Proceedings Volume 8415

6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes

Proceedings Volume 8415

6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes

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Volume Details

Date Published: 1 October 2012
Contents: 4 Sessions, 52 Papers, 0 Presentations
Conference: 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies (AOMATT 2012) 2012
Volume Number: 8415

Table of Contents


Table of Contents

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  • Front Matter: Volume 8415
  • Session 1-1
  • Session 1-2
  • Poster Session
Front Matter: Volume 8415
Front Matter: Volume 8415
This PDF file contains the front matter associated with SPIE Proceedings Volume 8415, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Session 1-1
Thermodynamics research on optical system based on finite element method
Hao Yue Ming, Min Chen Hui
Thermodynamics researches have been carried out on the optical system in the detector in conventional munitions. First, temperature on the surface of the optical lens and the heat flux have been calculated with CFD method. Second, thermal strain of the optical lens has been simulated using ANSYS thermal analysis function. Finally, it arrives to the conclusion that the bigger the Mach number is, the higher the temperature and the severer the thermal strain will be. When the optical detector is moving with the speed of 2 and 3 Mach number, the aerodynamic heating is so serious that insulation measures should be taken to protect the optical system.
Analysis led design and optimization for large aperture mirror
Haifei Hu, Yingjun Guan, Ligong Zheng
Design method led by high precision finite element analysis (H-FEA) and structural optimization platform is provided to obtain the support and the configuration of large aperture mirror. Firstly the mirror’s abstract model, whose configuration depends on several geometric parameters, is drawn by CAD software. Then the H-FEA is carried out to get the adequate FEM model balancing precision and computing cost. Afterward optimization of the abstract model is implemented. Finally the mirror’s detailed model is drawn and optimized parametrically. All procedures and iterations are driven automatically in an integrated flow without manual interruption. A 1.5 meter aperture mirror design example, achieving λ/12 PV and λ/56 RMS (λ=632.8nm), shows the effectiveness and practicability of the method.
Comparison of optimization algorithms for adaptive optics system without a wavefront sensor
The adaptive optics system (AO) without a wavefront sensor produces an alternative tool to correct the aberrations where the wavefront distortions are hard to be measured directly. This kind of adaptive optics system optimizes an evaluation parameter directly relevant to the wavefront quality to achieve the wavefront correction, and the optimization algorithms determines the efficiency of wavefront sensor-less AO system. In this paper, several frequently-used algorithms covering hill climbing algorithm, genetic algorithm, simulated annealing algorithm and two hybrid algorithms, known as hybrid genetic-hill climbing algorithm and hybrid simulated annealing-hill climbing algorithm (SAHC), have been investigated to improve the correction efficiency. The correction speeds and correction effects of the five kinds of algorithms have been compared in simulations and experiments for an adaptive optics system with 19-elements unimorph deformable mirror. The results show that hill climbing algorithm has the fastest correction speed, but suffered from the local optimum problem. The other four kinds of algorithms can get good correction results and have similar correction effects. Considering the correction effect and correction speed comprehensively, SAHC is the most efficient optimization algorithm in the five kinds of optimization algorithms.
Parametric definition for the CGH patterns and error analysis in interferometric measurements
Computer-generated holograms are often used to test aspheric surfaces. This paper provides a parametric model for the CGH phase function using the exact geometric model. The phase function is then used to derive the sensitivity functions to alignment errors in testing. When using the CGH to test aspheric surface, it is important to separate the diffraction orders and only allow the desired order to pass the system. This paper also provides a recipe for determining the amount of carriers needed to eliminate the ghost images.
Research on eliminating high-order spectrum in broadband miniature spectrometer system
Kang Liu, Feihong Yu
A dispersion spectrum order distribution model is established in order to eliminate the overlapping of broadband spectrum range among various dispersion orders in grating devices and the micro-array detector based miniature spectrometer system. Both step filters and the numeric filter are, respectively, designed to eliminate the high-order spectrum in such system. For the step-filter method, a novel filter design is introduced. The evaluation function of the design parameters is defined. Two kinds of step-filter are designed and manufactured by lithography and thin film coating. For the numeric-filter method, a calculation method of deducing the high-order spectra data is illustrated. The accuracy of this method depends on the measurement of diffraction efficiency ratio. A new measurement method based on Deuterium-Halogen light source and short-pass filter is accomplished. Both Mercury-Argon lamp and Tungsten Halogen lamp are used to verify the effect of these two methods. And the results show that both methods have notable effects in eliminating high-order spectra of broadband miniature spectrometer systems. The step-filter method is a physical method and has an advantage of real-time input and output. The numeric filter is a calculation method that does not reduce the intensity of the spectrum. Currently, the numeric filter method can be seen to have certain advantages compared with step-filter method used in broadband miniature spectrometer systems with wavelength range of visible to near-infrared.
Session 1-2
Large field-of-view configurations for large-telescope adaptive optics systems: advantages and tradeoffs
In order to achieve high sky coverage with natural guide star adaptive optics systems, the reference stars need to be chosen over a large field of view. But the size of the optical beam can become unmanageably large in current and planned future giant telescopes. This can render the optics unaffordable. To solve this issue, we have adopted two approaches - multiple fields of view and star-enlargers - for the LINC-NIRVANA layer-oriented, multiple-conjugated adaptive optics system. In this paper, we compare and contrast the advantages and disadvantages of various optical configurations for wide-field, natural guide star acquisition on current 8-meter and future 25-40 meter extremely large telescopes.
Integrated modeling and optical jitter analysis of a high resolution space camera
Bowen Zhang, Xiaoyong Wang, Yongli Hu
The influence of jitter on the interface between space camera and satellite platform may cause the camera structural distortion, which will change ideal assembly and adjustment relationship of optical system, and affect the imaging quality. An integrated model of a high resolution space camera comprising reaction wheel assemblies disturbance which induced the largest jitter of spacecraft, structures and optics systems was developed in order to predict the expected dynamic performance of the camera in terms of MTF descending and image motion. The process as currently implemented uses Pro/Engineer for design, PATRAN and Hypermesh for model building and results visualization, NASTRAN for structural analysis, and Code V for optical analysis. A translator was developed in MATLAB to transfer PATRAN results to Code V optical analysis software. This jitter analysis results are used to assess image quality, improve the structural design, and mitigate the disturbance impact.
Measurements of the backscattering of ultrasmooth mirrors
Jingxian Wang, Ke Wang
In this paper we propose two schemes for measuring the backscattering of ultra-smooth mirrors, the principle of which is discussed detailed. The difference between the two schemes is also disclosed. According to the more sophisticated scheme we have built a practical apparatus, which has the precision and high efficiency advantage. The details of the design are presented. According to the backscattering amplitudes obtained using the apparatus, ultra-smooth mirrors have been divided into four groups. The statistical data has shown that the lock-in thresholds of ring laser gyros are correlative with the backscattering amplitudes of mirrors. Therefore the validity of the measurement is demonstrated. The method and the apparatus presented here can help the ring laser gyro (RLG) manufacturers in reducing the lock-in thresholds of RLGs.
Dwell time calculation for computer controlled large tool
Bin Fan, James H. Burge, Hubert Martin, et al.
The Computer-controlled Large-tool such as the stressed-lap which firstly developed in the Steward Observatory Mirror Lab (SOML) [1]and the Computer controlled active lap which developed in the IOE (Institute of Optics and Electronics, Chinese Academy of Science), those large tools are controlled by computer to manufacturing large optics, especially for grinding with loose abrasive and polishing with slurry. Comparing the fixed orbital lap, computer-controlled largetool can bend its lap surface timely to match the local sub-aperture, so it always strike the high area preferentially, due to its large diameter , computer-controlled large-tool possess highly remove efficiency and generate less middle-frequency and high-frequency errors comparing some small tools such as computer controlled optical surface (CCOS), but on the other hand how to calculate the dwell time for those computer-controlled large-tool becomes a challenge comparing those small tools. Based on the mathematical removal equation for computer controlled active lap we have none negative least square algorithm to calculate the dwell time, after the simulation, a optimized algorithm based on none negative least square is provided, the dwell time calculated by this optimized algorithm meet the wanted removal volume with little residual errors.
Development status of the prototype of the GMT fast steering mirror
Young-Soo Kim, Ju Heon Koh, Inwoo Chung, et al.
FSM is a secondary mirror of the Giant Magellan Telescope (GMT), which is 3.2 m in diameter. It consists of seven segments, each of which is 1m in diameter. The surrounding six segments are off-axis mirrors. FSM compensates image degradations caused by wind turbulence and structure jitter by using a tip-tilt mechanism. Korea Astronomy and Space Science Institute is developing a prototype of Fast Steering Mirror (FSM) together with four other institutions. The prototype is a full-size FSM segment, and it has two features; an off-axis mirror and a testbed for tip-tilt actuation. The off-axis mirror has the diameter of 1.06 m and fast focal ratio of 0.65. At present, lightweighting is successfully finished, and polishing of the front surface is proceeding. As for the tip-tilt, several test-beds have been assembled and the functions of tip-tilt have been checked. The third testbed is being integrated with a dummy aluminum mirror, three axial supports, a lateral support, and a test-bed frame. It is activated by a vacuum system. The test-bed will examine and verify the tip-tilt parameters. The FSM prototype is expected to be completed by 2012. In this paper, system engineering and progress of the prototype development are to be presented.
Error budgeting as applied to the design of the International X-Ray Observatory Mandrel Measuring Machine
Daniel C. Thompson, David H. Youden
This paper describes error budgeting as applied to the metrology for production control of a large number of ultraprecision X-ray telescope elements. The manufacturing challenge, a proposed metrology solution, and a detailed error budget demonstrating the feasibility of the proposed instrument design are described.
Poster Session
Design and optimization of push-pull-shear lateral support of thin meniscus mirror
Fu-lin Chen, Jing-xu Zhang, Xiao-xia Wu, et al.
Lateral support has a significant effect on the deformation of thin primary mirror. This paper deals with the analysis and optimization procedure on the “push-pull-shear” lateral support of thin meniscus mirror. Three steps were carried out in the lateral support optimization. Firstly a finite element model (FEM) was build for further analysis, then according to its structural characteristic, the ratio between the tangential force and the radial force was analyzed during the first optimization; In order to make the lateral forces with the same value, equal angle distance was changed to different angle distances during the second optimization, also lateral support position and magnitude of the lateral forces were given; during the last analysis, a portion of axial force was exerted at the inner ring, the response curve between the inner ring axial force and the RMS in Z direction of the mirror was plotted. The final result showed that the RMS value was decreased from 12.168nm to 3.253nm in Z direction. The optimization procedure provided a feasible way for lateral support of thin meniscus mirror.
A new method that indicates the peak stress of random vibration response
Yong Yan, Peng Xie, Zhen Xu, et al.

It is an important assessment targets that make a quantitative study of the peak stress of random vibration response during the mechanical properties design process of the space payload. Based on the equivalent of the destructive effect of the random vibration peak response and sine vibration response, the paper established the link between the two, obtained the sine vibration input function that equivalent to the destructive effect of the random vibration peak response. Considering the characteristic of the quantitative research that stress of sine vibration can be, the paper analyzed the stress of the sine vibration by the finite element method and indirectly accessed to the random vibration response peak stress which equivalent to the sine vibration destructive effect.

This method worked very well to indicate the peak stress of random vibration response during the ground random vibration tests. The paper provided an effective means of predictive and validation method for the mechanical properties design and test during the ground random vibration test evaluation. The developments costs of the engineering can be significant saving and greatly shorten the development cycle by the method of the peak stress of random vibration response indicated during the ground tests. It is also helpful to improve the safety and reliability of the space load structure in order to avoid the failure or fatigue of the ground random vibration tests.

Compute simulation of oscillation characteristic on plane matrix multiple coherence based on phase modulation
Ping Wang, Jin-hua Chai
Phase modulation of multiple coherence have important application foreground in electronic warfare. This paper is aimed at discussing the influence of the plane matrix multiple coherence on the oscillation characteristic of phase modulation. Because of its special background of application, we knew that the study of this problem hasn’t been reported. The similar study on the problem is coherent combining of fiber laser. The significance of phase modulation is to make the phase of every coherence unit time variation rule so that it can realize special purpose in actual application. When we set up the model of the numerical simulation, we take harmonic phase modulation for the sake of simplicity but to illustrate this problem.
Alignment technology of large telescope main optical system
Qi-rui Xu, Fan Wu, Ming Zhang, et al.
Optical alignment is very important in the commitment of a telescope. In this paper, the 2 meter class telescope of the Institute of Optics and Electronics, the Chinese Academy of Sciences is taken for example. The common alignment procedure and method of large telescopes are described, and the project method of getting better image quality in all the field of view is also included. The alignment procedure mainly includes the coarse alignment and the accurate adjustment. The method can be applied to the optical systems such as Cassegrain and R-C.
Designing of supports for a 1.2m active thin mirror
Ping Yao, Xuejun Zhang, Yudong Zhang
The support systems of primary mirrors usually consist of axial supports and lateral supports. The surface of an active thin mirror is maintained through actuators on back of the mirror. The axial and lateral supports are designed for a 1.2 m thin mirror with the aspect ratio of 24. The 36 axial supports are equally distributed on three rings and normalized radiuses are 0.275, 0.583 and 0.897 respectively. The numbers of axial supports for each ring are 6, 12 and 18 respectively. Three lateral support units are equally distributed at the outer edge of the mirror. The optimum surfaces are 2.7 nm and 12 nm RMS respectively when the mirror is mounted horizontally and vertically. It’s also demonstrated that the active supports could correct most of manufacture errors.
A novel large scale focal plane telescope using focal plane pointing method
Jianchun Lin, Liwei Sun, Chaoliang Yong, et al.

Large scale focal plane are required by a telescope due to wide field of view with high resolution. Since the detector technology could not accomplish the challenge requirement we developed a focal plane pointing method. This method consists of a pointing mirror and four array detectors.

The pointing mirror is placed between the optics and focal plane. As the mirror turns around the optical axis, the light from optics will be reflected to different direction where detector array is placed in the position of focal plane. The key techniques of this method are the pointing accuracy and stability of the pointing mirror and the flatness of the mosaic detector array. Our preliminary experiments indicate that this method is an effective and feasible way to get a large field of view and high resolution image.

Development of defects detection in gluing glass
Zongming Wu, Wei Yang, Tianquan Fan
The defects engendering in the process of glass gluing are mainly flaws and delaminations which will reduce the stability and processing availability of the optical component. How to detect these defects has become a technical problem for a long time. Several Non-Destructive Test (NDT) methods such as ultrasonic C-scan, bubble tester and infrared thermography are effective in inspection of it at present. In this paper, these three techniques’ detection principle, advantages and disadvantages are introduced. On the basis of detection demands, photothermal radiometry that it has become a powerful tool to detect subsurface defects in composites because of its non-contact and highly sensitivity is used to detect defects in the gluing process of glass for the first time. The basic idea that glass-layer transmits the spectrum and the spectrum energy is absorbed by glue-layer is also put forward creatively. By monitoring the temperature variation of glue-layer in time domain using infrared thermal imager, the defects can be discovered.
Measurement of an off-axis parabolic mirror using coordinates measurement machine and swing arm profilometer during the grinding process
Hongwei Jing, Changqing Lin, Bin Fan, et al.
We present the measurement methods for off-axis parabolic mirrors using Coordinates Measurement Machine and Swing Arm Profilometer during the grinding process. An off-axis parabolic mirror with 1200mm in parent focal length, 360mm in off-axis displacement and 410mm in diameter is measured using the methods introduced in this paper. The convergence curves of the surface error are reported, which is reduced from 204.7μm in PV, 55.3μm in rms to 1.1μm in PV, 0.3μm in rms after 39 iterations of grinding. Besides, the measurement methods are able to control the parent focal length and off-axis displacement to less than 0.1mm tolerance. An interferometric result is presented, which validates the measurement methods.
Thermal analysis of a 4m honeycomb telescope primary mirror
Jun Zhang, Hao Xian
Thermal characteristics of a 4m class honeycomb telescope primary mirror are presented. A 3 dimensional finite elements model of the primary mirror with the varying ambient air temperature as the boundary conditions is used for the numerical simulations. Every night’s air temperature profile has been detected in 2009 in Gaomeigu observatory site. Four typical nights’ air temperature profiles in different seasons are chose as the boundary conditions in finite element simulation. Temperature difference between primary mirror’s optical surface and ambient air is studied, as well as the axial temperature difference inner the mirror blank and radial temperature difference on the optical surface. Primary mirror seeing phenomenon results from the temperature difference between primary mirror’s optical surface and the ambient air is discussed. Thermal deformations due to temperature gradient of the primary mirror are analyzed by the finite element model. Axial thermal deformations on the optical surface are discussed in detail. Thermal deformation would induce the optical surface of primary mirror to distort from the normal shape, and lead to large observation image quality degradation. Primary mirror seeing with the turbulence near the optical surface would introduce wavefront aberration and deteriorate the final observation image. In order to reduce mirror seeing and thermal deformation, it is necessary to design a thermal control system for primary mirror. The thermal and structural analysis result will be valuable in designing primary mirror’s thermal control system.
Design of large aperture focal plane shutter
Jia-wen Hu, Wen-li Ma, Jin-long Huang
To satisfy the requirement of large telescope, a large aperture focal plane shutter with aperture size of φ200mm was researched and designed to realize, which could be started and stopped in a relative short time with precise position, and also the blades could open and close at the same time at any orientation. Timing-belts and stepper motors were adopted as the drive mechanism. Velocity and position of the stepper motors were controlled by the PWM pulse generated by DSP. Exponential curve is applied to control the velocity of the stepper motors to make the shutter start and stop in a short time. The closing/open time of shutter is 0.2s, which meets the performance requirements of large telescope properly.
The design for off-axis multimirror optical system with large field and small F number using coaxial assembly of two mirrors
Hui Liu, Shi-qiang Yan, Yun-tian Pei, et al.
The reflection optical system gets more and more attention nowadays owing to without chromatic aberration and small volume. The manufacturing and assembly/calibration technology for the coaxial reflection optical system is more mature relative to the other reflection optical systems. But the coaxial reflection optical system will obstruct the incidence ray especially when the field is large, which will reduce the energy entering the optical system and reduce the resolution. The off-axis Three-Mirror Optical Systems can conquer those disadvantages of the coaxial reflection optical system, however the manufacturing and assembly/calibration for the off-axis Optical Systems is very difficult which must use computer-aided technology. The manufacturing and assembly/calibration technology is the main bottleneck for the off-axis Optical Systems to the engineering application. The Author of this thesis researched the design theory of the Three-Mirror Optical System, and then schemed out off-axis Three-Mirror and Multi-Mirror Optical System smartly using coaxial two-mirror optical structure which conquers the disadvantage of small field and possesses of the all advantages of the coaxial reflection optical system. This new optical system has two mirrors, one of which is a parabolic mirror with high-order aspheric term and the other is a hyperboloid mirror with high-order aspheric term. The characteristics of this new optical system are as follows: the F Number is 1.25, the field of view is 2°×2° and the total length is only 115mm with coaxial assembly of the two mirrors.
Restoration of observed image with an unknown space-variant blur from wide-field telescope
Chaolan He, Honggang Wei, Mangzuo Shen
The field-of-view (FOV) of wide-field telescope is mostly beyond the scope of isoplanatic angle. Though the aberrated wave-front within a limited range close to guide star could be corrected accurately by adaptive-optics (AO) system, the image quality of object region deviation from guide star is dropped severely. The post-processing technique to restore degraded image observed from wide-field telescope is a good compensation for the limit of AO system. Restoration method of space-variant point spread function (PSF) degraded image which are used to overcome the turbulence-induced anisoplanatic effect, can improve image quality in the whole field of view of wide-field telescope, and restore image resolution to optical diffraction-limited level in free space. A multi-frame blind deconvolution restoration algorithm based on image sectioning method is presented here. The image is divided into several subimages, where the PSF of each subimage is assumed to be space-invariant. The conjugate gradient optimization algorithm based on maximum likelihood estimation (MLE) in space domain is adopted to estimate the space-invariant PSF and object information in each block. In order to reduce blocking artifacts at the subregion boundaries, larger, overlapping subregions as well as the Mumford- Shah regularization are used, and then the restored sections are extracted from their center. The resolution of the restored image using 5 satellite model blurred image frames through image sectioning method is enhanced significantly, compared to the space-invariant PSF restoration approach. There are more details about the original object, and it shows the proposed algorithm is valid.
Thin-film thickness measurement method based on the reflection interference spectrum
Li Na Jiang, Gao Feng, Zhang Shu
A method is introduced to measure the thin-film thickness, refractive index and other optical constants. When a beam of white light shines on the surface of the sample film, the reflected lights of the upper and the lower surface of the thin-film will interfere with each other and reflectivity of the film will fluctuate with light wavelength. The reflection interference spectrum is analyzed with software according to the database, while the thickness and refractive index of the thin-film is measured.
LINC-NIRVANA: cryogenic optics for diffraction limited beam combination
LINC-NIRVANA is an interferometric imaging camera, which combines the two 8.4 m telescopes of the Large Binocular Telescope (LBT). The instrument operates in the wavelength range from 1.1 μm to 2.4 μm, covering the J, H and K-band, respectively. The beam combining camera (NIRCS) offers the possibility to achieve diffraction limited images with the special resolution of a 23 m telescope. The optics are designed to deliver a 10 arcsec × 10 arcsec field of view with 5 mas resolution. In this paper we describe the evolution of the cryogenic optics, from design and manufacturing to verification. Including the argumentation for decisions we made in order to present a sort of guideline for large cryo-optics. We also present the alignment and testing strategies at a detailed level.
Finite element analysis of lightweight active primary mirror
Wei Xin Lu, Chun Lin Guan, Chang Hui Rao
With the increasing requirement on spatial resolution to achieve ideal performance in space-based optical imaging system, there is a need to enlarge primary apertures. However, primary mirrors of such systems cannot maintain its optical tolerances across the mirror surface after sending to space, because of gravity change and varying ambient temperature. It necessitates active optics technology of primary mirror surface correction. Since mass-to-orbit is expensive and limited, lightweight primary mirror is needed. The paper investigates a lightweight, active primary mirror. This primary mirror structure includes lightweight face sheet and substrate with surface-parallel actuators embedded in the recess of web support ribs. Finite element models of lightweight, active primary mirror structures with different structural parameters are established and simulated. Using the response function matrixes acquired from finite element analysis, the fitting errors for Zernike polynomials are computed by MATLAB. Correctability comparisons of lightweight, active primary mirror structures with different parameters are carried out. To get best correctability, the mirrors should have small recess depth, high and thin ribs, thick face sheets and long actuators. The structural analysis result will be valuable for the design of lightweight, active primary mirror.
Design of automatic leveling and centering system of theodolite
Chun-tong Liu, Zhen-Xin He, Xian-xiang Huang, et al.
To realize the theodolite automation and improve the azimuth Angle measurement instrument, the theodolite automatic leveling and centering system with the function of leveling error compensation is designed, which includes the system solution, key components selection, the mechanical structure of leveling and centering, and system software solution. The redesigned leveling feet are driven by the DC servo motor; and the electronic control center device is installed. Using high precision of tilt sensors as horizontal skew detection sensors ensures the effectiveness of the leveling error compensation. Aiming round mark center is located using digital image processing through surface array CCD; and leveling measurement precision can reach the pixel level, which makes the theodolite accurate centering possible. Finally, experiments are conducted using the automatic leveling and centering system of the theodolite. The results show the leveling and centering system can realize automatic operation with high centering accuracy of 0.04mm.The measurement precision of the orientation angle after leveling error compensation is improved, compared with that of in the traditional method. Automatic leveling and centering system of theodolite can satisfy the requirements of the measuring precision and its automation.
Integrated optimum design for a honeycomb mirror
Jin-long Tang, Shao-bai Wang, Jun Zhang, et al.
For a large aperture astronomical telescope, it is difficult to get the best performance design because there are so many design parameters need to be optimized. In the past, the optimization was carried out for each design parameter individually and the cross impact of different design parameters was neglected. To solve this problem, integrated optimum design was adopted to identify the interaction between parameters and to obtain an approximate explicit function by fitting those calculated design points, so the best design point can be determined. In this paper, an integrated optimum model was established to quest the optimized design of a honeycomb mirror. The individual and interactive impact of design parameters to the mirror’s surface error were analyzed based on this model. Through the optimized integrated design, the weight of mirror had been declined from 109.1 Kg to 74.1 Kg with a little increase of the mirror surface error.
Herschel Space Observatory Telescope characterization with Hartmann wavefront sensor
Guillaume Dovillaire, Yong Wang, Rémy Toth, et al.

The Herschel Space Observatory Telescope is the first of its kind to cover the 60-670 μm far infrared spectral band. Its optical characterization, performed in the visible range, was a true technological challenge requiring very large dynamic range coupled to very high accuracy. A specific Hartmann Wavefront Sensor (HWFS) was designed to meet the demanding specifications of the measurement.

The metrological system used by the EADS Astrium team to characterize the silicon car-bide based telescope will be presented as well as the main features of the specifically developed HWFS. The large expected wavefront error was measured in a double path set-up using the HWFS positioned in an extra-focal plane and a point source in the focal plane. The auto-collimation was carried out thanks to several liquid mirrors covering the M1 pupil plane and located in the conjugation plane of the HWFS sub-apertures.

The results on the wavefront error obtained at the Centre Spatial de Liege (CSL) in Belgium will be shown as well as the simulated Point Spread Function to be compared to the real PSF obtained during on flight measurements. The thermally induced focal length variations are also presented as the telescope is meant to operate at 70°K in space.

Real time controller for 37-element low-order solar adaptive optics system at 1m new vacuum solar telescope
Lei Zhu, Naiting Gu, Shanqiu Chen, et al.
A low-order solar adaptive optics (AO) system had been successfully built and installed at 1m New Vacuum Solar Telescope (NVST) of Full-shine Lake Solar Observatory. The real time controller (RTC) of the AO system, which consists of a correlation tracker and a high-order wavefront correction controller, was developed. In this system, the absolute difference algorithm is used to detect wavefront gradients. A new architecture with field-programmable gate array (FPGA) and digital signal processor (DSP) for the real-time controller based on systolic array and pipeline was designed. The controller was integrated into the AO system and saw the first light on February 24th, 2011, using solar granulation as the beacon. Later, the AO-corrected high resolution sunspots images were obtained using sunspots as the beacon. The observational results show that the contrast and resolution of the solar images are improved evidently after the correction by the AO system. The design of the RTC and the observational results will be presented.
Simulation result of multi-conjugate adaptive optics system based on minimum mean square error approach wavefront reconstruction
Currently, the multi-conjugate adaptive optics is one of the most promising concepts for large field of view adaptive optics compensation. The minimum mean square error (MMSE) approach is the main method for its wave-front reconstruction. In this article, firstly we briefly present the principle of three-dimension wavefront reconstruction; then the precision between the least square error (LSE), widely used in conventional adaptive optics, and the MMSE is compared by numerical simulation. We also did the study on the number of guide stars required to achieve a fixed field of view in different telescope aperture. The results show that the MMSE is more precise than LSE approach when the noise is considered; and more guide stars are needed for small aperture telescope. Finally, the system performance with different number of the guide stars for small aperture telescope is discussed.
Adaptive filter and linear quadratic Gaussian/loop transfer recovery compensator combination control of a non-linear tip-tilt mirror
Youming Guo, Xiaoyu Ma, Changhui Rao
Adaptive control of a tip-tilt mirror requires precise model estimation, which is difficult for the nonlinear features of piezoelectric actuators such as creep, hysteresis and resonance. A linear quadratic Gaussian control/loop transfer recovery (LQG/LTR) based compensation of the non-linearity is used, which employs a high sampling frequency position sensor to measure the displacements of the tip-tilt mirror and feedbacks the modified command needed to make the actuator response linearly to input command. A normalized LMS adaptive filter whose gains are adjusted by weight updating algorithm to minimize the mean square error of the output is used in order to reduce the jitter introduced by kinds of broadband and narrowband disturbance. The principle of an adaptive filter and LQG/LTR compensator combination control of a nonlinear tip-tilt mirror is introduced. The method is compared with the integrator and LQG/LTR combination control by numerical simulation. Results reveal that the adaptive filter and LQG/LTR compensator combination control is more effective and has less tracking residual error.
Optimization of yoke of a large telescope for mechanical reliability
Kai He, Wenli Ma, Jinlong Huang
In the large telescope using hydrostatic bearings, what will happen if the deformation of supporting pad and sliding surface exceed expectation? Obviously, mechanical reliability of the telescope will be bad. In order to decrease this deformation of a large telescope, yoke of the telescope was optimized. The principle and process of this work and Finite Element Analysis (FEA) are introduced in detail. According to the FEA result, the deformation of supporting pad decreases 32% and sliding’s decreases 36.7% after optimizing. The result shows that this work is effective to decrease the deformation of the two important surface and helpful to promote mechanical reliability of the telescope.
Optical design of Cassegrain system with wide field of view for spaceborne remote sensing application
Xiaoyan Yang, Anbing Geng
The paper presents an efficient approach to design a Cassegrain optical system for spaceborne remote sensing. The optical system has a focal length of 1000mm, F number of 5.6, the range of spectral band 0.4~0.9μm, and field of view 3°, distortion smaller than 1%. The effect of central obscuration on the image quality in the optical reflective system design is analyzed. It provides proof for reasonable choose of obscuration ratio in optical system design. With the help of CODE V software, the final two designs are obtained by a simple and quick optimization step, the image quality of which reaches the diffraction limit. It is shown the second structure style is designed by making the surface of primary mirror in the Cassegrain system hyperbolic, adding two high order aspheric surfaces and removing two lenses from lens compensator, and therefore the second with the simpler structure, smaller size and lighter weight, comparing with the first structure style, can be used in spaceborne remote sensing.
Design and analysis of structure of large aperture three-mirror off-axis optical system
Ke-jun Wang, Ji-hong Dong, Wei Li, et al.
On the basis of characteristics of optical system of Large aperture three-mirror off-axis, the mirrors’ support structure and the overall frame structure of the optical system was designed and investigated, the first and foremost is the lightweight of the support structure and the overall frame structure, the structure design of the three-mirror off-axis optical system was completed, which characteristic is integrative design of the overall frame structure , also the 3D model of the structure of the optical system was built, by means of the finite element analysis techniques, the modal analysis was done to the overall structure, the analysis results indicate that the first natural frequency of the overall structure is 162Hz,which is higher than 120 Hz requested by the overall structure of the optical system ,the overall structure have a high enough dynamic stiffness and reasonable distribution of modal, which ensure the overall structure in transportation and launch process to withstand severe vibration condition, and the shape error variation RMS and PV of optical mirror which are important indexes of image quality under the comprehensive influence of gravity and thermal load which is in the control range meet the design index.
Design and analysis on a kind of primary reflector support structure based on thermal compensation principle
Conglin Yan, Weilin Liu, Qinzhang Wu
While the diameter of primary mirror becomes lager and lager, the accuracy of surface shape becomes extremely sensitive to gravity and temperature. The support structure has great significance to improve the imaging quality. The accuracy of surface shape can be improved by increasing the stiffness of support structure. However, high stiffness will decrease the structure's thermal stability. To improve the imaging quality under thermal environment, the structure should have reasonable flexibility. The problem is that, the support structure of a primary mirror can't keep both high rigidity and fine thermal stability. To solve this problem, a flexible and thermal compensation structure was introduced and the parameter was optimized in this paper. After the analysis of the surface accuracy by Finite Element Method (FEM) was carried out, the RMS value of surface precision decreased from the original 67.3nm to 12.6nm when the mirror working at thermal and self-gravity circumstance. The analysis results meet the requirement of the imaging quality. It indicates that thermal compensation structure can effectively improve the reflector's surface shape accuracy under the effect of the gravity and thermal load.
Thermal analysis of a 1.8m solar telescope mechanical structure
Cheng Li, Hao Xian, Jun Zhang
According to the thermal environment of a 1.8m open structure solar telescope, a passive thermal control scheme of the mechanical structures is designed to reduce the effects of air turbulence and thermal deformation in this paper. Geometric characteristic of the open structure and the coating properties of mechanical structure are discussed. The stringent thermal requirements for the telescope mechanical structure should be satisfied to avoid the thermal inhomogeneity of ambient air at an intolerable level. A detailed finite element model with environmental conditions is presented to analyze the thermal response of the telescope mechanical structure. Thermal deformation and stress are also studied with the same finite element model. The numerical results demonstrate that the approach of passive cooling is effective and feasible.
Applications of liquid crystal adaptive optics for larger aperture telescope
Zhao-liang Cao, Li Xuan, Quan-quan Mu, et al.
In this paper, the advances in liquid crystal adaptive optics system (LC AOS) are presented for Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CIOMP, CAS). The LC AOS has two bottlenecks of low energy utilization ratio and slow correction frequency. To solve these problems, a series of effective methods were utilized by the LC AOS working group. The problem of energy utilization ratio was solved and the energy utilization ratio was improved from 5% to 85%, which was similar to the deformable mirror based AOSs. Furthermore, the correction frequency of the LC AOS was also greatly improved from 5Hz to 140Hz, which is closed to the ability of correction the atmospheric turbulence. According to these research results, two LC AOSs, which correspond to a 2.16 meter Telescope (located at Xinglong Station of Beijing Astronomical Observatory) and a 1.2 meter telescope (located at CIOMP, CAS), were designed and fabricated. By using these LC AOSs, the star was observed with adaptive correction and the correction is effective. At last, the resolution ability of the star is up to 1.7 times of the diffraction limitation for the 1.2 meter telescope.
1-m lightweight mirror design using genetic algorithm
Hagyong Kihm, Il Kweon Moon, Ho-Soon Yang, et al.
We present our design procedure for a 1-m lightweight mirror in a space optical system. The glass mirror has three monolithic bosses at the rim and is assembled with metallic bipod flexures. Their dimensional parameters cannot be optimized independently with each other in a classical design process, where optical performance is greatly affected by the flexure mount configuration. With our method, the design problem is separated into two independent problems; mirror design and flexure design. Resources required to achieve design goals are reduced by almost one order of magnitude in time. Also the mirror and flexure mount designs can be parallel-processed without interfering each other. In this paper, we present the mirror design process and its results optimized with multi-objective genetic algorithm (GA).
Study on numerical simulation of the dynamic impact effect for optical glass grinding with single grit
Jiang Chen, Feihu Zhang, Zhao Hang, et al.
It studies failure mechanism of optical glass with impact stress from grit, according to the dynamic impact effect in the process of optical glass grinding with single grit. With the distribution regularity of crack which from the grit dynamic impact, it established mathematical model of cylindrical stress wave which coaxial with wavefront. Analyzing and establishing the control equations for cylindrical stress wave, using finite-difference technique to simulate the dynamic impact effect for optical glass grinding with single grit and adopting Zwas numerical methods with source term hyperbolic curve partial differential equations to analysis and study the dissemination rule, diffusion rule and change rule, the simulation analysis shows that in the dissemination process of grit impact wave , wavefront occurred diffusion and there are tensile stress generated as well as oscillation.
A novel method for calibrating the image distortion of the interferometer
Fengtao Yan, Bin Fan, Xi Hou, et al.
Based on the distortion theory of the image system and interferometer theory, the distortion of interferometer system is analyzed, and a novel calibration and correction method for the imaging distortion is proposed. Two different subapertures are gotten by the interferometer, which have the common area of the test surface. The image distortion coefficients of the interferometer system are gained through the relationship of the two different subapertures, and we use the optical distortion coefficients to reconstruct the phase map that correspond to the real distribution.
Coating the 2-m level primary mirror with protected aluminum
Wenjun Pei, Hongxiang Liu, Weichuan Du
In order to evaporate the Ø 2.4m large-scale speculum, we have developed a high-vacuum resistance evaporation machine which is of the nation’s largest bell-type, and we first propose to use the structure of the protected-Al coating with SiO coating by evaporating from top to bottom. The results show that the non-uniformity of aluminum coating is no more than 5.17% within 1.8 meters in diameter, also after environmental testing, there is no change on the mirror surface, and the reflectance decreased less than 1%. The average of the speculum reflectivity is Rav<88%@350nm-1800nm and Rav<90%@ 400nm-2500nm.We have separately completed the Ø 1.8m plane mirror in April 2011 and the Ø 1.8m concave mirror in October 2011. The results show that the PV value is less than λ/10 after evaporation and the RMS value has no change.
Hyperspectral target detection based on improved automatic morphological endmember extraction method
Xu-guang Sun, Jing-ju Cai, Zhi-yong Xu, et al.
At present, commonly endmember extraction of hyperspectral is mainly concentrated in the spectral region. Because the spatial information is not used enough, the endmember extraction is not precise which can lead to a bad result of mixed pixel decomposition and hyperspectral target detection. Actually, the distribution of endmembers in space has a certain shape and aggregation. By making use of these information we can extract more precise endmembers. Automatic morphological endmember extraction technology can make full use of abundant spectral information and spatial information. This paper based on the existed automatic morphological algorithm, presents a method in combination with maximum distance for morphological endmember extraction to solve the influence of spectral variations, which effectively extracts different classes of endmember curves. Based on the theory of orthogonal subspace projection, the authors propose an improved constrained energy minimization (CEM) algorithm, achieve better hyperspectral target detection results.
Study of gray image pseudo-color processing algorithms
Jinlong Hu, Xianrong Peng, Zhiyong Xu
In gray images which contain abundant information, if the differences between adjacent pixels’ intensity are small, the required information can not be extracted by humans, since humans are more sensitive to color images than gray images. If gray images are transformed to pseudo-color images, the details of images will be more explicit, and the target will be recognized more easily. There are two methods (in frequency field and in spatial field) to realize pseudo-color enhancement of gray images. The first method is mainly the filtering in frequency field, and the second is the equal density pseudo-color coding methods which mainly include density segmentation coding, function transformation and complementary pseudo-color coding. Moreover, there are many other methods to realize pseudo-color enhancement, such as pixel’s self-transformation based on RGB tri-primary, pseudo-color coding from phase-modulated image based on RGB color model, pseudo-color coding of high gray-resolution image, et al. However, above methods are tailored to a particular situation and transformations are based on RGB color space. In order to improve the visual effect, the method based on RGB color space and pixels’ self-transformation is improved in this paper, which is based on HIS color space. Compared with other methods, some gray images with ordinary formats can be processed, and many gray images can be transformed to pseudo-color images with 24 bits. The experiment shows that the processed image has abundant levels, which is consistent with human’s perception.
Fabrication of 1.8m standard spherical mirror
Jun Yu, Shidong Shen, Junhe Pan, et al.
Ritchey-Common test of the large flatness is an effective method, which requires a larger aperture standard spherical mirror. It’s very difficult for manufacture of large-aperture spherical mirror in the area of optical fabrication. The producing technology of the large-aperture standard spherical mirror with aperture of 1.8m is mainly stated in this paper. The solutions to solve the problems during manufacture are discussed, and the attentions during production are concluded. To offset the gravity effect and ensure the surface deformation satisfy the design requirements, the mechanic support structure including hammer and floating support of spherical mirror are illustrated in brief. At last, the analysis and data of measurement given by 4D interferometer satisfy the technical indicators.
Analysis of deforming a 1.5-m ultrathin spherical mirror into an off-axis parabola
Chunmei Zeng, Jingchi Yu, Peiji Guo
The collimating mirror is a key component of a solar simulator. It is generally made up of one large spherical or aspherical mirror or some small unit mirrors. By using active optical technology, a spherical mirror can be deformed into an off-axis parabola. This paper reports a finite element analysis process with a 1.5-m ultra-thin spherical mirror. The best fitting spherical surface, active control method, actuator arrangements are introduced respectively. The analysis results show that the surface quality(=2.258 μm RMS) with an arrangement of 21 actuators meets the accuracy requirement, and the maximum stress(=0.979MPa) is less than allowable stress(=3.43 MPa). Finally, 1.5-m prototype mirror and its active support structure are presented. This method is effective for non-imaging optical systems with low precision.
Optical testing of & #934;340mm F/1.3 aspheric surface
Jianfeng Ren, Peiji Guo
Two different optical testing methods which used to test aspheric surface are introduced in this paper. An aspheric surface of Φ340mm F/1.3 is tested with help of Computer-generated hologram (CGH) or Null compensator, and then these two testing results are compared. Matched result proves that these methods are believable and reliable. This compare testing method can be introduced to test similar aspheric surface.
Research on reflective optical telescope system's wavefront aberration compensation method
Xueting Duan
Wavefront aberration measurement of the image quality of reflective telescope system which has a large aperture and long focal length is one of the frequently–used methods of high-precision test and alignment. It was widely used during the large aperture telescope manufacturing process. The influences of surface shape error of the reflective optical telescope system components were simulated and analyst by input the actual measuring data into the optical design software CODE V in this article. According to the test results compared to the alignment process, the accuracy of the simulation method was indicated. At the same time, the wavefront aberration optical compensation principle of the reflective optical telescope system was proved by the simulation of alignment. And in this article, the feasibility of the application of optical phase compensation alignment method was investigated.
Theoretical and experimental study on the active support for thin mirror
Yongqian Wu, Yudong Zhang, Fan Wu
The model of the active support is established. The related deforming theories and methods of controlling are described. The experiment of active system of 31 units, Φ300mm demonstrates the validation of the control algorithm. The whole system has the convergence efficiency of 96% of the surface.
Optical design of satellite laser communication integrative transceiver
Yanyan Cheng, Xuewu Fan, Gangyi Zou, et al.
According to technical requirements of satellite optical communication, a set of optical system of transmitter and receiver with a common optical antenna is designed at 850nm. We select a Cassegrain-type afocal off-axis system as the optical antenna structure. The entrance pupil diameter is 150 mm. The field of view of transmitter and receiver is ±100μrad and ±5mrad, respectively. This optical system has a simple and feasible configuration. The design results show that system performances are acceptable. The MTF is close to the diffraction limit. The energy concentration ratios are more than 90% at 30μm of diameter of circle. The RMS of wave front aberration is less than λ/20.
Study on large aperture SiC mirror technology
In order to develop space or ground large optics system, the technology study of large aperture SiC mirror were studied in detail. In this article the optimization of new mirror materials was introduced, the fabrication technologies of SiC mirror were studied, and the application of SiC mirrors was elaborated. At the same time, the SiC mirror technology and directions in china were expressed.