Current development of advanced optical technology in Institute of Optics and Electronics, Chinese Academy of Sciences is reported in this presentation. In advanced optical manufacturing technologies, the large astronomical telescopes, the large mirrors and the light-weighted mirrors are being developed in our Institute. The active manufacture technology of the large mirror is being carried on. In advanced optical testing technologies, we have developed a serial of Hartmann-Shack wavefront sensors used in this field. Furthermore, Adaptive optical technology has been developed and successfully applied in astronomical observation, ICF facility and high resolution retinal imaging of human eye in IOE, CAS.

The challenges for the first telescope designers were the polishing of lenses or mirrors, the pointing of them to the stars, and the tracking of the sidereal movement. The classical technologies, which they used, were spherical mirror polishing, passive, iso-static supports for the mirrors, and equatorial mounts with clockwork drives. The maximal sizes which they could achieve with these technologies, were 5 to 8m main aperture diameter. The practical limits in the sizes of the "mechanical" age were overcome with the upcoming of electronic control elements and digital computers. Now, giant optical telescopes in sizes from 10 to 100m are under construction or in planning. For these telescopes, beside the optical layout itself, the integrated system (= "mechatronic") approach to the structural, mechanical and control elements, which support the optical components, are a major issue for the final success of the projects. The talk will highlight some major aspects of this mechatronic approach, as system design, end-to-end simulation, control architecture for segmented mirrors, and on-site erection and commissioning, and will be supported by photos, sketches and diagrams.

Some results on active polishing technology for large aperture aspherical mirrors and ultra thin mirrors, which have been developed in recent years in Nanjing Institute of Astronomical Optics and Technology, CAS, are presented in this paper. There are two polishing methods developed for the large aperture ultra thin mirrors with two different trial mirrors respectively. One is a hexagonal mirror with diagonal size of 1100mm, and thickness of 25mm by no-separate support method specially for polish the sub-mirror of Schmidt corrector of LAMOST, which is a national large scientific project of China. Another is a circular mirror with 1035mm in diameter and 26mm in thickness by active support method. The active stressed polishing technology developed for large aperture aspherical mirror with fast f ratio, and a paraboloidal mirror with a diameter of 910mm and an f ratio 2 as was successfully polished. The computer controlled polishing is also different from the normal way in the system. Some complicated aspects were added. The results showed the final surface accuracy of all these trial mirrors is better than expected requirements for normal application in astronomical telescopes.

Extreme large optical telescopes will operate in an open environment and may be excited by wind effects. The position control of the mirror segments may need fast control, and the position actuators and the related control loops may be separated in a conventional slow, iso-static and a fast reaction-mass type system. There exists some experience with wind excitations of airborne telescopes, e.g. the Stratospheric Observatory for Infrared Astronomy SOFIA. The pointing control system of that telescope is equipped with several dedicated design features, as a vibration isolations system, a flexible body control system and an active mass damper system to handle excitations in different frequency ranges. These features may be transferred to the position control systems of segmented mirrors. The paper will give some system engi-neers recommendations for designing those systems.

The recent upsurge in the demand for off-axis and complex "freeform" optical surfaces is driving the development of novel processes for their fabrication. This paper focuses on recent developments of the Precessions CNC polishing process for freeform surfaces, including off-axis as a special case. First, the surface-prescription and metrology-data, and their relation to the data-input for the polishing machines, are considered. The relevance of consistent coordinate frames is emphasised. An outline of how the process can 'polish' a ground freeform part (improve the texture), and then 'figure' the part (reduce the form errors) is given. Specific experimental case-studies are then presented, illustrating the versatility of the process on different materials and forms. Recent work is included in which the process-speed has been moderated in order to remove tens of nanometres of stock material, rather then the more usual hundreds of nanometres to tens of microns as in the standard Precessions process. The relevance of this to improving the ultimate surface-precision that should be achievable by this method is described. As a final illustration, the potential of the process to the rapid fabrication of the hundreds to thousands of 1-2 metre class mirror segments required for extremely large telescopes is considered.

The new generation of Extremely Large Telescopes, may require the identification of new construction technologies, in order to improve the stiffness to weight ratio of the structure, to introduce higher damping while maintaining under control the construction and maintenance costs. The identification of new construction technologies and the consequent development of the materials used, may allow to obtain a leading technological instrument able to meet also the most extreme scientific requests, and able to adapt to the new requests that might be raised along the life of the telescope. The control of the weight of the structure is extremely important also for the dimensioning of the auxiliary structures such as drives, bearings, shafts, hard stops, counterweight, stow pins, hydrostatics support systems, etc., for energy management, and for the problems related to pre-assembly, disassembly in factory and erection on site. In this preliminary study we consider a light weight floating telescope structure made of composite materials and plastic foams.

This paper describes the test facility which will be used to perform optical quality and functionality test on the ESO VLT deformable secondary mirror (DSM). The last section will show a possible application of this method to manufacture and test large secondary convex mirror up to 8m diameter.

In the field of space flight, aviation and astronomy, R-C (Ritchey-Chretien) camera composed by two hyperboloid mirrors is one of the main instruments for detection and photography. A R-C system has been designed, which is composed of a primary mirror with clear aperture of Φ₀ = 600 mm, radius of curvature of 1440 mm, conic constant k₁ of-1.00486, relative aperture A₁ of 1/1.2, lightweight ratio of 53%; and a secondary mirror with clear aperture of 12-92 mm, curvature radius of 236.2 mm, conic constant k₂ of-1.66923. Therefore, the focal length of the R-C optical system is 6000 mm, and the relative aperture A is 1/10. Based on classical methods, the new testing methods have been developed. The R-C optical system has been tested by both classical and new test methods, the measurement results have been compared with a perfect agreement. The manufacture precision of the secondary mirror includes the spot diaphragm with a diameter of 0.02mm in size and PV 0.12λ (λ=0.6328μm) of wavelength. The spot diaphragm's size of the primary mirror is 0.02mm. The spot diaphragm's size of the system is 0.02mm, RMS is 0.18λ and PV is 1.2 λ measured by WYKO laser interferometer. Because it is used in infrared wave band, this optical system has already met the designed technical data perfectly. The R-C optical system has been checked and accepted by the user.

Extreme large telescopes, optical as well as radio telescopes have segmented mirrors and an active surface. The position control of the mirror segments may be based on a closed loop concept as used for optical telescopes, with a wave-front sensor for the identification of the mirror deviations; or an open loop concept as used for radio telescopes, with deformation sensors for the identification of deformations on the supporting structure. The paper compares the structural and mechanical components for the segment position control, the related control loop architecture, the placement of the position and deformation sensors, and the algorithms needed for designing the controllers.

In Space Solar Telescope, the decentering errors and air spaces between five components of collimating lenses are so small that subcell assembly method has to be adopted. This paper introduces a new method that can easily center lens with three small steel balls and some normal devices. The thought comes from traditional edging technology of lenses. When calibrating a lens, three precise steel balls will give the basis of positioning, After the optical axis of the lens is consistent with inner axis of subcell, the lens and the subcell are bonded together with some RTV adhesive. With all five subcells bonded with those corresponding lenses, they are assembled together again based on the outer reference surfaces that have been machined before. The precision of this method depends on the quality of steel balls and the parallelism of subcells. With the help of ZEMAX calculation, a collimating telescope is used to test the calibration error of the lenses. And steel balls are also introduced to quickly measure parallelism of subcells, and one interference graph of testing results is also presented.

The new frontiers of the research in the astronomic field require the use of more and more advanced high-performance structures. Only an adequate technological innovation of conventional telescopes and radio-telescopes allow to obtain structures able to meet the new specification of the projects. Besides, technological innovation is founded not only on the identification of more and more sophisticated mechanisms and optical instruments, but also on the development of new materials and manufacturing processes for the entire structure that constitute an instrument such as a telescope or a radio-telescope. Among these materials, the use of the carbon fibre is highly important. This material, which is already widely used in the aerospace and automotive fields, shall join also the astronomic field for ground instruments. Thanks to the experience acquired with instruments like ALMA, the industry of composites is now able to guarantee different solutions at relatively low costs that allow the instruments of new generation to move extremely important steps in the development of scientific research. Not just materials, but also processes, through which the materials are worked and manufactured, are extremely important. The use of technologies, such as hand lay-up vacuum bag, compression moulding, table rolling of composite tubes, filament winding, poltrusion and Resin Transfer Moulding (RTM), allow to identify the ideal solution both for big dimension objects, such as backup structure, main mirror structure of quadripod legs, and relatively small objects, such as actuators, adjusters system, etc. The wide choice, concerning the use of composite materials, and their techniques of production, allow the technicians to satisfy the exigencies of astronomers be they addressed to simple control of the weights or of the stiffness of the structures, or to specific thermal behaviour of the piece itself.

Some space-based telescopes have primary mirrors with great size which make active thermal control almost impossible. Sunshield is introduced to provide a relatively stable environment. Primary mirror's diameter is commonly several meters large and several millimeters thick such as in NGST or JWST. Even after segmented, it still could be one meter large. If temperature difference exists between two sides of mirror commonly with no heat source inside, great deformation could happen and then decrease performance of whole system. Theories to analyze deformation considering radius, thickness and material properties of mirror based on simplified models are proposed. Primary mirror is supposed to be spherical. Considering axial symmetry, only part of primary mirror is analyzed. To be convenient, thermal stress is converted to a moment by select proper thermal refercence. Most deformation caused by thermal stress can be seen as impacts of equivalent moment at both ends of selected part. Based on such hypotheses, analysis can be greatly simplified. At last, relationship between deformation and radius, thickness or material properties of primary mirror is given. To testify results, thermal deformation cause by thermal gradient along radius is also calculated using finite element method software: MSC NASTRAN/PATRAN. Considering axial symmetry, only 1/4 part of the segmented primary mirror is modeled. Fitful boundary conditions and temperature loads are also applied to it. Finally results from theoretical and finite element method were coincident. Simplified theories were proved to be accurate.

A method for minimizing the optical distortion from gravity sag on a suspended and autocollimated flat mirror facing ground has been proposed in the paper. Referring to this method, a mechanism consisting of 18 pulleys and weight sets unloads the gravity of the Φ1m flat mirror the alignment and testing benchmark of the 1m aperture optical system of the Space Solar Telescope (SST). Three positioning points support the mirror, allow the mirror to be held or suspended above an object to be viewed steadily and reliably. 18 pulling points on the back of the mirror unload the mirror's weight. The bonded joints of these 18 points are analyzed and tested to be reliable, and can bear the affection of variation of temperature and inner stress. The manufacturing and assembling precision of the support is analyzed and controlled, the unload forces of these 18 points are assigned. With this method, the surface error of the flat tested by Ritchey-Common arrangement is satisfactory for the alignment of SST of less than 1/50λ (RMS, λ=633nm).

The future large optical telescopes will have such large dimensions to require innovative technical solutions either in the engineering and optical fields. Their optics will have dimensions ranging from 30 to 100 m. and will be segmented. It is necessary to develop a cost effective industrial process, fast and efficient, to create the thousands of segments neeededs to assemble the mirrors of these instruments. INAF-OAB (Astronomical Observatory of Brera) is developing with INAF-Arcetri (Florence Astronomical Observatory) a method of production of lightweight glass optics that is suitable for the manufacturing of these segments. These optics will be also probably active and therefore the segments have to be thin, light and relatively flexible. The same requirements are valid also for the secondary adaptive mirrors foreseen for these telescopes and that therefore will benefit from the same technology. The technique under investigation foresees the thermal slumping of thin glass segments using a high quality ceramic mold (master). The sheet of glass is placed onto the mold and then, by means of a suitable thermal cycle, the glass is softened and its shape is changed copying the master shape. At the end of the slumping the correction of the remaining errors will be performed using the Ion Beam Figuring technique, a non-contact deterministic technique. To reduce the time spent for the correction it will be necessary to have shape errors on the segments as small as possible. A very preliminary series of experiments already performed on reduced size segments have shown that it is possible to copy a master shape with high accuracy (few microns PV) and it is very likely that copy accuracies of 1 micron or less are possible. The paper presents in detail the concepts of the proposed process and describes our current efforts that are aimed at the production of a scaled demonstrative adaptive segment of 50 cm of diameter.

The cryo-optical testing of the PLANCK primary reflector (elliptical off-axis CFRP reflector of 1550 mm x 1890 mm) is one of the major issue in the payload development program. It is requested to measure the changes of the Surface Figure Error (SFE) with respect to the best ellipsoid, between 293 K and 50 K, with a 1 μm RMS accuracy. To achieve this, Infra Red interferometry has been used and a dedicated thermo mechanical set-up has been constructed. This paper summarises the test activities, the test methods and results on the PLANCK Primary Reflector - Flight Model (PRFM) achieved in FOCAL 6.5 at Centre Spatial de Liege (CSL). Here, the Wave Front Error (WFE) will be considered, the SFE can be derived from the WFE measurement. After a brief introduction, the first part deals with the general test description. The thermo-elastic deformations will be addressed: the surface deformation in the medium frequency range (spatial wavelength down to 60 mm) and core-cell dimpling.

SCHOTT produces the zero expansion glass ceramics material ZERODUR since 35 years. More than 250 ZERODUR mirror blanks were already delivered for the large segmented mirror telescopes KECK I, KECK II, HET, GTC, and LAMOST. Now several extremely large telescope (ELT) projects are in discussion, which are designed with even larger primary mirrors (TMT, OWL, EURO50, JELT, CFGT, GMT). These telescopes can be achieved also only by segmentation of the primary mirror. Based on the results of the recent production of segment blanks for the GTC project the general requirements of mirror blanks for future extremely large telescope projects have been evaluated. The specification regarding the material quality and blank geometry is discussed in detail. As the planned mass production of mirror blanks for ELT's will last for several years, economic factors are getting even more important for the success of the projects. SCHOTT is a global enterprise with a solid economical basis and therefore an ideal partner for the mirror blank delivery of extremely large telescopes.

It is total different about structure of segment in stitching paraboloidal mirror and stitching spherical mirror or flat. Because of cuvature of the spherical mirror or flat is identical, even if in different points and different directions, so its surface appearance and external dimensions of all segments are identical too. But in paraboloidal mirror, its curvature radius is lengthening gradually, when the point deviates from apex to outer zone, even if in same point, its curvature is also different in different directions. When stitching all segments to an entire paraboloidal mirror, in order to make each edge curves of neighbouring segments keeping coincidence, all off-axis segments aren't regular hexagon, its external dimensions have slight variations. According to Dr. H. Martin's stitching pattern, if the maximum dimension of subsegment is 0.9M, the curvature radius of apex of paraboloid is 2.88M (the focal ratio of the entire paraboloidal mirror is near F/0.6), the author calculates the external dimensions of off-axis segment, its nearest optimum paraboloid, its nearest optimum sphere. On the other hand, the author analyzes the advantages and disadvantages about selecting which axis as rotative axis of off-axis segment under removal proceeding, for example selecting its normal line of center point of segment or its perpendicular bisector of segment in meridional plane. According to these analyses and calculations, this paper gives some suggestions and several sets of data about structure of off-axis segments. All these are just a base for further research in stitching paraboloidal mirror.

A new method has been developed to measure large aspherical mirrors accurately, quickly, and economically by using CMM (coordinate measurement machine). By using CMM to get the 3D coordinates of the actual points on the large aspherical mirrors and make bestfitting of actual surface and nominal surface, we can evaluate the surface of the large aspherical mirrors. It costs only 2 hours to measure an aspherical mirror with diameter larger than 1000mm. The results show good agreement with the results measured by Hartmann-Shack interferometer. Using this method, we can supervise the profile error to less than 5 μm PV during the grinding process. All the aspherical mirrors with dimensions within the range of the machine can be measured.

This article innovatively proposes a theory: The aim is to deform the ultra thin-segmented sphere mirror into aspheric mirror by applying forces on it. To reach this goal, this article focuses on the formation theory of aspheric surface, the theory of thin board in flexibility mechanics is, at first, applied to the study, and a model for calculating the stress of deformed aspheric surface is then put forward. Finally, theoretical calculation result gotten by this method is compared to that using finite element method. It is proved that the theoretical study of deformable mirror by applying force is right.

The 1m diameter paraboloidal primary mirror of the Space Solar Telescope, while in orbit, is positioned by three support points, and while in its vertical alignment on the ground, is unloaded by temporary supports of astatic lever and Hindle plate. It is crucial to confirm the unloading force in the support. It is also important to conduct the precision analysis of the unloading force. The relationship between the surface error and the unloading forces is founded from Hooke's law, among which the parameters and initial conditions are calculated by Finite Element Method. By the relationship, the optimized force value can be calculated by iterative operation, and the range of the unloading forces, which is the base of the precision analysis of the unloading support mechanism, can be also deduced. A precision analysis for the unloading support mechanism is given. Autocollimation tests show that the primary's surface error is less than 1/40λ (RMS, λ=633nm), which proves the analysis and ensures the diffraction-limited imaging of the telescope.

Challenges in high resolution space telescopes have led to the desire to create large primary mirror apertures. Ceramic mirrors and complex structures are becoming more important for high precision lightweight optical applications in adverse environments. Carbon-fiber reinforced silicon carbide (C/SiC) has shown great potential to be used as mirror substrate. This material has a high stiffness to weight ratio, dimensional stability from ambient to cryo temperatures, and thermal conductivity, low thermal expansion as well. These properties make C/SiC very attractive for a variety of applications in precision optical structures, especially when considering space-borne application. In this paper, lightweight C/SiC mirror prepared for a scan mirror of a high resolution camera is presented. The manufacturing of C/SiC mirror starts with a porous rigid felt made of short chopped carbon fibers. The fibers are molded with phenolic resin under pressure to form a carbon fiber reinforced plastic blank, followed by a pyrolization process by which the phenolic resin reacts to a carbon matrix. The C/C-felt can be machined by standard computer controlled milling techniques to any virtual shape. This is one of the most significant advantages of this material, as it drastically reduces the making costs and enables the manufacture of truly ultra-lightweight mirrors, reflectors and structures. Upon completion of milling, the C/C-felt preform is mounted in a high-temperature furnace together with silicon and heated under vacuum condition to 1500°C at which the silicon changes into liquid phase. Subsequently, the molten silicon is infiltrated into the porous preform under capillary forces to react with carbon matrix and the surfaces of the carbon fibers to form a density C/SiC substrate. The C/SiC material retains the preform shape to within a tight tolerance after sintering means the ceramization process is a nearly net shaping process. Reactive melt infiltrated C/SiC, followed by chemical vapor deposited silicon carbide (CVD SiC) cladding, is used to fabricate a 225-mm×165-mm ellipse mirror 18-mm thick and 0.41 kg weight. The mirror's backing structure contains hexagon "pockets". The individual ribs are only 2-mm thick, each contains a large cutout for structural efficiency and improves the mirror's thermal properties. Open back honeycomb lightweight structure is produced to gain 14kg/m² area density. CVD SiC has an excellent adherence to C/SiC. It also has an excellent thermal strain match. Approximately 150-μm of this material is used to clad the mirror substrate. The CVD SiC cladding is polished to be a super smooth surface with less than 0.372-nm RMS surface roughness. Experimental results indicate that reactive melt infiltrated C/SiC can be used as optical mirror substrates. Currently, experiments are under way to fabricate a large-scale lightweight C/SiC optical mirror in diameter larger than 600-mm.

Annular sub-aperture stitching technique has been developed for low cost and flexible testing rotationally symmetric aspherical surfaces, of which combining accurately the sub-aperture measurement data corrupted by misalignments into a complete surface figure is the key problem. An existed stitching algorithm of annular sub-apertures can convert sub-aperture Zernike coefficients into full-aperture Zernike coefficients, in which use of Zernike circle polynomials represents sub-aperture data over both circle and annular domain. Since Zernike circle polynomials are not orthogonal over annular dominion, the fitting results may give wrong results. In this paper, the Zernike polynomials and existed stitching algorithm have been reviewed, and a modified stitching algorithm with Zernike annular polynomials is provided. The performances of a modified algorithm on the reconstruction precision are studied by comparing with the algorithm existed. The results of computer simulation show that the sub-aperture data reduction with the modified algorithm is more accurate than that obtained with the existed algorithm based on Zernike circle polynomials, and the undergoing matrix manipulation is simpler.

Heat generated during polishing optical mirror surface is studied referring to tribology theory in this paper. The formula shows that the main factors of affecting heat generated include: rotating speed of polishing tool and mirror ω, load applied by polishing tool P, size of powder, and the material of mirror. Given the experiential value of parameters in the formula, heat generated by polishing are worked out. Based on the working-out result, thermal field, deformation and stress field of the polishing mirror are gotten by use of Finite Element Analysis software ANSYS. ANSYS's analysis shows the max deformation is 1.08μm on the being polished area.

Aluminum honeycomb mirror is an important component of the IR radiant cooler system employing in the aerospace applications. The radiant cooler system has a great impact on the quality of IR measurements. The quality of the mirror affects that of the radiant cooler. This article mainly introduces the manufacture of a large scale replicate mirror using thin film technology on a honeycomb-shaped aluminum plate. It discusses several technical difficulties, such as requisition of the mother board, selection of the glue and the techniques of replication on large scale aluminum plate. Borosilicate glass, which has low index of thermal expansion, is used as mother board material. It is requested to be processed to a good plane, N < or = -5, ΔN < or = 0.3.. After extensive experiments, the type of resin and solidifier and the ratio of those materials are confirmed. The selection is in consideration of the application in outer space condition and for the favor of processing big replicated mirror.

An experimental demonstration system of segmented SAO is built, which is a Cassegrin-type telescope, to demonstrate the segmented mirror technology, and the aperture is 300mm, F/number is 4.5. The primary mirror consists of three sub-mirrors, and each sub-mirror has five degrees of freedom. In order to get the diffraction limit in the wavelength of 632.8nm, ZYGO interferometer is used to sample the system's wavefront, and evaluate the performance. Although each sub-mirror of the experimental demonstration system has high precision surface figure, the difference of machining and the edge effects caused by change of environment and release of stress, makes the surface figure inconsistent, causes wavefront root-mean-square (RMS) value to become large, and badly affects the imaging. Based on the measurement and tolerance budget, other systems with 4, 6, 8, 24 and 36 sub-mirrors are simulated to analyze the requirements of the surface figure and misadjustment tolerance. Inverse limit sensitive tolerance evaluation is used to define the tolerance requirements and tendency. And the result shows that the sub-mirrors' number, configuration, location, precision, consistency and assembly should be considered and treated as a whole . And at the beginning of the system assembly, the sub-mirrors' surfaces figure must be measured to reassign the tolerance budget of the whole system.

With the development of space optical system, the technique of ultra thin mirror come forth and is paid more attention because of less difficulty in machining, low cost, lightweight, no disassembly during detecting and maintaining. The key technique takes advantage of deformation of ultra thin mirror as the influence of environment to adjust the surface figure. Its accuracy meets requirement. An analysis method is based on finite element analysis (FEA), and many items, including the amount of support points, the way of arrangement, the optimum design of support component are studied. The finite element method was used to analyze the mirror and some different mirror support schemes. The principal aim of the mirror analysis is to get numbers of support points and the ways of the support. There are three schemes including 12-6-1, 12-8-1 and 16-8-1models. Deformation of deadweight is calculated under the three conditions. The way of 16-8-1 is more suitable than the designs of other two. The support subassembly is amended to meet with the mirror surface RMS in the range of 30μm. Deformation of the mirror with support structure has been calculated. The result is 16.52nm, lower than a quarter of the wavelength, which indicates the feasibility of the support scheme applied to mirror. Theoretical result for the best way of support is presented. The result of analysis shows that requirement surface figure could be met through adjusting support points. It predicts feasibility of the support technique and provides theoretical value for active adjustment in the laboratory. At present, support and adjusting experiment of ultra thin mirror is being carried on.

According to the design requirements of a certain silicon carbide mirror, a parameter structure model of the mirror has been established using the finite element method. Then the sensitivity analysis and sizing optimization is applied to the eight structural parameters of the mirror and the optimum size is gained. The results have shown that the lightweight ratio of the optimum mirror is about 52.5%, and the WFE is satisfactory with the design requirements. Furthermore, the effects of different temperature levels, the axis and radial temperature gradient on the optimum mirror surface figure are also analyzed. It is also found that the deformation of the mirror is concerned with the magnitude and direction of temperature gradient directly.

Processing and compensating test of large convex spherical lens is a complicated problem for the time being. In this paper, based on the theoretical analysis and our practical experience of lens processing, a new processing technique and a null compensating test method, or called inner measurement, to the large caliber convex sphere is presented. This processing technique can effectively overcome the deformation in the influence of the gravity and support. Meanwhile this inner measurement can also overcome effectively the defects of the template method to the surface finish quality of the test elements and the problem of deficiency of the measurement aperture. This method can obtain high machining and measurement accuracies.

Based on genetic algorithm the design of lightweight mirror in a space optical system is presented. At present some novel lightweight techniques for more quick, more exact implementation of the lightweight mirror design are considered. The design of lightweight mirror is a multi-variable and multi-range of value complex discrete variable optimization issue which belongs to combination optimizations issue. Genetic algorithm (GA) has global astringency and parallelism, so employing it for the design of lightweight mirror can provide a global optimization solution. The theory of the method is genetic algorithm is used to be optimization subprogram, links with the finite element code by interface program, and the deformation of mirror surface is computed by emulation analysis while the weight reduction and the influence of dead weight to the deformation have both been taken into account. The lightweight mirror design is exact if the deformation is controlled under a certain tolerance, Pareto optimal solution gather of multi-variable indicating mirror parameters. An example is demonstrated for the lightweight primary mirror of an off-axis three-mirror system. The design objective is the root-mean-square optical surface error under the influence of dead weight satisfying the tolerance, which is controlled under one fortieth of wavelength. The approving deformation of mirror surface is gained by combining finite element analysis and GA, at the same time optimal solution gather about mirror design parameters is received.

Silicon carbide is a new type of optics material developed in recent years because it offered some advantages over other traditional optical substrate materials such as low density, low thermal expansion coefficient, high thermal conductivity, big special heat, big modulus of elasticity and potential cost and schedule. So in this paper, the silicon carbide space mirror was fabricated by both reaction bonded (RB) and chemical vapor deposition (CVD) process. The green body of the space mirror was prepared by silicon carbide powder, carbon powder, dilution and solidified agent using slip casting method. The space mirror blank was prepared by green body and pure silicon powder. They were laid in vacuum sintering furnace and sintered at 1500°C. In this temperature, silicon was melting then infiltrated in SiC green body and reacted with carbon to generate the new SiC, at the same time, bonded original SiC powder, in the end, the nonporous SiC/Si space mirror blank was fabricated. The reaction bonded silicon carbide (RBSiC) was consistent with original SiC powder, new generated SiC and unreacted Si. Because RBSiC was SiC/Si two-phase structure, the hardness difference between SiC and Si made the space mirror difficult to achieve precision optical surface by grinding. So a full density SiC thin film was coated on the surface of space mirror blank with RBSiC by chemical vapor deposition (CVD) process. The raw material was CH3SiCl3. The hydrogen (H2) was catalyst. The deposition temperature was 1300°C. The cooling rate could be controlled. The SiC space mirror was honeycomb open back lightweight structure. The honeycomb cellar could be triangle, rectangle, hexogen and sector. The biggest diameter of SiC space mirror blank which has been fabricated is approach one meter by forgoing process. In order to the forgoing process was feasible, a flat round SiC space mirror with 250mm diameter. The space mirror was composed of a 4mm thick round plane faceplate and hexagonal cellar honeycomb strengthen ribs. The 20μm thick SiC thin film was coated on the plate by CVD process. The microstructure of SiC was studied by metalogragh and scanning electronic microscope (SEM). X-ray diffraction showed that RBSiC was composed of α-SiC and Si, and the CVD-SiC was β-SiC.

This paper describes the optimum solution improving the total quality of the mirror room of the 2-m telescope. Referring to the mirror room with the dimetric truss, a group of reasonable sizes of the mirror room are given by optimization methods and modal analyses, which will improve the resonant frequency by 9.4%. As a result, the mirror room is less likely to resonate. Besides, the static module and dynamic response module in ANSYS are utilized respectively to analyze the mirror room deformation caused by gravity, the modal analysis and the vibration response. By the calculation of ANSYS, finite element analysis(FEA) method proves that the performance of the mirror room is greatly enhanced by means of optimum design.

With the development of science and technology, a primary mirror, whose diameter is over 2m, will be used. Thus, the conceive of ultra thin segmented mirror has emerged, and developing such a mirror has come to the forefront. Ultra thin mirror with thickness about 2-4mm is an important component of segmented optical system. In order to measure and adjust the mirror surface, it is necessarily important to unload gravity and support the ultra thin mirror in gravity field effectively. This paper describes the effect of supporting project on the surface of ultra thin mirror with FEM. The micro-shift of any supporting point will greatly effect the mirror surface for the ultra thin mirror. Thus it is necessary to choose appropriate form of FEM element which can be used to create the FEM model in high precision and to regularly arrange the node. The scheme makes it possible that the supporting points in the model are accurately shifted in correct direction. The precision of FEM model of the mirror is confirmed by computing and building the model with 20 nodes hexahedron elements. Its unload supporting structure is simulated with simple fixation model, and the effect of the supporting structure on two 500mm-diameter ZORODUR ultra thin mirrors, whose thickness is 2mm and 4mm,is analyzed. In their horizontal position in gravity field simulation, the RMS of surface can be limited in λ/30 (λ=632.8nm) with proper supporting structure. This aim can be achieved by using less supporting points in vertical position. As a conclusion, the difficulty of designing supporting structure and adjusting the ultra thin mirror surface can be minished in vertical position.

Optical system in the future will require primary mirror that push beyond the current state of technology for mirror fabrication. The mirrors will be very large and have low mass per unit area, and must maintain diffraction limited performance at the work surroundings. As a result, the conceive of segmented ultra thin mirror has been brought forward and are now in its research. We should develop primary mirror that has 2-4mm glass membrane which is attached to a stiff lightweight support structure through a set of actuators. In this paper, some analyse and computing simulation for active ultra thin mirror surface by using finite element method (FEM) are introduced:(1) simulating an ultra thin mirror with an aspect ratio of 250:1 by software "patran";(2) Computing the deformation of the ultra thin mirror supported by different supporting mode in its vertical position under gravity. The final supporting mode is selected and the result of optical surface accuracy of computer simulation is less thanλ/30(λ=632.8nm, RMS);(3) With the Zernike polynomials several low-order aberrations are got, which simulate the surface error after ultra thin mirror fabrication and the deformation because of change of work surroundings. After getting the influence function of single actuator, the actuators can be controlled actively and the supporting mode optimized, thus compensating the surface residual error caused by manufacturing and surroundings on computer simulation. The result of optical surface accuracy of the computer simulation is less thanλ/30(λ=632.8nm, RMS).

Mirror support system of astronomical telescope is composed of axial support and lateral support. In traditional telescope, because the contribution of lateral support to surface distortion is less than axial support, there are usually few lateral support methods such as lever counterweight, hydrostatic pressure and steel strap in the past. With increase of diameter to thickness ratio and use of strongly concave mirrors, lateral support is becoming more complicated and important than before. At the same time, application of segmented mirror make it impossible to support periphery of mirror, so, some new schemes have been designed to meet requirement of large segmented-mirror telescope. This paper introduces some classic and recent methods of lateral support for large telescope and gives some results of finite element analysis.

Computer Controlled Active Lap(CCAL) manufacture is a new manufacturing technology comparing the classical manufacture and Computer Controlling Optical Surface(CCOS) for large aspheric mirrors manufacturing. The removal function model of active lap is found based on the investigation of active lap structure and working features. After analysis the edge effect, we optimize the founded model through the method of pressure compensation. The mirror surface predicated by the optimized model above basically matches the mirror surface tested by Hartmann-Shack wavefront sensor during the experiments of Φ1300mm(F/2)aspheric mirror manufactured by active lap.

The Schmidt optical telescope system plays the most important role in telescope system for its large field of view while it is difficult to make the corrector used in this system1. In this paper, a manufacture and testing technology of Φ650mm are reported. Testing results are given

Optical synthetic aperture technology is a key technology in space optics. In order to make theoretical and application research on this technology in depth, an installment and adjustment system of high precision synthetic aperture has been designed. The paper mainly introduces the installment and adjustment system of primary mirror in optical system. The primary mirror is composed of three segment mirrors. Via the installment and adjustment system of each segment mirror, the primary one is synthesized. Segment mirror clamping mode is analyzed and clamping force is calculated, the maximum and minimum clamping forces are drawn, which make the surface figure deformable within the requirement range. An integrate analysis of the deformation of surface figure of segment mirror is also conducted and confirmed, which is caused by clamping force and temperature fluctuation and should be controlled below the wave length of 1/20. The segment mirror installment and adjustment system consists of 3 DOF translation platform and 2 DOF angle adjusting part. 2 DOF angle adjusting is realized by high precision screw thread pair driving flexible hinge, which ensures not only the simplicity, but also the stability and precision of the system as well. Experimental research is conducted on the flexible hinge and proves the rationality of the system. According to the test of the prototype, the translation resolution of the segment mirror installment and adjustment system reaches 0.2μm, the angle resolution reaches 0.5", which successfully satisfies the requirement of the synthetic aperture technology.