A uranium enrichment plant utilizing atomic vapor laser isotope separation technology is currently being planned. Deployment of the plant will require tens of thousands of commercial and custom optical components and subsystems. The plant optical system will be expected to perform at a high level of optical efficiency and reliability in a high- average-power-laser production environment. During construction, demand for this large number of optics must be coordinated with the manufacturing capacity of the optical industry. The general requirements and approach to ensure supply of optical components is described. Dynamic planning and a closely coupled relationship with the optics industry will be required to control cost, schedule,and quality.

Optical component specifications for the high-average-power lasers and transport system used in the Atomic Vapor Laser Isotope Separation plant must address demanding system performance requirements. The need for high performance optics has to be balanced against the practical desire to reduce the supply risks of cost and schedule. This is addressed in optical system design, careful planning with the optical industry, demonstration of plant quality parts, qualification of optical suppliers and processes, comprehensive procedures for evaluation and test, and a plan for corrective action.

Evaluation and testing of the optical components used in the atomic vapor laser isotope separation plant is critical for qualification of suppliers, developments of new optical multilayer designs and manufacturing processes, and assurance of performance in the production cycle. The range of specifications requires development of specialized test equipment and methods which are not routine or readily available in industry. Specifications are given on material characteristics such as index homogeneity, subsurface damage left after polishing, microscopic surface defects and contamination, coating absorption, and high average power laser damage. The approach to testing these performance characteristics and assuring the quality throughout the production cycle is described.

Hughes Danbury Optical SYstem successfully manufactured three sets of complex sample cells for the Space Shuttle PHaSE experiment. Each sample cell assembly consists of an F/.55 spherical lens and an F/.45 parabolic skirt. Each is manufactured to exacting fabrication, metrology, coating and assembly tolerances.

A new class of telescope is being built with primary mirrors as large as 8.4 meters in diameter and as fast as f/1. Fabricating the secondary mirrors for these telescopes has presented tough challenges because of their large sizes, up to 1.7 meter diameter; their aspheric departure of more than 300 microns; the required figure accuracy of a few tens of nanometers; and the fact that they are typically convex and difficult to measure. We have developed tools and techniques to meet these demands to produce secondary mirrors efficiently and accurately. A dedicated facility was constructed in the mirror lab that integrates a 1.8-m stressed-lap polishing machine with interferometric and mechanical measuring systems. This paper presents data from a 1.15-m secondary that was finished in our shop, and from two other large mirrors that are currently being fabricated.

This paper describes the process by which Hughes Danbury Optical Systems successfully manufactured a beryllium secondary mirror for the NASA Jet Propulsion Laboratory's IR Telescope Technology Testbed. The secondary was fabricated and tested using conventional methods. Fiducialization was sued to calibrate and remove all systematic errors from the Hindle test. Additionally, surface roughness and scatter were fully characterized.

Fabrication procedures employed for producing optical components for the laser interferometer gravitational-wave observatory are described and discussed. Two ultra-pure fused silica substrates, 250 mm diameter and 100 mm thick, were polished to very high surface quality and precision. One side of each substrate is flat with the other side having a very long concave radius of curvature of 6000 m. The performance of the Teflon lap technique in polishing both surfaces will be reviewed.

Metrology procedures for determining the power, astigmatism, low and high spatial frequency variations in the surface profile on flat and curved optical surfaces are described. The procedures are applied to the characterization of optics produced for the Pathfinder program of the laser interferometer gravitational observatory and demonstrate that in the case of low spatial frequency surface errors measured by optical interferometry, measurements to a resolution down to (lambda) /2000 are possible in the measurement of the standard deviation of surface variations.

To certify compliance with the exceptional surface figure requirements of the laser interferometer gravity observatory, Hughes Danbury Optical Systems developed a unique high-accuracy metrology capability consisting of a custom 12 inch phase-measuring interferometer and an absolute calibration algorithm. The interferometer was specifically designed to minimize systematic retrace, phase- modulation, and ghost reflection errors. The calibration algorithm extends existing three-flat methods by employing circular harmonic transforms. Using this capability, three flats were calibrated over a 200 mm clear aperture to an accuracy of better than (lambda) /1000 rms. Comparisons with published algorithms are presented.

A number of 150 mm apertures in 250 mm diameter plano- concave with departures from the nominal figure of a few nm were carefully tested using phase measuring interferometry and the data reduced using pixel based absolute testing techniques. We discuss some of the data reduction techniques used as well as the precautions taken to verify the accuracy of the result. After accounting for systematic errors introduced by interferometer imaging, we show that the surfaces can be characterized to a few nm peak-to-valley over spatial scales form the measurement aperture to a few mm.

Large, high power laser systems such as that being constructed by Lawrence Livermore National Laboratories for the National Ignition Facility require accurate measurements of spatial frequencies of up to 2.5 lines/mm over a 100mm field of view.In order to ensure accurate measurements of the parts, the test apparatus must be well characterized. The systems transfer function (STF) of the interferometer under development to perform these measurements was calculated by comparing the power spectra of measurements of known phase objects to their theoretical power spectra. Several potential problem areas were identified and studied. Of primary concern was the effect on the STF of the rotating diffuser and incoherent relay system employed in most commercial laser Fizeau interferometers. It was determined that such an arrangement degraded the transfer function beyond acceptability. The other major concern was possible inability to measure certain frequencies due to propagation between the test piece and alignment of the system optics.Use of strictly coherent imaging and small propagation distance between the test piece and return flat, the system transfer function could be kept at acceptable levels within the range of interest.

An optical testing instrument, the Eyeglass Image Quality Mapper, has been developed that maps the power, astigmatism, and modulation transfer function over the surface of a progressive addition eyeglass lens. This instrument models the manner in which the eye views different regions of the lens and is automated so that testing can be performed without supervision and in a reasonable amount of time.In this paper, we describe the concept development, final design, and use of the instrument.

We construct the modulation transfer function (MTF) measurement system of a LCD using a linear charge-coupled device (CCD) imager. The MTF used in optical system can not describe in the effect of both resolution and contrast on the image quality of display. Thus we present the new measurement method based on the transmission property of a LCD. While controlling contrast and brightness levels, the MTF is measured. From the result, we show that the method is useful for describing of the image quality. A ne measurement method and its condition are described. To demonstrate validity, the method is applied for comparison of the performance of two different LCDs.

Present paper reports the methods and the results of investigations of the optical system resolution. The limiting spatial frequencies are recorded on the photothermoplastic carriers (PTPC) in the real-time scale. The used PTPCs with a resonance frequency close to the expected boundary of the contrast-frequency response of an optical systems make it possible to record the images of different test-objects on the PTPC. This allows us to get the true data and rated values for the resolution both of the stock-produced lenses with the resolution about 300 to 500mm^-1 and the special ones with the resolution above 1000mm^-1.

A method for collimation test by utilizing various binary spiral gratings is developed in this paper. Detailed discussion has been focused on the means to improve sensitivity and the optimum tuning mode giving the extremum resolution is proposed. Experimental results indicate that this method is a feasible and promising one.

Glass-ceramics are composites consisting of glass and crystalline phases. We report a series of microgrinding and polishing experiments: our first goal is to correlate material mechanical properties with the quality of the resulting surface, determined by surface microroughness and surface grinding-induced residual stresses. Our second goal is to compare deterministic microgrinding and loose abrasive microgrinding in terms of material removal rates and resulting surface quality.

Precision grinding of optical components is becoming an accepted practice for rapidly and deterministically fabrication optical surface to final or near-final surface finish and figure. In this paper, a comparison of grinding techniques and materials is performed. Flat and spherical surfaces were ground in three different substrate materials: BK7 glass, chemical vapor deposited silicon carbide ceramic, and sapphire. Spherical surfaces were used to determine the contouring capacity of the process, and flat surfaces were used for surfaces finish measurements. The recently developed Precitech Optimum 2800 diamond turning and grinding platform was used to grind surfaces in 40mm diameter substrates sapphire and silicon carbide substrates and 200 mm BK7 glass substrates using diamond grinding wheels. The results of this study compare the surface finish and figure for the three materials.

Current literature is rich with information on the interaction between coolants and metals in metal working. This includes the study of optimum coolant velocities, nozzle positioning, and coolant formations. Very little information exists on the role of coolants in glass grinding. The CNC deterministic microgrinding machines at the Center for Optics Manufacturing utilize water based coolants to provide lubrication at the part/tool interface, to remove heat from the metal bonded diamond tool, and to help keep the tool surface free of debris. We show that the angle of coolant delivery and the coolant velocity do not affect the rms microroughness of a variety of glasses when ground at commercially relevant in-feed rates. We discuss a preliminary experiment utilizing a high pressure coolant delivery system.

A grinding wheel with fine abrasives is conventionally applied for precision grinding. In particular the precision grinding of brittle materials in the region of ductile mode chip removal is based on the fine abrasive with grain size of a few micron to sub-micron. This paper shows possibility of ultraprecision grinding with coarse abrasive wheel of grain size of over ten microns and also the precision grinding technology with coarse abrasive wheel can realize high productivity in precision riding of brittle materials. The key of the technology is dressing/truing of superabrasive wheel or control of height distribution of grain tops. The strategies on truing/dressing technique of superabrasive wheel is proposed and a example to be applied to technique is shown. The surface finish of 0.9 nm Ra is achieved for borosilicate glass ground with the metal bonded diamond wheel with number 800.

Bound abrasive grinding of optical materials with CNC machining equipment can achieve precise control over product configuration. For some materials and grinding geometries, however, there can be cases in which machine deflection is significant and this impacts the shape of the optical parts produced. This machine stiffness issue is associated with the relationship between the material removal rate an the applied normal load, as well as the tool deterioration process. A dynamic model to aid in keeping the process fully deterministic is presented. The validity of this model is discussed according to data collected from plano grinding of BK7 and sapphire with diamond cup tool with wide range of process parameters such as abrasive's grit size, workpiece size, infeed rate, tool dimension, and the level of glazing of the tools. Modifications and application of the model to an sphere grinding geometry is also presented.

In deterministic microgrinding (DMG) of glass optics with metal bond diamond abrasive ring tools, cutter marks are generated on the lens surface by the relative motion between the grinding tool and the work piece. The cutter marks for spherical surface generation appear as curves that follow contact lines between the abrasive ring tool and the work piece from the center to the edge of the lens. For DMG surfaces using a three tool process, individual cutter mark heights vary form approximately 5 to 100 nm with a variable spatial separation of from 0.1 to 3 mm along the circumference of the lines. The number of cutter marks generated for one revolution of the work piece is typically equal to the ratio of the tool RPM to the work piece RPM. In this paper we describe experiments designed to investigate the relationship between machine vibration characteristics and cutter mark generation and to identify process parameters that most strongly influence the generation of cutter marks. Machine vibration is monitored during grinding with accelerometers, positioned in the x, y, and z directions and located on the tool spindle. A fast Fourier transform (FFT) is used to identify the dominant frequency components of the machine vibration. The fine ground surfaces obtained with the machine are hen measured with interferometry and also analyzed with a FFT to identify periodic features. An experimental approach is employed to identify the microgrinding process parameters, such as tool speed, work piece speed, infeed rate, cutting edge bevel width, and dwell time that significantly influence the characteristics of the cutter marks. Process parameters can then be chosen to minimize cutter mark generation.

Conventional approaches to the correction of mid and high frequency errors in the fabrication of aspheric optical surfaces employ 'bridging effects' of large semi-flexible tools. However, these effects are difficult to quantitatively predict, and their use often results in the loss of low-frequency figure. An alternative approach uses established computer-controlled variable dwell techniques with small figuring tools to remove these errors in a highly convergent and predictable process. Technical requirements on the measurement, data analysis, and machine tolerances surrounding the use of tools less than 30mm in diameter are discussed. The correction of features as narrow as 12mm demonstrated.

The rapidly renewable lap is based on the simple concept of generating the figure needed in a lap substrate and then replicating it into a thin film slumped over the substrate. Based on this concept, we describe how efficient laps can be constructed for the lapping and polishing of crystalline, amorphous, and metallic surfaces.

Pad polishing is an efficient technique for polishing-out a ground surface and reaching a figure better than one wave, ready for completion with less than an hour on a planetary polisher. Recent work has shown success on 350 mm square parts; current work involves scaling the process to 1.4 meter diameter. For the 350 mm square piece of BK7, removal was one micrometer every 10 minutes. Polishing-out from a 5 micrometer grind took less than 3 hours, to a surface smoothness of one nm rms. Other tests verified that the pad leaves no unusual subsurface damage. Following completion on a pitch planetary polisher, surface finish is the same as obtained for conventional processing.

Magnetorheological finishing (MRF) is a subaperture lap, deterministic process developed at the Center for Optics Manufacturing. MRF can remove subsurface damage from an optical component while correcting figure errors and smoothing small scale microroughness. The 'standard' magnetorheological fluid for finishing of optical glasses consists of magnetic carbonyl iron and nonmagnetic cerium oxide particles in water. This composition works well for a variety of soft and hard glass types, but it does not perform adequately for certain single crystal materials and polycrystalline compounds used in IR applications. In this paper, we describe modifications to MRF and finishing experiments for LiF, ZnSe, CaF₂, AMTIR-1, ZnS, MgF₂, sapphire, and CVD diamond.

The microstructure of sapphire modulus of rupture bars has been examined before and after a high-temperature anneal using a variety of characterization methods, collectively described as 'advanced diagnostics'. These methods include the localized techniques of transmission electron microscopy, Raman spectroscopy and high magnification polarized light microscopy, as well as the global techniques of x-ray diffraction topography, polariscope and wave font analysis. Comparison of data before and after annealing indicate that no change has occurred in the long-range strain distribution or subgrain structure. However, changes in microstructure consistent with the motion of dislocations within approximately 100 nm of the surface were observed.

Precision optical fabrication is often influenced by surface stress introduced during processing. Various steps, such as lapping, grinding, polishing and coating, can influence optical figure and transmitted wave font in sapphire optics. The Twyman effect was used as a tool to measure the variation in stress form different processes and to investigate annealing treatments. Compressive stresses were generated by all fabrication techniques; however, the magnitude of stress varied considerably. The highest stress was generated during the transition from the brittle to ductile mode of removal; the lowest stress was observed during polishing with colloidal silica. Heat treatments were successful in removing machining stress from the parts. After heat treatment at 1450 degrees C, the remaining grinding-induced stress levels were too small to measure accurately.

During grinding operations successively 'finer' grinding tools and conditions are employed. Fine grinding serves to improve the surface finish of workpieces but is generally not capable of easily removing the larger volumes of material required initially. Thus, there is a well recognized link between surface finish and the ease of material removal. In this paper we examine this relationship in a quantitative fashion for some optical materials for which a suitable data base is available. Grindability is considered in terms of the volumetric removal obtainable as a function of the applied normal load. For single crystal sapphire ground with a wide range of tools/conditions, this grindability measure is found to correlate approximately with the cube of the workpiece roughness. Similar correlations between grindability and finish are also found in comparing data for different glasses/crystals ground under identical conditions. The origins of this behavior are discussed in terms of possible micromechanical and dimensional explanations. Finally, since ease of material removal and workpiece finish are related, normalization against the roughness is proposed as a means for making comparison between different grinding media/conditions.

Sapphire optical materials have limited index of refraction homogeneity. This homogeneity can limit the degree of transmitted wavefront error achievable with current, conventional optical finishing practices. Current practices can not typically compensate well for the localized inhomogeneities in the sapphire substrates resulting in limited transmitted wavefront values. Emerging transmitted wavefront requirements exceed those achievable with current practices. Hughes Danbury Optical Systems recently completed a successful demonstration program in which computer controlled polishing was applied to the fabrication of very low transmitted wavefront error sapphire window. This technique involves measuring the windows in transmission and then polishing them in localized areas to remove the wavefront errors arising from the material index inhomogeneity. The net effect of each localized correction is a high fidelity transmitted wavefront over each subaperture. In the demonstration completed, we stated with windows fabricated to the limit of current, conventional practices. Applying computer controlled polishing, the transmitted wavefront quality was rapidly improved by a factor of up to five over the starting value. These results not only satisfied emerging requirements, but the process also resulted in satisfying parallel requirements of extreme surface smoothness and scatter as defined by the bi- directional transmittance distribution function. This paper addresses the process developed, its results, benefits and applications.

Polycrystalline magnesium aluminum oxide, transparent from 200 nanometers to 6 microns, offers a unique combination of optical and physical properties. A superior dome and window material in respect to rain and particle erosion, solar radiation, high temperatures and humidity; it is resistant to attack by strong acids, sea water, and jet fuels. Although it had been qualified for, and designed into several advanced UV/visible/IR optical systems, production of hot-pressed Spinel was stopped at Alpha Optical Systems in 1993 by the parent company Coors Ceramics. Development efforts on cold-pressed/sinter/HIP Spinel at RCS Technologies are reportedly stalemated at the present time. Therefore, there is no known significant effort directed toward the development of polycrystalline Spinel. however, the author is in contact with both domestic and foreign laboratories which have expressed a desire to develop the technology for transparent Spinel. Renewed development may begin during calendar year 1997. Because of the apparent continuing significant interest in Spinel this paper will review the properties of Spinel and will compare the most significant properties of Spinel with sapphire and aluminum oxynitride. The limitations of competing manufacturing processes, will be mentioned. Grinding and polishing considerations will be reviewed in respect to maximizing optical and structural properties.

This paper describes a new, fast tool servo system designed for fabrication of non-rotationally symmetric components using single point diamond turning machines. A prototype device, designed for flexible interfacing to typical machine tool controllers, will be described along with performance testing data of tilted flat and off-axis conic sections. Evaluation data show that servo produced surfaces have an RMS roughness less than 175 angstroms. Techniques for linearizing the hysteretic effects in the piezoelectric actuator are also discussed. The nonlinear effects due to hysteresis are reduced using a dynamic compensator module in conjunction with a linear controller. The compensator samples the reduced using a dynamic compensator module in conjunction with a linear controller. The compensator samples the hysteretic voltage/displacement relationship in real time and modifies the effective gain accordingly. Simulation results indicate that errors in the performance of the system caused by hysteresis in the system can be compensated and reduced by 90 percent. Experimental implementation results in an 80 percent reduction in the motion error caused by hysteresis, but peak-to-valley errors are limited by side effects from the compensation. The uncompensated servo system demonstrated a peak-to-valley error of less than 0.80 micrometer for an off-axis conic section turned on-axis.

A new fabrication technique, derived from an earlier development to produce on- and off-axis optical surfaces of revolution is presented. Although based on a shape copying method, it is possible to generate different types of surfaces with the same machine tool. Load controlled point- contact machining is applied using a small tool which is guided along a pre-determined tool-path, not requiring an in-process tool-path control. This fabrication technique employs a self-correcting process and is characterized by an advantageous error propagation between tool and workpiece. The characteristics of this fabrication technique are discussed together with its application for the generation of on- and off-axis surfaces with conic sections as generators. The design of a first set-up for production of conic surfaces is presented with which it is possible to generate all kinds of conic surfaces on the same machine, featuring a pantograph enabling the production of different scales of the surfaces, together with the discussion of fist experimental data.

The effect of surface perturbations on Inertial Confinement Fusion target performance is currently being researched at Los Alamos National Laboratory. These perturbations can cause hydrodynamic instabilities which in turn reduce the targets' yield. To systematically measure the growth of these instabilities requires targets to be produced which have perturbations of a known amplitude and spatial frequency. We have recently assembled hardware onto one of our diamond turning lathes which enables us to machine and measure these sine waves in about 15 minutes. This is a significant reduction in time from the two and one half hours required by the previous method. This paper discuses the hardware, how it works, and how well the system is working for us to produce these targets.

One of Kodak's newest products required a low-cost, reasonably well-corrected, f/2.5 fixed-focus lens. We decided to use a plastic/glass hybrid lens that utilized both diffractive and aspheric technologies. The resulting two-plastic, one-glass element design has superior resolution. Manufacturing studies have documented that the lens will achieve high first-time yields. In this paper we discuss not only the prescription and its high first-time yield, but also system veiling in glare, relative illumination, and other diffraction-linked artifacts as they relate to electronic image capture.

We present results of iterative calculation, manufacturing and experimental as well as theoretical investigations of a novel diffractive optical element (DOE) which transforms a Gaussian TEM₀₀ input beam into a unimodal Gauss-Hermite complex distribution. The iterative calculation procedure is based on the application of the method of generalized projections. The projection operator onto a set of modal functions is implemented through partition of the focal plane into a 'useful' and an 'auxiliary' domain. As a result of this calculation there will be a 2D phase distribution which has to be transferred into the optical element. This element has been manufactured as 16 level surface profile by electron-beam direct-writing into a PMMA resist film and a subsequent development procedure of the resist. Each of the generated 15 steps of the resist profile corresponds to a certain electron dose, comparable to a usual 'isobathic process'. The final element consists of a fused silica substrate coated with the structured PMMA film, and has been designed for transmission mode and (lambda) equals 633 nm. Whereas computation results consist in the form of lateral distributions of the complex amplitude in the Fourier-plane, experimental results will be intensity distributions only. To measure additionally the phase distribution, we realized a special interferometric set-up. Both computational and experimental results are presented and demonstrate a good conformity with each other. Energy efficiency has been measured in the Fourier-plane as 37.7 percent, compared with the calculated value of 45 percent. The achieved results show good perspectives of such an approach for the formation and application of unimodal distributions.

Modulo-2(pi) phase elements calculated by relatively simple ray-tracing methods turned out to be suitable tools for laser beam profile homogenization under certain preconditions. As an example, we present results of the transformation of a Gaussian TEM₀₀-input beam with (lambda) equals 10.6 micrometers into a box-shaped intensity profile which has to be generate in the so called focal plane at a given distance from the element. The manufacturing of the investigated elements was realized by electron-beam lithography in combination with reactive ion etching. For computer modeling of the behavior of these elements a FFT- algorithm was used, working on the basis of paraxial approximation of the Kirchhoff-integral. The quality of achieved beam shaping depends of several parameters covering effects which are design-dependent, input-beam dependent, set-up dependent, or technology dependent. In an earlier paper we investigated the influence of varying beam waist diameter and beam waist position for a given element as well as of varying distance of the plane under investigation from the designed focal plane. In the present paper the interest is focused onto the influence of varying size of the element's clear aperture and of technologically caused deviations of realized step heights from the design values for the multi-level binary profile. Evaluation criteria were the lateral intensity distribution as well as the quantities diffraction efficiency and mean square amplitude deviation.

Prior to any interferometric surface shape testing, it is necessary to calibrate the interferometer in order to avoid systematic measurement errors. One common calibration method employs a standard specimen which has been previously calibrated by a so-called absolute testing method. Another method is the direct application of absolute testing methods to the interferometer. The authors have in the past developed and used absolute interferometric testing methods to calibrate flat, spherical and cylindrical surfaces, as well as complete interferometers. Now they have developed new methods, suitable also for toric and conical surfaces and the interferometers. The basic principles of the calibration methods are described. The correctness of the methods and the influence which measurement errors have on the results are demonstrated by computer simulation.

A method of interferometrically measuring large convex aspheres using test plates with computer generated holograms was developed at the University of Arizona. We present the results from a set of experiments that demonstrate the accuracy, flexibility, and the simplicity of performing the holographic test. A low-cost stand-alone setup as built for implementing this test on a 38-cm convex hyperboloid. A direct comparison of the CGH measurement with results from a classical Hindle test shows excellent agreement. We also demonstrate the unique attribute of this test to measure bare glass surfaces and highly reflective surfaces without making any modifications to the test equipment.

The modern Hartmann sensor provides a geometric measurement of wavefront as opposed to an interferometric measurement. Thus, it is free of some of the constraints of interferometry such as the requirements for vibration isolation, source coherence, and a reference source. Hartmann sensor configurations are presented which demonstrate the versatility of this technique while providing wavefront evaluation accuracy and sensitivity comparable to interferometry. There is a discussion of system alignment and operation as well as a discussion of software requirements.

Use of thin and segment's mirrors statement of a question about test in the process of manufacture, in unloading in a rim of apparatus or process of exploitation.

The quantitative determination of wave aberrations for high- quality imaging systems for off-axis use is an important challenge to modern optical measurement techniques. Several proposals in the conjunction with Twyman-Green interferometry and shearing interferometry will be made for this purpose. Two of these methods allow a reproducible and definitely quantitative alignment of the Twyman-Green set-up to be achieve. One method uses the point image for the positioning and the other that the front face of the Twyman sphere can be the first surface of a so-called adjustment system and that the Twyman sphere is in its correct position when the adjustment system reports that correct adjustment has been achieved. Another proposal concerns a shearing interferometer that consists of a combination of two conventional shearing interferometers and is capable of capturing the complete information about a wavefront by recording a single interferogram. Moreover a new method for quantitatively determining the shape of a wavefront from this interferogram will be presented, which requires nearly no a priori information about the shape of a wavefront to be calculated, leads to accurate results with high lateral resolution for relatively large shears, reconstructs the information inside the whole aperture, and requires much less computational effort than procedures hitherto known.

A shearing interferometer unit is proposed, which is capable of gathering the complete information about a wavefront by recording a single interferogram and which consists of a combination of two conventional shearing interferometers. With its capabilities it is predestined to be used as a tool for accurate measurements because it can be built as a solid unit without moving parts. This aim will be supported by a new method for quantitatively determining the shape of a wavefront from the difference between the wavefront and a laterally sheared copy which allows experiments to be performed with shears up to 20 percent of the width of the aperture. The method is based on filtering of the wavefront difference in the frequency domain with a transfer function specifically determined for this purpose. A novel window function is used to deal with the influence of the edge of the pupil. This method hardly requires any a priori information about the shape of the wavefront to be calculated. Furthermore, it leads to accurate results with high lateral resolution, reconstructs the information inside the whole aperture, and requires a much lesser computational effort than procedures hitherto known.

Phase-shifting interferometry measures surface height error by acquiring multiple interferograms. Analysis of these data is affected by the accuracy of individual measurements and the ability to compare subsequent measurements. The accuracy of individual measurements relies on producing constant phase shifts between the interferograms. Interferometric testing o large aperture telescope optics can be limited by vibration as the optical path difference increase. To minimize the effect of vibration, a series of interferograms would be acquired as quickly as possible. To accurately compare subsequent measurements, fiducials are used to provide registration. Accurate fiducial location is essential. This paper will describe the implementation of a high frame rate CCD camera and frame grabber system operating on an IBM PC compatible computer platform. This system quickly acquires a series of six consecutive digitized interferograms which are evaluated for proper phase shift before being reduced in a commercial phase-shift analysis program. The speed and storage advantages of the frame grabber also allow the system to produce a time- averaged fringe contrast map which enables fiducials to be easily an accurate located.

Phase shifting interferometry requires an intentional shifting of the relative phase between the reference arm and the test arm of fan interferometry. Vibration can lead to uncertainty in the relative phase difference with respect to time and result in erroneous surface measurements. We have developed a method for actively compensating for vibration using a closed-loop phase servo system. An essential feature of this is a high frequency phase measurement. The phase is modulated and the intensity variations are measured with a high sped photodiode and digitized. This information is processed by a DSP and a five step algorithm is used to determine the instantaneous phase. These high speed phase measurements are used in a closed loop phase servo to compensate for vibration and also allow for phase shifting interferometry. Test results with and without the vibration compensation will be presented.

The goal of this 24 inch phase shifting Fizeau interferometer design is to measure the wavefront of an optical window at Brewster's angle. There are two important requirements: a small wavefront slope error and a high optical resolution. To test the sample in transmission, each pencil of light returned from the RF must go back through the window from which it was previously transmitted. Therefore, the slope of the wavefront transmitted through the TF has to be less than a few arc seconds, especially for a long cavity length. For example, for a 2 meter round trip, a 5 arc second slope causes the beam to deviate 0.05 mm. For a 431-mm sample imaged onto a 1000 pixel array, a 0.05 mm displacement corresponds to a 0.116 pixel, which is negligible. However, when a 100 mm sub-aperture is imaged, a 0.05 mm displacement is significant. A shorter round-trip distance can effectively reduce the displacement. The deviations due to a 5-arc second wavefront slope is 0.12 pixel for 2-meter round trip in the full aperture and 0.10 pixel for 0.4-meter round trip in the sub-aperture imaging. Because the phase of the optical window is to be measured and not the amplitude or intensity, the MTF is ont suitable for evaluating the interferometer's resolution. A phase object was measured to determine the system transfer function. The fidelity of the measurement is required to be within 60 percent amplitude for a specified spatial frequency range. For example,for a sinusoidal phase object with a phase undulation of 0.01 wave p-v, the measured result should not be less than 0.006 wave. From theory, a phase object with a smaller phase undulation can be imaged with good fidelity. Because the wavefront slope and optical resolution requirements are very tight, to ensure the interferometer meets these requirements, theoretical errors were thoroughly analyzed and the design implementation was carefully studied.

Most commercial laser Fizeau interferometers employ a rotating diffuser on an intermediate image plane. The image formed on this plane is relayed to the detector using incoherent imaging, eliminating potential interference effects from elements after the diffuser. Systems requiring high spatial frequency resolution cannot employ the diffuser or incoherent relay system to the degradation they cause to the system transfer function.With strictly coherent imaging, however, nearly parallel optical elements such as the CCD cover glass will produce interference fringes. Though these elements are common path, fringes will be visible in the phase measurements unless one of several specific conditions are met. This paper explores the theory behind the formation of these fringes and examines cases where this error may be eliminated. Theoretical calculations are compared with actual measurements taken on a laser Fizeau interferometer. The errors evident in the final phase measurements may be minimized with proper coating of the system optics, sufficient wedge in the elements, or removal of the nearly parallel elements from the system.

Laser interferometers have been used widely in the optics and disk drive industries. Often the surface of the sample is either too curved to resolve the fringes or too rough to reflect the incident beam back into the interferometer. Illuminating at a graze incident angle effectively increases the equivalent wavelength, and hence the reflectivity, but the image of a circular aperture becomes elliptical. Lasers with a long IR wavelength seem to be the solution. However,the spatial resolution of the vidicon cameras is usually poor, and the image lag is often too long. These limit the accuracy of an IR phase-shifting interferometer. Recently, we have designed tow types of interferometers for 3.39 micrometers and 10.6 micrometers using an InSb array and a micro- bolometer array, respectively. These modern cameras have a high resolution and hence greatly extend the range of measurable material from a blank to a finished optics. Because the refractive index of the optical material at the IR wavelength is usually very high, the anti-reflection coating of the optics at IR is more critical than that at a visible wavelength. The interferometer's design, the resolution, the dependence of the fringe contrast on the sample roughness, and the measurement results of various samples are presented.

An imaging ellipsometer has been developed which employs phase shifting interferometry to characterize the ellipsometric parameters. A modified Michelson interferometer is used in conjunction with a Wollaston prism to generate two interferograms with orthogonal polarization states. Subtraction of the phases in the two interferograms yields the ellipsometric parameter (Delta) . The fringe modulation of the two interferograms is used to calculate the ellipsometric parameter (Psi) . The characterization of the average intensity of the interferogram is the largest contributor to the errors in the modulation. New algorithms for reducing the errors in modulation calculations for phase shifting interferometry are presented. The deign of the instrument, results of measurements and algorithms for modulation characterization will be presented.

THe experimental model of laser interferometer for measurement of absolute refractive index and thickness of optical media had been created and investigated. The interferometer allows to test both solid, liquid and gaseous media. The sample for measurement should be in a form of a plane parallel plate. The interferometer permits to measure the geometrical thickness of the plane parallel samples with interference accuracy, simultaneously with the refractive index measurement. The mathematical simulation of measuring process with PC has ben performed. The results of investigations of the interferometer precision possibilities are presented.

In quality control nondestructive techniques gain more and more importance. Holographic interferometry has the advantage of being very sensitive and can be used contactless for inspection of technical components. The interferogram contains fringes, whose pattern holds information about the surface deformation of a part subjected to the load. The load in case of deposited silicone oxide film is cased by stress produced different thermal expansion temperature coefficients film and silicone substrate. Change in stress in thin silicon dioxide films was observed using a high stability portable holographic interferometer using dimension stability test. Pattern recognition algorithm for synthesis of stress analyses map is reported. A stress relaxation phenomenon in this film thickness of 0.5 micrometers on Si wafer has been observed. Correlation of differential stress with initial flatness deviation of Si wafer has been discovered. The advantages of the proposed measuring technique and results are discussed.

A new metrology technique was developed for on-line tool misalignment detection. It is an image based metrology system. It measures surface slope functions from the captured reflected image off the test surface. The measured surface slope function is then used to determine the corresponding tool misalignments in the ring grinding setup for the Opticam surface generator. A prototype detection system was built and tested on-line in the Opticam machine. The experimental results are presented in this paper.

Absolute distance interferometry is a promising technology for comprehensive investigation of optical component parameters, including measurement of radii and thicknesses. In special interferometric schematics, it is applicable to measuring parameters of surfaces after grinding and can simplify null corrector design or eliminate its implementation for final testing aspherical surfaces. A universal method for precision length measurement, called 'excess fractions,' was proposed at the end of the last century to calibrate gauges. In this method, the interferometer compares an unknown distance with magnitudes of several wavelengths. The array which consists of the remainders of integer parts of the phase shift between the reference branch of the interferometer and the measuring distance, will be obtained. The proposed consideration of the 'excess fraction' method is based on the Chinese Remainder Theorem. It will be shown that the confidence interval of the obtained distance is equal to the confidence interval of the fractions. Consideration of the finite precision will make the method independent of which units will express, and provides the intervals of unambiguity of the method.

The paper proposes an absolute distance interferometry (ADI) system using the technique of heterodyne and superheterodyne detecting. A two wavelengths HeNe 633nm laser is employed to generate a long synthetic wavelength for measuring absolute distance. The characteristics of the heterodyne ADI system using AOMs are analyzed. The optical wave cross talk and poor wave front quality will decrease the performance of the heterodyne ADI system. By using the technique of superheterodyne and optical fiber, the performance of the new ADI system is improved. The common optical path and reference signal picking configuration in the interferometer eliminate the affection of air turbulence and problem form optical fiber effectively.

A frequency shift interferometer for absolute distance measurement using LD-pumped Nd:YVO₄, microchip laser is proposed in this paper. The LD pumped Nd:YVO₄ crystal microchip laser here is an external cavity laser. By modulating the voltage supplied to PZT, the frequency of the laser beam is modulated. A frequency shift interferometer using the technique of frequency-modulated continuous-wave is established. In this experiment setup a reference interferometer is used to compensate for the drift of the central frequency of the laser. The experimental results show that drift of central frequency of the laser affects the accuracy of the measurement a lot and can be compensated effectively. But influence from the drift of frequency modulation ratio tot eh accuracy can not be compensated.

The static response function f(x,y) of bimorph mirror is calculated with the algorithms of Gaussian iteration and Monte-Carlo, while the performance of bimorph mirror deduced by Kokorowski is described using Poisson's equation, which meets the Neumann boundary conditions. The Zernike polynomials are fitted separately with whole set of response functions which are taken as base functions. The optimization of bimorph mirror is considered for a given pattern and the low order aberrations. The effectiveness of correction is analyzed theoretically and experimentally. The optical performed is analyzed and tested thereafter.

A new type of phase-locked laser diode interferometer which uses self-mixing interference in the optical system is described. The self-mixing interference signal is obtained easily by the optical feedback or feeding back laser beam from the object to the laser diode. The interference signal can be detected by a photodiode which is in the package of the LD. Therefore, a beam splitter, reference mirror and external photodetector are not required, and a kind of interference signal is obtained by a simple optical system. But the signal is not the same as that which is obtained in a conventional interferometer. We used the phase-locked technique to measure the phase change in the self-mixing interference signal. This technique enables us to detect the displacement of an object. We describe our principle, experimental setup, and experimental results.

We have designed a nd built a phase-measuring LUPI interferometer to use pre-aligned custom CGH nulls for high accuracy figure metrology of deep aspherics. The CGH nulls operate in double pass, first producing an aspheric test wavefront and then recollimating the return wavefront. This eliminates any need to locate the CGH at an image of the test pupil THe CGH is common to both test and reference paths, allowing the use of photomask quality substrates. Tho enable the CGH-LUPI to test a wider variety of aspheres, we have designed and built a set of 100 mm aperture accessory optics for use in combination with CGH nulls. These accessory optics consist of five singles, each approximately F/3, which may be kinematically stacked in numerous combinations and permutations to produce test wavefronts ranging from nearly collimated to F/0.75 A CGH null compensates for asphericity of the test optic and design aberrations of the accessory optics. The interferometer and accessory optic designs permit independent verification of all aspects of system accuracy and calibration without the need for disassembly. Designing a custom CGH null involves raytracing the accessory optics but not the interferometer mainframe optics. Depending on the phase measuring algorithm selected, known system aberrations due to manufacturing tolerances may be software compensated in real time.

The manufacture of modern optical components often requires the se of high performance interferometers, usually based on phase-shifting techniques. However, there is currently no commercial phase-shifting interferometer having the capacity to measure large parts, such as those found in inertial confinement lasers and other large systems, with the required high spatial resolution. In order to circumvent the restrictions on the size of standard interferometers, we have designed and built a stitching interferometer for large plano surfaces, using a standard commercial 'small' diameter phase-shifting interferometer. The system is completely automated, using a PC computer to acquire and stitch measurements together to produce the original large surface. The advantages of this technique are low cost, small size, and preservation of spatial resolution. Also, smaller propagation distance means better handling of the smaller spatial periods. One such system has been in actual use for the characterization of large size mirrors since December 1994. In this paper, we shall look at the design of the system and produce, as an example, actual measurements performed on a PHEBUS laser slab polished more than a decade ago. The interferogram shows extraordinary features never seen before in such detail.

In this paper we describe an interferometric technique for testing uniformity in surface figure of large cylinder optics. In our laser scanning system, we employ large (1 1 inch) cylinder mirrors for focusing of laser beams over a wide scan range. Performance of the system depends critically on the uniformity of the beam size on the focal plane over this scan range. Departure of portions of the surface figure from the ideal cylindrical surface lead to varying beam size that limit the performance of our systems. Initially we tested these mirrors with a metrology technique that sample beam size on the focal plane at various scan positions. This technique is both time consuming and unreliable. To circumvent these limitations, we developed a fast interferometric technique to qualify these mirrors using a computer generated hologram (CGH) as our reference cylinder optics. The methodology employed simulates the scanning process by subdividing the interferogram of the cylinder mirror into small sections that are of the order of the beam size, analyzing the surface figure over these subsections and then computing a figure of merit (FOM) that is tied to the uniformity of the surface figure over the entire mirror. The correlation between the two independent measurements is found to be very good. In the following we discuss briefly the methodology developed in the Zygo platform, which can be easily implemented as an automated QA procedure.

We have developed a SHack-Hartmann system, which has been extensively used to test various telescope around the world over the past 5 years. In this paper we describe the instrument and the software, and indicate how they have been used to measure the optical aberrations in terms of coma, spherical aberration etc. We also show how our system can be used to identify less obvious problems like telescope support errors and dome and mirror seeing.