125 um thick) polyimide and polyester films primary shell. Optically relevant doubly curved reflective apertures are realized by inducing permanent curvature into thin substrates that can then be coated. The initial thin nature provides both very low areal density (20 to 200 grams/m²) and compatibility with compact roll stowage. The induced curvature/depth provides the ability to support the shell around the periphery at discrete locations and considerable structural and dynamic stiffness. The discrete mounts also provide an excellent location with which to improve the surface figure and to reject environmental and host structure induced errors. Material microroughness on the leading substrate/coating combination has been measured to down to 3 nm rms over small (100x100um's) sample sizes with white light interferometry. A variety of reflective coated substrates have also been shown to have sub micron rms surface roughness over up to 100mm diameter test apertures using interferometric measurements. Best materials currently have 20nm rms surface roughness noise floors at these sizes. The ability to fabricate shells over a range of prescriptions (R/0.9 to R/2.2) and a range of sizes (0.1 to 0.75m diameter) has been demonstrated. Global surface figure accuracies of 2 to 4 microns rms have been demonstrated at the 0.2m size, and further improvements are anticipated through ongoing improved fabrication techniques (preliminary results indicate sub-micron rms values). The ability of discrete boundary control to improve the shape and maintain it in the face of disturbances (gravity for example) is demonstrated as is the ability to implement high amplitude (multi-wave) Zernike mode surface figure control. Results extending boundary control to interferometric optical level are also presented.

This paper presents an overview of a step scanning mechanism employing a flexure stage coupled with a dynamically aligned mirror used in the SpIOMM (Spectrometre Imageur de l'Observatoire du Mont Megantic) instrument, an Imaging Fourier Transform Spectrometer (IFTS) concept for ground based telescopes produced in collaboration with ABB and Universite Laval. This instrument can acquire spectra of variable resolutions up to R = λ/Δλ = 10 000 from the near UV to the near IR (350 nm to 900 nm). It is designed to fit the f/8 focus of the Mont Megantic (Quebec, Canada) 1.6m optical telescope. The innovative aspect of this instrument compared to other imaging spectrometers is the spatial coverage. The FOV covers spans of 12 arc minutes in diameter with a pixel sampling of 0.55 arc seconds. Hence spectra of more than a million scene elements are acquired at each measurement.

High-resolution telescopes require a mechanical stability of fractions of an arc second. Placing such a telescope on top of a tower will improve the local seeing. An open transparent tower of framework minimizes the upward, temperature disturbed air flow. The tower platform has to be extremely stable against rotational motions, which have to be less than fractions of an arc second, unusual in mechanical engineering. Active systems can improve the stability. However, they need sensors for position measurements, active actuators and a control loop. The performance is limited by the available signal-to-noise ratio. Consequently, improvement of the passive stability of large tower structures will significantly contribute to the final stability. Special geometries in steel framework can reach extreme passive stability of a tower platform, particularly against rotational motions. There are several groups of basic geometries, which lead to solutions and we will give a systematic description. The proposed towers can be welded or screwed together from smaller parts. This makes a construction in adverse environments like the Antarctic region within good reach.

An Integral Field Spectrograph basically consists of an Integral Field Unit (IFU) which slices and re-arranges the initial field along the entrance slit of the spectrograph itself. The IFU is usually composed of a slicer mirror array located at the image plane of the telescope and associated with a row of pupil mirrors and a row of slit mirrors. These optical elements are complex surfaces made of many tilted and decentered mirror sub-surfaces. Such elements can be manufactured using glass standard polishing technics instead of monolithic aluminum diamond turning technics. Standard glass polished optics are usually considered more expensive and time consuming than aluminum diamond turned optics. However standard glass manufacturing technics allow reaching high-level performances: accurate roughness (high throughput), sharp edges (about 1 μm), surface form (image quality), etc. In this paper, we propose a new method of manufacturing and an associated design of IFU which significantly reduce both manufacturing costs and time.

Next generation MOS for space as well as ground-based instruments, including NIRSpec for JWST, require a programmable multi-slit mask. A promising solution is the use of MOEMS-based devices such as micromirror arrays (MMA) or micro-shutter arrays (MSA). Both configurations allow remote control of the multi-slit configuration in real time. Engaged in the design studies for NIRSpec, we have developed different tools for the modelling and the characterization of these devices. Since, we have continued our studies with commercial TI MMA and we show that in a 20° ON-OFF configuration, the 3000 contrast requirement is fulfilled for any F# of 8m-class telescopes as well as future ELT's. Within the framework of the JRA on Smart Focal Planes, micro-mirrors have been selected in order to get a first demonstrator of a European MOEMS-based slit mask. We have fixed several key parameters: one micromirror per astronomical object, high optical contrast of at least 3000, tilting angle of 20°, fill factor of more than 90%, size of a micro-element around 100 × 200 μm², driving voltage below 100V. The MMA would also work in a wide range of temperature down to cryogenic temperatures. Based on these parameters, we have designed a new MMA architecture, using a combination of bulk and surface micromachining. A first small test array of micro-mirrors was successfully fabricated and shows the desired mechanical tilting angle of 20° at a driving voltage of about 100V. Preliminary measurements show a surface quality better than lambda/20. Assembly of small test arrays with their electrode chips and design of larger arrays are under way.

A slicer mirror is a complex surface composed by many tilted and decentered mirrors sub-surfaces. The major difficulty to model such a complex surface is the large number of parameters used to define it. The Zemax's multi-configuration mode is usually used to specify each parameters (tilts, curvatures, decenters) for each mirror sub-surface which are then considered independently. Otherwise making use of the User-Defined Surface (UDSDLL) Zemax capability, we are able to consider the set of sub-surfaces as an unique surface. Such a UDS-DLL tools facilitate Integral Field Unit (IFU) designs and make optimization faster by a factor 2-5 compared with the classical multi-configuration mode. Furthermore, analysis and tolerancing can be performed with equal results although some analyses are facilitated in particular those that need to consider several slices such as the cross-talk due to diffraction. In this paper, we present a set of such a UDS-DLL tool to model all types of slicer mirror arrays used in current IFU designs.

We are currently developing a conceptual design for a future ELT NIR large field of view imager-spectrograph, SMART-MOS, along with several science cases from which top level instrument requirements are being established. This project form part of the EU Framework 6 Joint Research Activity on Smart Focal Planes. The instrument will offer multiobject spectroscopy, which will include the long slit mode, and image over a field of view of 1 to 2 arcmin, with high multiplexing capability. The use of a simple AO ground layer correction is envisaged but the instrument will not work at the diffraction limit though. Multi slits are the base line for the field selector, even when multi-IFU type instrument might be considered at later stage. There are two possible operational concepts for SMART-MOS, each of which involving different technologies: MOEMS type devices or sliding bars. We describe in this contribution the science cases and discuss the most relevant requirements which will drive the development. Preliminary optical and mechanical concepts are also sketched which include details about the most relevant part of the instrument.

We describe our work towards the manufacture of micro-optical arrays using freeform diamond machining techniques. Simulations have been done to show the feasibility of manufacturing micro-lens arrays using the slow-tool servo method. Using this technique, master shapes can be produced for replication of micro-lens arrays of either epoxy-on-glass or monolthic glass types. A machine tool path programme has been developed on the machine software platform DIFFSYS, allowing the production of spherical, aspherical and toric arrays. In addition, in theory spatially varying lenslets, sparse arrays and dithered lenslet arrays (for high contrast applications) are possible to produce. In practice, due to the diamond tool limitations not all formats are feasible. Investigations into solving this problem have been carried out and a solution is presented here.

As part of the Starbug development, a range of actuator technologies have been prototyped and trialled in the quest to develop this novel focal plane positioning system. The Starbug concept is a robotic positioning system that deploys multiple payloads, such as pickoff optics, optical fibres and other possible devices to micron level accuracy over a flat or curved focal plane. The development is aimed at addressing some of the limitations of other positioning systems to provide a reliable, cost effective way of positioning multiple payloads in ambient and cryogenic environments. In this paper we identify the specification and required characteristics of the micro-robotic actuators as applied to the MOMSI instrument concept, present descriptions of some of the prototypes along with the results from characterisation and performance tests. These tests were undertaken at various orientations and temperatures as well as using different actuator concepts.

We explore the range of wide field multi-object instrument concepts taking advantage of the unique capabilities of the Starbug focal plane positioning concept. Advances to familiar instrument concepts, such as fiber positioners and deployable fiber-fed IFUs, are discussed along with image relays and deployable active sensors. We conceive deployable payloads as components of systems more traditionally regarded as part of telescope systems rather than instruments - such as adaptive optics and ADCs. Also presented are some of the opportunities offered by the truly unique capabilities of Starbug, such as microtracking to apply intra-field distortion correction during the course of an observation.

A particular flavor of multi-object spectrographs uses pick-off and steering mirrors. These mirrors perform target selection by relaying the optical beams from variable positions in the focal plane to fixed optics in the instrument. Examples of instrument conceptual designs based on this system are presented and illustrated. Particular emphasis is given to the beam steering mirror (BSM) environment which requires the following mechanical motions: translation, rotations and possibly active deformation of the optical surface. A BSM design featuring translation, tip-tilt and a toroidal deformable surface is presented. First results from a prototype development are also presented. A metrology system including wavefront sensing allows to measure and control the position of the optical beam. This system, required for system tests, integration, calibration and operation, is presented. This work is part of the Laboratoire d'Astrophysique de Marseille (LAM) contribution to the beam manipulation work package of the OPTICON smart focal plane.

Recent advances in the design of all reflective integral field units have led engineers to look for new techniques to manufacture monolithic mirror arrays for use in such instruments. One such design is being developed at the UKATC for use on the Mid-Infrared Instrument (MIRI) on the James Webb Space telescope. The MIRI instrument will contain four integral field units with image slicer and re-imaging mirror arrays manufactured at Cranfield University. The mirror arrays have been designed with particular attention to the requirements of precision machining and subsequent metrology. The philosophy of "design for manufacture" has led to the production of mirror arrays with unrivalled levels of accuracy. Initially, this paper will describe the opto-mechanical design of the mirror arrays. The paper will then discuss the diamond turning manufacturing technique specially developed to machine these complex components. The paper will also describe the precision metrology capability developed specifically for the MIRI project that is used to accurately measure mirror locations and surface form errors. Finally, the paper will present the results obtained so far for the mirror arrays being prepared for the IFU verification model and prototype.

The most difficult aspects in manufacturing a reflective slit substrate are achieving a precisely fabricated slit surrounded by an optically flat surface. A commonly used technique is to polish a metal substrate that has a slit cut by electric discharge machine (EDM) methods. This process can produce 'optically flat' surfaces; however, the EDM can produce a slit with edge roughness on the order of 10 microns and a RMS field roughness of ~1 micron. Here, we present a departure from these traditional methods and employ the advantages inherent in integrated circuit fabrication. By starting with a silicon wafer, we begin with a nearly atomically flat surface. In addition, the fabrication tools and methodologies employed are traditionally used for high precision applications: this allows for the placement and definition of the slit with high accuracy. If greater accuracy in slit definition is required, additional tools, such as a focused ion beam, are used to define the slit edge down to tens of nanometers. The deposition of gold, after that of a suitable bonding layer, in an ultra-high vacuum chamber creates a final surface without the need of polishing. Typical results yield a surface RMS-roughness of approximately 2nm. Most of the techniques and tools required for this process are commonly available at research universities and the cost to manufacture said mirrors is a small fraction of the purchase price of the traditional ones.

A new technique for creating optical masks with a transmittance that varies spatially according to an arbitrary usersupplied equation is discussed. Initial fabrication and testing demonstrates the viability of the technique, as well as showing the effect of various deposition parameters in the resulting product. The test data are compared to both simulated and ideal results. The application of this technique to the creation of a coronagraphic filter with strong central attenuation and minimal edge diffraction is also discussed.

Optical systems made for space-based interferometric missions like LISA or SIM must be made of materials that can endure significant accelerations and temperature fluctuations while staying dimensionally stable. Temperature-induced effects can be reduced with thermal shielding techniques and estimated using the thermal expansion coefficient. However, the stability is often limited by virtually unquantified material internal relaxation processes. In this paper we describe the experimental layout and present the status of our experiments to measure the dimensional stability of Zerodur and Hexoloy SA^® silicon carbide using hydroxide-bonding and discuss its feasibility for the LISA mission.

The JWST Integrated Science Instrument Module (ISIM) includes a large metering structure (approx. 2m × 2m × 1.5m) that houses the science instruments and guider. Stringent dimensional stability and repeatability requirements combined with mass limitations led to the selection of a composite bonded frame design comprised of biased laminate tubes. Even with the superb material specific stiffness, achieving the required frequency for the given mass allocations in conjunction with severe spatial limitations imposed by the instrument complement has proven challenging. In response to the challenge, the ISIM structure team considered literally over 100 primary structure topology and kinematic mount configurations, and settled on a concept comprised of over 70 m of tubes, over 50 bonded joint assemblies, and a "split bi-pod" kinematic mount configuration. In this paper, we review the evolution of the ISIM primary structure topology and kinematic mount configuration to the current baseline concept.

The Near-Infrared Spectrograph (NIRSpec) onboard the James Webb Space Telescope can be reconfigured in space for astronomical observation in a range of filter bands as well as spectral resolutions. This will be achieved using a Filter wheel (FWA) which carries 7 transmission filters and a Grating wheel (GWA) which carries six gratings and one prism. The large temperature shift between warm launch and cryogenic operation (30K) and high launch vibration loads on the one hand side and accurate positioning capability and minimum deformation of optical components on the other hand side must be consolidated into a single mechanical design which will be achieved using space-proven concepts derived from the successful ISO filter wheel mechanisms which were manufactured and tested by Carl Zeiss. Carl Zeiss Optronics has been selected by Astrium GmbH for the implementation of both NIRSpec wheel mechanisms. Austrian Aerospace and Max-Planck-Institut fur Astronomie Heidelberg (MPIA) will contribute major work shares to the project. The project was started in October 2005 and the preliminary designs have been finalized recently. Critical performance parameters are properly allocated to respective hardware components, procurements of long-lead items have been initiated and breadboard tests have started. This paper presents an overview of the mechanism designs, discusses its properties and the approach for component level tests.

Following a warm launch in 2013 the MIRI instrument aboard JWST will be operated for a lifetime of 5-10 years in the L2-orbit at a temperature of ~6 K. The main requirements for its three wheel mechanisms include: (1) reliability, (2) optical precision, (3) low power dissipation, (4) high vibration capability, (5) functionality at 4 < T < 300 K. The filter wheel carries broad and narrow band spectral filters, coronographic masks and a prism on its 18 positions. Each of the two spectrometer wheels is equipped with two disks on both sides of a central torque motor, one of them carries 6 gratings, the other a dichroic/mirror arrangement. The optical positions are defined by a ratchet mechanism. No closed loop control is required; therefore the long time average heat dissipation is negligible. A new ratchet mechanism had to be developed to satisfy a 120° increment of only three positions for the spectrometer wheels. Extensive cold and warm tests were performed on the development models of the filter and spectrometer wheels at MPIA. These results stimulated numerous improvements in the mechanical and thermal design which are now to be implemented in the qualification and flight models developed jointly with Carl Zeiss. Synergies are expected from a similar development of the NIRSPEC wheels, in which MPIA and Carl Zeiss are involved.

HERSCHEL's 3.5 m primary mirror will be passively cooled to T ~ 80 K in the L2 orbit. In order to reduce the effects of the remaining high thermal background on the sensitive far infrared detectors (60..210 μm), a focal plane chopper is a vital element in the entrance optics of the imaging and spectroscopic instrument PACS. A gold coated 32 × 26 mm² plane mirror, suspended by two flexural pivots and driven by a linear motor, allows for precise square wave chopping with up to 9° throw at a frequency 10 Hz with a position accuracy of 1 arcmin. The power required at T ~ 4 K is about 1 mW. The chopper has undergone an extensive qualification programme, including 650 million cold chop throws, 15 cold-warm-cold thermal cycles, 3-axis 26 G-vibration at T ~ 4 K etc. Five models were built and thoroughly tested; the flight model of the chopper is now integrated into the flight model of PACS, ready for the HERSCHEL/PLANCK launch in 2008 by an ARIANE5 rocket and the following 5-year mission.

The increasing difficulty of metrology requirements on projects involving optics and the alignment of instrumentation on spacecraft has reached a turning point. Requirements as low as 0.1 arcseconds for the static, rotational alignment of components within a coordinate system cannot be met with a theodolite, the alignment tool currently in use. The ¹"theoferometer" is an interferometer mounted on a rotation stage with degrees of freedom in azimuth and elevation for metrology and alignment applications. The success of a prototype theoferometer in approaching these metrology requirements led to a redesign stressing mechanical, optical, and software changes to increase the sensitivity and portability of the unit. This paper covers the characteristic testing of the first prototype, improvements made to design a second prototype, and planned demonstration of the redesigned theoferometer's capabilities as a "theodolite replacement" and low-uncertainty metrology tool.

During the IFU prototype study that the laboratory led for ESA in the frame of the JWST/NIRSpec technological development studies in 2004, an optomechanical concept was realized and tested at the laboratory. As some limitations of this design were demonstrated, the laboratory decided to develop a new concept of optomechanical interface to support glass image slicers, compliant with space environment specifications. This development was conducted in a very short time and with a tiger team. This prototype was designed and realized at LAM. It consists in an invar monolithic mechanical mount (including three blades) supporting an assembly of three zerodur optical parts tight together thanks to optical contact. The interface between invar and zerodur is done with glue. This prototype has been qualified at 10.5 g rms and 77K. It demonstrates the stability of the optical part within +/- 9 arcsec. The test campaign points up the evolution of the glue properties during time and thermal cycles. Thanks to a detailed FEM analysis, the change of the glue material damping has been estimated.

This paper deals with the optical design and preliminary optomechanical tolerances of HRIC, the High Resolution Imaging Channel of the SIMBIO-SYS instrument, selected as part of the scientific payload for the ESA cornerstone BepiColombo mission to Mercury. Under the lead of Italy (Principal Investigator: E. Flamini), the project is based on an international co-operation with Institutes from France and Switzerland. Starting from the stringent scientific requirement of 5m ground pixel scale at 400 km from the planet surface, a robust optical design based on a catadioptric Ritchey-Chretien configuration modified with a dedicated corrector camera has been achieved. The optimized configuration is convenient in terms of image quality, number of optical elements, and total length. The channel guarantees a corrected FoV of about 1.5° and allows the achievement of the required resolution with a detector of 2k × 2k pixels. The telescope is diffraction limited, thanks to its focal ratio (F/8), and shows an optimised radiometric flux within the operative spectral range (400 - 900 nm). The channel is equipped with one panchromatic and 3 selective filters. The operation plan foresees the coverage of at least 20% of the whole Hermean surface with the HRIC. The preliminary optomechanical tolerances and the corresponding image quality have been analyzed. Further thermo-mechanical analysis is in progress, which is being analyzed by means of ray-tracing tools for image quality evaluation.

We demonstrate a method for producing a large, inexpensive, highly curved deformable mirror by stretching a thin polymer membrane coated with a reflective, magnetic material over a rigid frame. The membrane tension, thickness profile, and the transmembrane pressure differential determine the curvature of the mirror, while a computer-controlled electromagnet array deforms the membrane, both to correct the figure and to compensate for an aberrated wavefront. A telescope with an eight-inch f5 magnetic-membrane primary mirror and an adaptive-optics wavefront-measurement-andcontrol system was built and tested. The versatility, high surface quality, large actuator stroke, and low cost-to-aperture ratio of this design suggest that magnetic-membrane mirrors can be used to overcome many of the limitations of both deformable and static mirrors made from solid materials.

Glass and metallic image slicer breadboards have been designed, manufactured and tested for MUSE (Multi Unit Spectroscopic Explorer) instrument, a second generation integral field spectrograph developed for the European Southern Observatory (ESO) for the VLT. MUSE is operating in the visible and near IR wavelength range (0.465-0.93 μm) and is composed of 24 identical integral field units; each one incorporates an advanced image slicer associated with a classical spectrograph. This presentation describes the optical design, the manufacturing, component test results (shape, roughness, Bidirectional Reflection Distribution Function - BRDF) and overall system performance (image quality, alignment) of two image slicer breadboards. The first one is made of Zerodur and uses individual optical components polished by a classical method and assembled together by molecular adhesion. This breadboard is a combination of mirrors and mini-lens arrays. The second one is made of metal (copper or invar) using monolithic or segmented optical elements and state-ofthe- art diamond-turning machines. It is composed of two sets of reflective mirrors. We will then conclude with a comparison between these two different breadboards by choosing the most suitable solution for the 24 MUSE image slicers.

We report progress on development of large format silicon immersion gratings (SIG) at UF. Currently SIGs on 4 inch diameter thick silicon disks can be routinely produced with groove periods from 7 microns to 250 microns and blaze angles from 20 degrees to 76 degrees. A new capability of making SIGs from 6 inch diameter silicon disks has also been demonstrated. A new Space Astronomy Instrumentation Lab (SAIL) facility is being established at UF to have a capability of fabricating SIGs on 8 inch diameter silicon disks with up to 4 inch thickness. Our prototype SIG with an 85x50 mm² etched grating area and a 54.7 deg blaze angle has produced a nearly diffraction-limited wavefront, less than 1% integrated scattered light and ghost intensity, a 74% peak blaze efficiency and a R = 55,000 resolving power at 1.55 μm.

The Gemini South Adaptive Optics Imager (GSAOI) to be used with the Multi-Conjugate Adaptive Optics (MCAO) system at Gemini South is currently in the final stages of assembly and testing. GSAOI uses a suite of 26 different filters, made from both BK7 and Fused Silica substrates. These filters, located in a non-collimated beam, work as active optical elements. The optical design was undertaken to ensure that both the filter substrates both focused longitudinally at the same point. During the testing of the instrument it was found that longitudinal focus was filter dependant. The methods used to investigate this are outlined in the paper. These investigations identified several possible causes for the focal shift including substrate material properties in cryogenic conditions and small amounts of residual filter power.

We have successfully fabricated germanium immersion gratings with resolving power of 45,000 at 10 μm by using a nano precision 3D grinding machine and ELID (ELectrolytic In-process Dressing) method. However the method spends large amount of machine times. We propose grooves shape with a new principle for a solid grating, which achieves high performance and lower cost. We have developed volume phase holographic (VPH) grisms with zinc selenide (ZnSe) prisms for spectrograph of the Subaru Telescope and the other telescopes. While a VPH grism with high index prisms achieves higher dispersion, diffraction efficiency of VPH grating decreases toward higher orders. A "quasi-Bragg grating" which inherits advantage of a VPH grating achieves high diffraction efficiency toward higher orders. Wavelength tuners with a pair of counter-rotation prisms for a VPH and quasi-Bragg grating obtain high diffraction efficiency over wide wavelength range. The novel immersion grating, VPH grism with high index prisms, quasi-Bragg grating and wavelength tuners dramatically reduce volumes of astronomical spectrographs.

This paper describes the opto-mechanical design of a large instrument for sub-mm, SCUBA-2, to be commissioned at JCMT. The scientific requirements, specially the large fov and the constraints of the telescope mechanical structure, lead to a complex optical design using freeform aluminium mirrors . The mechanical design is also challenging with large modules to be mounted and aligned in the telescope as well as the cryogenic instrument containing the mirrors, the filters, the dichroics and the detector modules. The cryogenic isostatic mounting, the structural and thermal designs are presented. This includes details of the fabrication of the structure and design of a shutter mechanism for operation at 4K. The results of the first AIV cool-down are also presented.

This paper describes the design and development of an accurate temperature compliant lens mounting technique being used on the camera of the UK-FMOS near infrared spectrograph for operation at the Subaru Telescope in Hawaii. A series of fused silica lenses of up to 4.4kg, 255mm in diameter and operating at temperatures as low as 70K are supported within flexures cut away from stainless steel outer rings. Intermediate low thermal expansion pads are attached to these flexures and in turn bonded to the glass during the alignment process. This mounting method lends itself to the domino chips type of assembly process which can be carried out on a rotary table to maintain accurate axial alignment. A detailed description of the overall design progression including the methods of manufacture, alignment process, adhesive selection, assembly methods and testing is included.

Silicon and germanium are perhaps the two most well-understood semiconductor materials in the context of solid state device technologies and more recently micromachining and nanotechnology. Meanwhile, these two materials are also important in the field of infrared lens design. Optical instruments designed for the wavelength range where these two materials are transmissive achieve best performance when cooled to cryogenic temperatures to enhance signal from the scene over instrument background radiation. In order to enable high quality lens designs using silicon and germanium at cryogenic temperatures, we have measured the absolute refractive index of multiple prisms of these two materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For silicon, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 20 to 300 K at wavelengths from 1.1 to 5.6 μm, while for germanium, we cover temperatures ranging from 20 to 300 K and wavelengths from 1.9 to 5.5 μm. We compare our measurements with others in the literature and provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. Citing the wide variety of values for the refractive indices of these two materials found in the literature, we reiterate the importance of measuring the refractive index of a sample from the same batch of raw material from which final optical components are cut when absolute accuracy greater than ±5 x 10^-3 is desired.

Using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, we have measured the absolute refractive index of five specimens taken from a very large boule of Corning 7980 fused silica from temperatures ranging from 30 to 310 K at wavelengths from 0.4 to 2.6 microns with an absolute uncertainty of ±1 ×10^-5. Statistical variations in derived values of the thermo-optic coefficient (dn/dT) are at the ±2 × 10^-8/K level. Graphical and tabulated data for absolute refractive index, dispersion, and thermo-optic coefficient are presented for selected wavelengths and temperatures along with estimates of uncertainty in index. Coefficients for temperature-dependent Sellmeier fits of measured refractive index are also presented to allow accurate interpolation of index to other wavelengths and temperatures. We compare our results to those from an independent investigation (which used an interferometric technique for measuring index changes as a function of temperature) whose samples were prepared from the same slugs of material from which our prisms were prepared in support of the Kepler mission. We also compare our results with sparse cryogenic index data from measurements of this material from the literature.

We present the SWIFT image slicer and its novel de-magnifying design. It is based on the MPE-3D and SPIFFI image slicers, uses plane mirrors to slice the input field, but achieves a considerable de-magnification through the use of a mosaic of spherical lenses. As only plane and spherical surfaces are used in the design, classical polishing techniques can be applied to achieve very high surface accuracy and quality. This reduces aberrations and scattered light, mandatory for an image slicer working at optical wavelengths and behind an adaptive optics system. Except for the lens mosaic, the SWIFT slicer is built entirely from Zerodur and is assembled using optical contacting. We present a detailed description of the design as well as results of the early stages of its fabrication.

The material property of CLEARCERAM^®-Z series, which is the low thermal expansion glass-ceramics products by Ohara Inc., with an integrated product size of Dia.1.4meter was investigated along with confirmation of the surface finish performances. The material property investigation for the Dia.1.4meter CLEARCERAM^®-Z HS indicated the mean CTE of 0.01×10^-7/degree C, the CTE uniformity (CTEmax.-CTEmin.) of 0.10×10^-7/degree C based on developed precision CTE measurement system with 2ppb/degree C repeatability and the maximum stress birefringence of 4.4nm/cm within the disk, which are meeting the mirror substrate material specification for near future large telescope project (Thirty Meter Telescope project). From the experiments to determine surface finish performance, no practical change was observed for the surface profile in millimeter scan filed per Ion Beam Figuring processing. Also the surface robustness against acid solutions, which are used at mirror cleaning, was proved from dipping tests using Hydrochloric acid and Nitric acid. With the material property based on the precision metrology and the surface finish performances, the suitability of CLEARCERAM^®-Z for telescope mirror substrate application was presented.

Providing toric mirrors with Active Optics techniques will allow generating aspheric surfaces which optical quality avoid high spatial frequencies errors. In order to demonstrate the feasibility of this technique, a link has been established between analytical calculations, finite element modelling and experimental validation. A particular configuration of a flat mono-mode deformable mirror (MDM), called "degenerated configuration", has been analytically calculated, showing how to generate a third order astigmatism aberration (Astm 3) by active deformation. This mirror has been manufactured and tested. A finite element model has been produced in order to correlate simulations with experiments. The deformed optical surface is projected on a Zernike polynomial base, indicating that Astm 3 mode is, within a very high precision, the only aberration generated on the optical surface. Another spherical concave MDM has been modelled as a VLT-SPHERE toric mirror of diameter 133mm, to demonstrate the feasibility of toric surfaces from active optics deformation of a spherical shell. Projection on Zernike base shows that the simulated deformed surface is a combination of a sphere and a quasi pure Astm 3 mode, corresponding to a toroidal surface. Other terms generated, like Astm 5, could benefit of a fine adjustment from the geometry of the substrate.

Corning Incorporated has had success with many of the large optics for different programs. Corning's ability to fuse ULE^® monolithic blanks from smaller portions allows for a wide variety of shapes and configurations. Corning's latest success has come with the Discovery Channel Telescope (DCT) 4.3 meter ULE^® blank, produced for Lowell Observatory. This paper will document the process for the fabrication of the blank from inception to completion and shipment of the blank to the customer. There will be discussion of the manufacturing processes, ULE^® selection, and handling.

Introduction to design thought of a large vacuum sputtering coating plant for astronomical telescope. The coating plant is square and all working cells are installed on a holder inside the chamber. When the plant door open, the holder with working cells is hauled out of chamber, then maintaining, repair and installing mirrors are very easy. Metal film and dielectric film are made with DC and RF magnetron sputtering respectively. The largest diameter of mirror is 1600 mm and the diameter of sputtering target is 160 mm. The whole mirror is coated by the polar coordinate scanning through computer control. There are three advantage: large mirror is sputtered with small power supply, so the cost is saved; By computer controlling working parameter of scanning, better uniformity can achieve; scanning sputtering can correct the mirror surface.

This paper shows the optical transmission evaluated for the two manufactured optical correctors of VST telescope. It reports the external transmission curves and corresponding data values for the two correctors camera which have been designed from Technology Working Group at INAF Astronomical Observatory of Capodimonte in Napoli in collaboration with ESO and realized by Zeiss as part of the whole telescope optical design. The transmission for two-lens corrector and ADC and one-lens corrector, has been analyzed in the wavelength ranges of measured Zeiss AR coating curves. The specifications for antireflection coating of optical components of VST correctors have been given on a wide range (320 ÷ 1014 nm). The transmission curves have been computed at different fields of view positions from the center, in order to analyze if there were significant differences with components glass thickness variation. The transmission values reported will be of reference for the phases of test of the correctors mounted at telescope at Paranal and for the correlated tests and commissioning of the telescope with focal plane camera OMEGACAM.

The next generation of ground-based extremely large telescopes of 30 m to 100 m aperture calls for the manufacture of several hundred sub-aperture segments of 1 m to 2 m diameter. Each annulus of the overall aperture is formed from separate elements of the appropriate off-axis conic section (usually a paraboloid). Manufacture of these segments requires a systematic approach to in- and post-process metrology for all stages of manufacture, including the grinding stage, despite the fact that the resulting ground surface is generally not amenable to optically reflective measurement techniques. To address the need for measurements on such 1 m to 2 m telescope segments, a swing arm profilometer has been constructed as part of a collaborative project between University College London (UCL) and the UK National Physical Laboratory (NPL). The current swing-arm profilometer is intended as a proof-of-concept device and has the capability to measure concave and convex surfaces of up to 1 m in diameter with a minimum radius of curvature of 1.75 m for concave and 1.25 m for convex surfaces. Results will be traceable to national length standards. Principles of the swing-arm instrument will be described together with the mechanics of the arm design, its bearing and adjustment arrangements and surface probe options. We assess the performance requirements of 20 nm RMS form measurement accuracy in the context of the tolerances of the selected profilometer components, the error budget, and preliminary system measurements. Initial results are presented with a Solartron linear encoder. We also plan to mount optical sensors on the end of the arm as an alternative to traditional contact probes. Initially these will include an Arden AWS-50 wavefront curvature sensor and a Fisba μ-phase interferometer. The method of attachment of the Arden AWS-50 is outlined. The swing arm profilometer is to be located at a specialised facility, the OPtiC Technium, Denbigh, North Wales, where it will form part of a tool-kit of metrology and polishing devices for researching the production of large aspheric surfaces.

Large diameter, non-axisymmetric aspheric mirrors can be measured interferometrically using null correctors that employ computer generated holograms (CGHs). The testing of off axis segments for the new class of giant telescopes pose requirements that beyond the state of the art for CGHs alone. The long radius of curvature and the magnitude of the aspheric departure require other lenses and mirrors to be used along with the CGH. The alignment of these systems is very sensitive and the absolute accuracy of the alignment is critical to the system performance. We have developed techniques that use diffracted light from patterns on the CGH to accurately define the alignment of multi-element null correctors. We will present results from the null test of the 1.7-m New Solar Telescope primary mirror. The optical shape of this mirrors is an off-axis paraboloid from an f/0.7 parent.

The primary mirror for the 25-m Giant Magellan Telescope is made of seven circular segments, each of 8.4-m diameter. The lack of axisymmetry and the steep aspheric departure present significant technical challenges for the metrology. These segments will be measured interferometrically using a complex system of mirrors and holograms to give a null test with high spatial resolution. While analysis predicts this system will meet requirements, an additional set of measurements will be used to corroborate the principal interferometric measurement. The set of tests, including these alternate surface measurements, assures that all aspects of the mirror surface are measured completely and redundantly. The corroboration tests discussed in this paper are: Direct surface profile using metrology system based on a laser tracker, measuring low order shape errors Shear testing with full aperture interferometer, separating small scale errors in the null test from those in the mirror Slope testing with scanning pentaprism, measuring low order shape errors and sampling small scale errors

Meeting the science goals for the Large Synoptic Survey Telescope (LSST) translates into a demanding set of imaging performance requirements for the optical system over a wide (3.5°) field of view. In turn, meeting those imaging requirements necessitates maintaining precise control of the focal plane surface (10 μm P-V) over the entire field of view (640 mm diameter) at the operating temperature (T ~ -100°C) and over the operational elevation angle range. We briefly describe the heirarchical design approach for the LSST Camera focal plane and the baseline design for assembling the flat focal plane at room temperature. Preliminary results of gravity load and thermal distortion calculations are provided, and early metrological verification of candidate materials under cold thermal conditions are presented. A detailed, generalized method for stitching together sparse metrology data originating from differential, non-contact metrological data acquisition spanning multiple (non-continuous) sensor surfaces making up the focal plane, is described and demonstrated. Finally, we describe some in situ alignment verification alternatives, some of which may be integrated into the camera's focal plane.

We discuss the application of modern precision electroforming technology to the fabrication of multi-slit masks used for multi-object spectroscopy. Electroforming technology is capable of producing very accurate compound curved thin metal shells using nickel or nickel-cobalt material. The curved slit masks can be fabricated to conform to a curved focal surface of spherical, conic, or arbitrary shape. A variety of optical coatings including gold and extremely low reflectivity copper oxide can be applied to the electroformed mask substrate prior to cutting slits. Precise rectangular slits and apertures of arbitrary shape are readily machined in the nickel materials using a three axis YAG laser machining system.

LLNL has successfully fabricated small (1.5 cm² area) germanium immersion gratings. We studied the feasibility of producing a large germanium immersion grating by means of single point diamond flycutting. Our baseline design is a 63.4° blaze echelle with a 6 cm beam diameter. Birefringence and refractive index inhomogeneity due to stresses produced by the crystal growth process are of concern. Careful selection of the grating blank and possibly additional annealing to relieve stress will be required. The Large Optics Diamond Turning Machine (LODTM) at LLNL is a good choice for the fabrication. It can handle parts up to 1.5 meter in diameter and 0.5 meter in length and is capable of a surface figure accuracy of better than 28 nm rms. We will describe the machine modifications and the machining process for a large grating. A next generation machine, the Precision Optical Grinder and Lathe (POGAL), currently under development has tighter specifications and could produce large gratings with higher precision.

Multi-object instruments provide an increasing challenge for pick-off technology (the means by which objects are selected in the focal plane and fed to sub-instruments such as integral field spectrographs). We have developed a technology demonstrator for a new pick-off system. The performance requirements for the demonstrator have been driven by the outline requirements for possible ELT instruments and the science requirements based on an ELT science case. The goals for the pick-off include that the system should capable of positioning upwards of one hundred pick-off mirrors to an accuracy better than 5 microns. Additionally, the system should be able to achieve this for a curved focal surface -- in this instance with a radius of curvature of 2m. This paper presents the first experimental results from one of the approaches adopted within the Smart Focal Plane project -- that of a Planetary Positioning System. This pick-and place system is so called because it uniquely uses a combination of three rotation stages to place a magnetically mounted pick-off mirror at any position and orientation on the focal surface. A fixed angular offset between the two principal rotation stages ensures that the pick-off mirror is always placed precisely perpendicular to the curved focal plane. The pick-off mirror is gripped and released by a planar micromechanical mechanism which is lowered and raised by a coil-actuated linear stage.

An important phenomenon in astronomy is polarization. Polarization data has been used to trace interstellar magnetic fields in our galaxy as well as in radio galaxies via Faraday rotation. Spectrometers equipped with lasers to help remove the blurring effects of atmospheric turbulence have advanced the collection of data of the known universe and advanced theories on the physics of the early universe. In this paper, the processes and results will be presented for an absorptive polarizer covering part of the visible (VIS) to the near Infra - Red (IR) wavelengths. Linear polarizers are essential optical elements for many optical devices and systems that are used in astronomy, astronomical instruments, telecommunications, aerospace/defense, medical/biomedical etc. This patented all-glass polarizer has a polarization bandwidth of at least 400 nm and high contrast ratio and transmission over the wavelength range of (600 to 1100) nm. It is monolithic, hence free of epoxy, adhesive or optical cement. This state-of-the-art polarizer is an advance over current commercially available glass polarizers which range from (633 to 2100) nm but with a typical polarization bandwidth of only 80 nm. This new polarizer offers excellent optical properties, as well as high durability and consistency, which will provide several advantages and benefits over technologies such as birefringent crystals and polarizing dielectric thin films deposited on glass substrates. The applications for this polarizer include various optical measurement systems, instruments and devices such as polarimetry systems, spectrometers, ellipsometers, optical modulators, imaging systems, polarization dependent isolators and shutters.

The South Pole, especially the highest plateau Dome A, is the best place to locate telescopes in the world due to its compelling environment, such as dry air, low humidity, low wind speeds, low values of sky noise, etc. For this site, especially significant is its very clean air with the lowest concentration of atmospheric aerosols and its negligible artificial light pollution. But the air temperature in Dome-A is extremely low. The lowest air temperature is about 89 degrees below zero. On the other hand, Dome A is covered with deep snow. In order to build and operate a telescope at such low temperature successfully, some of the problems caused by low temperature should be considered and tested through experiments. According to the Chinese Antarctic 2m LAMOST-style telescope project, a conceptual design of tracking system for a 2 meter optical and infrared telescope fitting to operate at Dome-A, including axes structure, materials, drive systems, lubricant and feasible ways to install telescope will be discussed in this paper.

The yoke of an alt-az telescope should provide a stiff interface between the azimuth journal and the tube of the telescope. The stiffness of the yoke affects the performance of the telescope servosystem and its mass has an important contribution on the total weight of the telescope. Based on the design of the yoke of the GTC 10m telescope, a new configuration is analyzed in order to take advantage of the azimuth journal to increase the stiffness and reduce the weight of the yoke. The performance of this configuration is compared to that of the yoke of GTC.

The Gemini-sponsored WFMOS Feasibility Study investigated a wide-field, prime focus installation for the Gemini telescopes. As constructed, the Gemini design allows for multiple, interchangeable telescope top-ends, although this capability has never been implemented. Constrained by a particularly challenging top-end mass budget, we proposed a new top end specific to WFMOS, employing a carbon fiber reinforced plastic structure. An innovative, out-of-autoclave manufacturing process using balanced pressure and liquid heating and cooling enables high-specification, large CFRP structures to be constructed suitable for incorporation as fundamental parts of telescope structures. Advantages include low weight, enhanced overall telescope stiffness, and cost-effective construction with on-site final assembly. We describe the manufacturing process and the proposed top-end structure, as well as highlighting the advantages of this type of structure and material for large and extremely large telescopes in general.

The workshop test of mount drive for Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) was completed in June of 2005. Now the giant mount has just been erected on Xinglong station, and is due to test in the summer of 2006. LAMOST mount mechanism features friction drive on both axes, and oil pad is employed specifically for the azimuth. For further improving the tracking accuracy in worse surroundings some nonlinear phenomena in the drive chain have to be addressed. Moreover, external uncertainties on Xinglong site, wind buffeting in particular, could affect load variation on the drive. The control system parameters would change with time, thus eventually degrade the tracking performance. All these reasonable assumptions call for a more robust controller than conventional PID approach to cope with. This is where H-Infinity controller comes in. This paper focuses on the mount drive of LAMOST by using H-Infinity technique and comparison with the PID servo. The load disturbance rejection is discussed, as well as transmission rigidity improvement is analyzed. Study and simulation are done in Matlab. The model test in our friction drive lab is presented.

Direct drive motors are finding their way into telescope drive designs and have many advantages over more traditionally used friction and rack/pinion drives. They are implemented as curved linear motors custom made to the actual diameter required by the telescope design. Custom design is by definition a costly process and this paper discusses the possibility to use standard straight linear segments to approximate the curvature. Detailed analysis is given concerning differences in the electro-magnetic properties compared to a custom design motor.

With the development of large segmented-mirror telescopes, the segmented-mirror support technology has been researched and used widely and successfully. Besides the sub-mirror cell used to support single sub-mirror, the whole truss for supporting all the sub-mirrors also has been developed gradually. Different from the backup structure of radio telescope, the truss of optical segmented-mirror telescope needs not only huge spatial dimension but also high precision and long-term stability. In this paper, the spatial topology of truss and selection of node type have been introduced, at the same time, through the design and assembling of the primary mirror truss of LAMOST, some experiences have been also shared.

This paper summarizes the main aspects of the design and qualification test results of the secondary mirror mechanism for the VISTA Telescope. A design overview is presented, with detailed description of the main aspects of the system including the electromechanical part and the control system. Also a description of the test facilities and test methodologies is provided prior to the presentation and discussion of the performance test results.

Besides the increasing use of adaptive optics (AO) on modern telescopes, active optics (aO) are still of high importance to optimize Image Quality (IQ) for non-AO instruments and decrease the dynamic range needed for AO corrections. We will describe the design and operation of an optical alignment bench used to calibrate the aO models of the peripheral wavefront sensors. This setup is used to determine optical models in stable conditions in the laboratory and thus optimize wavefront correction on the sky. We will show results of this technique applied to our 2x2 Shack-Hartmann wavefront sensor used for tip-tilt-focus-astigmatism correction of all our non-AO instruments. We will also review some sub-systems performance monitoring tools and finally gauge the performance of active optics on the Gemini telescopes by analyzing the delivered image quality for various instruments.

In active optics systems obviously a fundamental role is played be the choice of polynomials to describe the primary mirror deformations. The well known Zernike polynomials are widely used because of their immediate interpretation in terms of optical aberrations. Nevertheless in an active optics correction system context, the choice of the so called "minimum energy modes" as the polynomials to represent the mechanical deformations is best justified by their derivation from mechanical properties. This is the approach followed for the 2.6m primary mirror of the VST telescope, to be hosted on top of the Cerro Paranal ESO observatory. The calibration forces to compensate a given amount of each aberration mode are computed and discussed.

This work deals with active correction of the aberrations in a telescope by moving the secondary mirror. A special attention is here dedicated to the case of a secondary mirror whose motions are controlled by a 6-6 Stewart Platform (generally called by astronomers simply "hexapod", even if this term is more general). The kinematics of the device is studied; an iterative algorithm to solve the non trivial forward kinematics problem is described.

The alignment of a telescope consisting of 2 or more mirrors with powered surfaces is critical to system performance. For on axis images, secondary mirror tilt and decenter both predominately produce coma, and therefore, either can be used to correct coma. Consequently, for systems that operate over relatively narrow fields of view, it is not necessary to differentiate between secondary tilt and decenter. However, for systems utilizing wider fields of view, correcting tilt with decenter (or decenter with tilt) can result in large aberration variation off-axis. Details of a technique for differentiating between secondary mirror decenter and tilt through the use of off-axis wavefront sensing, aberration calculation, and alignment sensitivity modeling are presented.

The Active Segmented Mirror is a key subsystem of the Active Phasing Experiment. The size of the ASM is 154 mm in diameter. It will be used to test new types of phasing sensors recently developed within the ELT design study supported by the European Union. To our knowledge it is the first time that such miniature active optics composed of hexagonal segments having 3 degrees of freedom with a resolution of the order of a few nanometers and a range of several micrometers is manufactured. The ASM is composed of 61 hexagonal segments called "modules". Each module is assembled, glued and integrated from standard (piezo-actuators) and custom-made (mirrors, mechanics) parts procured from industries. The ASM has been designed and integrated at the European Southern Observatory. Specifications, designs, assembly tools, hand work skills, electronics, software, control algorithms and test procedures are the field of competences required to obtain in the end a "plug and play" product. The concept of the ASM is tested and validated by a prototype version composed of 7 modules equivalent of the central area of the ASM itself. The design, integration and results of the ASM tests are presented.

Durham University's Centre for Advanced Instrumentation (CfAI) are currently prototyping key components for the KMOS and JWST NIRSpec Integral Field Units (IFUs). These next-generation IFUs will make extensive use of complex monolithic multi-faceted metal mirror arrays, which are fabricated by means of freeform diamond machining. Using this technique, the inherent accuracy of the diamond machining equipment is exploited to achieve the required relative alignment accuracy of the facets, as well as obtain the necessary optical surface quality for each individual facet, thus facilitating the integration and subsequent testing of these complex systems. The CfAI have pioneered the use of such arrays in the IFU for the Gemini Near-InfraRed Spectrograph (GNIRS IFU), which was installed at Gemini South in April, 2004. The requirements for the next generation of IFUs, however, demand a considerable improvement in the optical performance of these components, e.g. alignment accuracy of the facets, surface form accuracy and roughness. In our paper we briefly discuss the optical designs of KMOS and JWST NIRSpec IFU, and summarise the requirements on the optical components. We then present details of the diamond machining techniques employed to fabricate these highquality components and discuss the latest results from our prototyping activities, which demonstrate our capability of producing optical components that meet the demanding specifications.

Largely thermal considerations have led the James Webb Space Telescope (JWST) Mid Infra Red Instrument (MIRI) European Consortium to specify a CFRP hexapod with rigidised Invar endfittings and brackets to form the Primary Structure of the instrument. Each bracket incorporates a pair of orthogonal flexures to provide kinematic mounting to JWST. The principal alignment of the instrument, namely the placing of the Pick-off Mirror (POM) in the telescope frame, must be known and be trackable by a combination of measurement and prediction. Contributors to the alignment are many and various, but potentially great uncertainty lies with the use of a hexapod with field separable joints. In order to provide continuous measurement of the response of the Primary Structure hexapod to integration, g release effects and thermoelastic effects, we have installed a strain gauge array in proximity to the flexures. In this way, asymmetrical strains, inadvertantly introduced during integration, may be detected. The technology employed is that of optical Fibre Bragg Gratings (FBGs), which allow us to measure strains continuously from room temperature down to cryogenic temperatures, with a modest investment in temperature calibration. The strain array has been used during the integration and testing of the Structural Thermal Model of the instrument, and some data have been obtained regarding the utility and effectiveness of this technique in diagnosing sources of alignment error buildup. This paper describes the technology employed, the logic behind these measurements and experience with integration and calibration. Analysis, and the results of some tests, both mechanical and thermal, are presented and discussed.

This paper will discuss the details of the metrology associated with the integration and testing of spacecraft systems and scientific instruments at the NASA Goddard Space Flight Center (NASA GSFC). Specifically, this paper will outline the process for correlating theodolite autocollimation measurements with theodolite coordinate triangulation measurements, laser tracker coordinate measurements, photogrammetry camera system, and other coordinate measurement techniques. For theodolite autocollimation data, NASA GSFC developed a Microsoft Excel-based spreadsheet program to calculate the transformation matrices from reference cube pointing directions into spacecraft coordinates defined by physical features. The autocollimated image return from the mirrored faces of the reference cubes are measured relative to each other and define unit vectors that point in the direction perpendicular to the cube face surface. The roll, zenith, pitch, and yaw are calculated from the direction cosines of the unit vectors that define the directional pointing rotations around coordinate axes. The theodolite-based pointing vectors are then transformed to the spacecraft coordinate system. The Brunson Spatial Analyzer^TM coordinate measuring software program is used to analyze data from theodolites using triangulation on target positions, a laser tracker coordinate measuring system, a photogrammetry system or any other coordinate measuring system. All the coordinate data is tied into theodolite coordinate data by measuring common targets. To correlate theodolite autocollimation on cube faces to the point coordinate location data, one must first measure the test object with the Spatial Analyzer^TM theodolite triangulation coordinate system. From coordinate features, a spacecraft coordinate system is defined by the blueprint design. One of the Spatial Analyzer^TM theodolites is used as the primary reference for the auto-collimation measurements. This ties together the coordinate target point locations to the pointing directions of mirrored surfaces of cubes.

The Refractive Aberrated Simulator/Hubble Opto-Mechanical Simulator (RAS/HOMS) test facility previously located at Ball Aerospace Division in Boulder (BASD), CO will be relocated to NASA Goddard Space Flight Center (GSFC). This paper will highlight the metrology and test methods used to characterize the facility prior to disassembly as well as assemble and align the facility once it has been moved to GSFC. The HOMS portion of the facility simulates the mechanical latch mechanisms that hold an axial instrument in alignment with the Hubble Space Telescope (HST) optical path. Two sets of three latches must be aligned in position on the HOMS structure to match that of the two axial bays in HST. The RAS portion of the facility is a refractive optical system that simulates the aberrations in HST's optical telescope assembly. Each mount and lens must be properly aligned within the RAS system in order to accurately simulate the aberrations of HST's optical system. The optical axis of the RAS system must be brought into alignment with the optical axis of HOMS system. Photogrammetry, theodolite auto-collimation data, theodolite coordinate data, and laser tracker coordinate data were used to characterize the system prior to disassembly. The same data will be used to bring the RAS/HOMS system as close to the original alignment as possible.

The quest for maximum throughput in high energy astronomy instruments has influenced an increasing trend in spectrograph design toward closely packed mirror and grating arrays. Gratings have additional challenges to those required for mirrors and are evaluated separately in this study. Since these instruments typically operate above earth's atmosphere, grating arrays are subject to a launch vehicle environment. Packing gratings close together in a confined space decreases substrate thickness below traditionally accepted standards for maintenance of surface figure. The everpresent pressure to minimize mass in flight payloads drives substrates even thinner. The University of Colorado has performed a study of several methods that may be employed to make thin gratings. In this paper, some traditional techniques are compared to less conventional ideas for using thin substrates. Environmental effects necessary for flight applications are also folded into the analysis for each thin grating type.

The paper describes a 3-DoF translational (XYZ) mechanism for the main detector of the EMIR multi-object spectrograph, developed for the GTC telescope. This mechanism is designed for the cryogenic environment (77 K) and consists of a parallel manipulator with flexure joints, actuated by three identical and symmetrically located linear actuators.

Infrared instruments are generally operated at cryogenic temperature which causes a serious problem for the mounting of optical components. This is specially the case for complex dioptric systems where the optical quality is strongly dependant from the relative centering of the lenses. In the frame of the pre-design of the VLT high resolution and large field infrared imager (HAWK-I) a design using spring system has been intensively tested. The paper describes the test carried out in order to assess the thermal and mechanical behavior of the mount. A special technique has been used to accurately verify the conservation of the lens position from room temperature to cryogenic temperature.

There are many ways to achieve the positioning accuracy established from tolerance in a cryogenic environment. One method is an opto-mechanical design which stays aligned at room temperature and at liquid nitrogen temperature without modifications. This could be achieved using aluminium mirrors with thermally matched aluminium holders and optical bench, that isotropically contract at cryogenic temperatures. The design of holders should allow some adjustment of the optics positions to correct possible errors in the manufacturing of the optical bench and/or optical holders themselves, without precluding the isotropic contraction during the cooling to the working temperature. This work illustrates the last prototype of cryogenic mirror-holder developed in our laboratory. The mirror mounting is based on a set of six forces which pull the mirror against the tree orthogonal faces of a reference corner. Adjustments to the mirror alignment can be achieved by means of six aluminium micrometers. Here we describe the device and illustrate the test results.

X-shooter, the first 2nd generation VLT instrument, is a new high-efficiency echelle spectrograph. X-shooter operates at the Cassegrain focus and covers an exceptionally wide spectral range from 300 to 2500 nm in a single exposure, with an intermediate spectral resolving power R~5000. The instrument consists of a central structure and three prism cross-dispersed echelle spectrographs optimized for the UV-blue, visible and near-IR wavelength ranges. The design of the near-IR arm of the X-shooter instrument employs advanced design methods and manufacturing techniques. Integrated system design is done at cryogenic working temperatures, aiming for an almost alignment-free integration. ASTRON Extreme Light Weighting is used for high stiffness at low mass. Bare aluminium is post-polished to optical quality mirrors, preserving high shape accuracy at cryogenic conditions. Cryogenic optical mounts compensate for CTE differences of various materials, while ensuring high thermal contact. This paper addresses the general design and the application of these specialized techniques.

We describe the design and construction of a Variable-delay Polarization Modulator (VPM) that has been built and integrated into the Hertz ground-based, submillimeter polarimeter at the SMTO on Mt. Graham in Arizona. VPMs allow polarization modulation by controlling the phase difference between two linear, orthogonal polarizations. This is accomplished by utilizing a grid-mirror pair with a controlled separation. The size of the gap between the mirror and the polarizing grid determines the amount of the phase difference. This gap must be parallel to better than 1% of the wavelength. The necessity of controlling the phase of the radiation across this device drives the two novel features of the VPM. First, a novel, kinematic, flexure is employed that passively maintains the parallelism of the mirror and the grid to 1.5 μm over a 150 mm diameter, with a 400 μm throw. A single piezoceramic actuator is used to modulate the gap, and a capacitive sensor provides position feedback for closed-loop control. Second, the VPM uses a grid flattener that highly constrains the planarity of the polarizing grid. In doing so, the phase error across the device is minimized. Engineering results from the deployment of this device in the Hertz instrument April 2006 at the Submillimeter Telescope Observatory (SMTO) in Arizona are presented.

The LSST camera focal plane array will consist of individual Si sensor modules, each 42×42mm² in size, that are assembled into 3×3 "raft" structures, which are then assembled into the final focal plane array. It is our responsibility at Brookhaven National Lab (BNL) to insure that the individual sensors provided by the manufacturer meet the flatness requirement of 5 μm PV and that the assembled raft structure be within the 6.5 μm PV flatness tolerance. These tolerances must be measured with the detectors operating in a cryogenic environment at -100C in a face-down configuration. Conventional interferometric techniques for flatness testing are inadequate to insure that edge discontinuities between detector elements are within the tolerances because of the quarter-wave phase ambiguity problem. For this reason we have chosen a combination of metrology techniques to solve the discontinuity ambiguity problem that include both a full aperture interferometer and a scanning confocal distance microscope. We will discuss concepts for performing flatness metrology testing with these instruments under these conditions and will present preliminary results of measurement sensitivity and repeatability from tests performed on step height artifacts.

X-shooter is a new high-efficiency integral field spectrograph mainly dedicated to the spectroscopic follow up of the gamma ray bursts. X-shooter will operate at the Cassegrain focus of the VLT with an intermediate spectral resolution of ~5000, and will provide a very wide simultaneous spectral coverage, ranging from 320 to 2500 nm. The instrument consists in a central structure which supports three prism cross-dispersed echelle spectrographs respectively optimized for the UV-blue, Visible and Near-IR wavelength ranges. X-shooter will offer an image slicer based Integral Field Unit (IFU) designed to analyse a 1.8"x4" input field into 3 slices of 0.6"x4"and to align then on a 12" long slit. The principle of the IFU is that the central slice does not include any dioptre, the light is directly transmitted to the spectrographs. Only the two lateral sliced fields are reflected toward the two pairs of spherical mirrors and re-aligned at both ends of the previous slice in order to form the exit slit. We present here the IFU design developed at the Observatoire de Paris.

Immersion gratings machined in germanium have demonstrated excellent performance in the 8 to 13 μm band. The machining precision is adequate for use down 2μm, the short wavelength limit of germanium. Materials exist (Si, GaAs, GaP, ZnSe and ZnS) that could enable gratings to be made for near infrared and visible wavelengths. Work needs to be done to determine the optimal machining conditions. Commercial forms of these materials are optimized for other applications and may need some development to improve their performance at the shortest wavelengths. Current machining precision is adequate in most aspects. The surface figure of the groove facets (i.e. wavefront error) would need just over a factor of 2 improvement at the shortest wavelengths to maintain diffraction limited performance. The tolerance in random groove position error may be the most difficult to achieve.

We have fabricated several germanium immersion gratings by single crystal, single point diamond flycutting on an ultra-precision lathe. Use of a dead sharp tool produces groove corners less than 0.1 micron in radius and consequently high diffraction efficiency. We measured first order efficiencies in immersion of over 80% at 10.6 micron wavelength. Wavefront error was low averaging 0.06 wave rms (at 633 nm) across the full aperture. The grating spectral response was free of ghosts down to our detection limit of 1 part in 104. Scatter should be low based upon the surface roughness. Measurement of the spectral line profile of a CO₂ laser sets an upper bound on total integrated scatter of 0.5%.

Optical fibres have already played a huge part in ground based astronomical instrumentation, however, with the revolution in photonics currently taking place new fibre technologies and integrated optical devices are likely to have a profound impact on the way we manipulate light in the future. The Anglo Australian Observatory, along with partners at the Optical Fibre Technology Centre of the University of Sydney, is investigating some of the developing technologies as part of our Astrophotonics programme². In this paper we discuss the advances that have been made with infrared transmitting fibre, both conventional and microstructured, in particular those based on fluoride glasses. Fluoride glasses have a particularly wide transparent region from the UV through to around 7μm, whereas silica fibres, commonly used in astronomy, only transmit out to about 2μm. We discuss the impact of advances in fibre manufacture that have greatly improved the optical, chemical resistance and physical properties of the fluoride fibres. We also present some encouraging initial test results for a modern imaging fibre bundle and imaging fibre taper.

Volume phase holographic gratings (VPHGs) are becoming widespread dispersing elements in the modern spectrograph. Different materials can be used to make such gratings. We developed photochromic polymers based on a diarylethene unit that make VPHG suitable for observations in the near infrared region (1 - 2 μm) where the materials are highly transparent and show large modulation of the refractive index. This modulation was measured on films of different polymers by using spectral reflectance obtaining values of the order of 10^-2, These values are large enough to make efficient VPHGs if the thickness of the films are about 25 μm. The sensitivity of the photochromic polyesters was measured at 514 and 633 nm. Prototype of photochromic VPHGs were made by transferring a 600 l/mm pattern of a Ronchi ruling glass slide on a photochromic polyester film (4 μm thick) by using a green laser (543 nm, 30 mW). The grating was successfully transferred as shown by optical microscopy and by the diffraction pattern induced by a white light.

VIRUS is a planned integral-field instrument for the Hobby-Eberly Telescope (HET). In order to achieve a large field-of-view and high grasp at reasonable costs, the approach is to replicate integral-field units (IFU) and medium sized spectrographs many times. The Astrophysical Institute Potsdam (AIP) contributes to VIRUS with the development and testing of the IFU prototype. While the overall project is presented by Hill et al.¹, this paper describes the opto-mechanical design and the manufacture of the fiber-based IFU subsystem. The initial VIRUS development aims to produce a prototype and to measure its performance. Additionally, techniques will be investigated to allow industrial replication of the highly specific fiber-bundle layout. This will be necessary if this technique is to be applied to the next generation of even larger astronomical instrumentation.

Fiber tapers have the potential to significantly advance instrument technology into the realm of fully integrated optical systems. Our initial investigation was directed at the use of fiber tapers as f-ratio transformation devices. Using a technique developed for testing focal ratio degradation (FRD), a collimated light source was injected at different angles into various fiber taper samples and the far-field profile of the fiber output was observed. We compare the FRD present in the optical fiber tapers with conventional fibers and determine how effectively fiber tapers perform as image converters. We demonstrate that while silica fiber tapers may have slightly more intrinsic FRD than conventional fibers they still show promise as adiabatic mode transformers and are worth investigating further for their potential use in astronomical instruments. In this paper we present a brief review of the current status of fiber tapers with particular focus on the astronomical applications. We demonstrate the conservation of etendue in the taper transformation process and present the experimental results for a number of different taper profiles and manufacturers.