Large-aperture Mirror Research Articles

Tool mark prediction on the surface of large-aperture mirrors via magnetorheological finishing.

The magnetorheological finishing (MRF) of surfaces often results in tool mark errors. A prediction model can effectively guide subsequent processing, necessitating thorough research. To address this issue, this paper introduces an enhanced continuous tool influence function method. This method involves sub dwell time convolution with varying tool influence functions, enabling tool mark prediction. Numerical simulations demonstrate the proposed method's effectiveness, while the data size is estimated to confirm its economic properties. Subsequently, a MRF experiment was conducted, affirming the practicability through power spectral density evaluation. A fast algorithm is given to guide tool mark predictions on large-aperture mirrors fabrication engineering subjected to sub-aperture polishing.

Surface Analysis and Optimization of Large Aperture Mirror Supported by Elastic Expansion Sleeves

In order to meet the stability of the support structure of arrayed large aperture mirror and improve the surface accuracy of the mirror, the elastic expansion sleeve is proposed as the back-support structure of the large aperture mirror. The feasibility of the support method is verified by theoretical analysis and experiment. The PV value of additional wavefront distortion is about 75.3nm<λ/5(λ=632.8nm) when the torque of single mandrel screw is 40N·cm, which meets the technical specifications. The change trend of the support-induced surface is compared between the finite element simulation and the measured results under different mandrel screw torque conditions. When the support torque is increased in equal increments, there is a linear positive correlation between the PV value of support-induced surface and the support torque. Based on the change trend of the support-induced surface, the optimization design scheme of the initial surface is proposed. And the simulation results show that the optimized induced distortion is smaller than that of the ideal surface (the compensation ratio is 7.68%), which reduces the additional wavefront distortion under the actual mounting support.

Adjustment and testing method of large aperture mirror Bipod support structure

Adjustment and testing method of large aperture mirror Bipod support structure

The six-degrees-of-freedom attitude measurement instrument for the large aperture mirror using the prepressing sensors and flexible supporting.

To achieve precise measurement of a large aperture mirror, a six-degrees-of-freedom (6-DOF) measurement instrument is designed to monitor and calculate the real-time attitude of the mirror. Magnetoelectric displacement sensors are prepressed, and a flexible sensor supporting is designed to achieve high-accuracy measurement. The relationship between 6-DOF displacements of the mirror and the six sensor values can be obtained using the coordinate system transformation and Jacobian matrix. The Newton's iteration method is used to decouple the strong coupling measurement system, and 6-DOF displacements are obtained. The displacements directly measured by using laser sensors are compared with the calculated values in the experiments, the minimum average error of the measured displacement is 1.87%, and the mean difference of the displacement is 0.43 µm.

Analysis and experiment of a pneumatic-hydraulic composite support system for in-situ mirror processing and testing.

To address the deformation issues caused by the self-gravity and machining stresses in the process of large-aperture mirror fabrication, this paper proposes an in-situ switchable pneumatic-hydraulic hybrid supporting system that enables the seamless transition between machining and testing. By facilitating in-situ switching, this system not only reduces the machining time of large-aperture mirrors, thereby enhancing production efficiency, but also mitigates the risks associated with traditional switching methods that may result in mirror damage due to human error. Three typical working conditions of the hybrid supporting system, namely hydraulic machining support, air-floating testing support, and three-point rigid support, are investigated in terms of mirror loading through a finite element simulation. Additionally, an experimental platform is constructed to validate the proposed system. The experimental results affirm the feasibility of the designed pneumatic-hydraulic hybrid supporting system. This system will serve as a technological support to advance the rapid development of large-aperture space telescope manufacturing techniques.

A Pointwise-Optimal Ensemble of Surrogate Models

AbstractThe ensemble of surrogate models is commonly used to replace computationally expensive simulations due to their superior prediction accuracy and robustness compared to individual models. This paper proposes a new pointwise ensemble of surrogate models, namely, a pointwise-optimal ensemble of surrogate models (POEMs). To address the limitations of the cross-validation (CV) error in evaluating the performance of regression surrogate models, this paper introduces the compensated cross-validation error, which is more reliable in selecting better individual surrogate models and improving the accuracy of surrogate model ensembles. To overcome the limitations of CV error in calculating pointwise weight factors, this paper designs and solves an optimization problem at training points to obtain corresponding pointwise weight factors. Additionally, this paper proposes two weight calculation methods to be applied in the interpolation and extrapolation regions, respectively, to reduce the instability of ensembles caused by extrapolation. Thirty test functions are employed to investigate the appropriate hyperparameters of POEM and the Friedman test is used to verify the rationality of the α value. The thirty test functions are also used to examine the performance of POEM and compare it with state-of-the-art ensemble surrogate models. Furthermore, POEM is applied to a large-aperture mirror holder optimization case to verify its superiority. The results demonstrate that POEM presents better accuracy and robustness than individual surrogates and other compared ensembles of surrogate models.

Post Optical Freeform Compensation Technique for Machining Errors of Large-Aperture Primary Mirror

Large-aperture space optical systems are important tools for observing our planet and conducting deep-space scientific research. More requirements have been put forward for large-aperture optical systems as the depth and breadth of related applications continue to increase. However, achieving the desired surface accuracy on lightweight materials for large-aperture mirror brings higher demands on relevant processing technologies, which increases the processing difficulty, cycle, and cost of large-aperture optical systems. Therefore, it is necessary to develop a new optical system technique with high tolerance for primary mirror machining errors to significantly reduce its machining accuracy requirements. This paper proposes a new optical system technique which introduces a small-aperture free-form surface into the large-aperture optical system’s post optical path. By combining the freeform correction and its misalignment on the system’s aberrations, the system’s wavefront can be adjusted to correct the wavefront distortion caused by the primary mirror’s machining errors. This reduced the machining accuracy requirements of the large-aperture primary mirror by about one order of magnitude, and high-quality imaging with a low-precision primary mirror is achieved.

A Review of Lightweight Design for Space Mirror Core Structure: Tradition and Future

With the continuous improvement of the imaging quality requirement of the space optical system, the large-aperture mirror becomes the research focus. However, the increase of the aperture will increase the whole weight which results in high launch cost and degrades the mirror surface figure accuracy. Therefore, the lightweight design method of the mirror structure is of great importance. In recent years, many space telescope system schemes have demonstrated the progress of the structural lightweight design of mirrors, such as Spitzer, SOFIA, JWST, etc. This article reviews the main content and innovations of the research on the structural designs of mirrors including conventional machining designs and topology optimization structures. Meanwhile, some emerging designs (e.g., lattices and Voronoi structures) considering additive manufacturing (AM) are also introduced. Several key elements of different structural design approaches for lightweight mirrors are discussed and compared, such as material, lightweight ratio, design methods, surface figure, etc. Finally, future challenges, trends, and prospects of lightweight design for mirrors are discussed. This article provides a reference for further related research and engineering applications.

Microstress bonding design of low-distortion mirror assembly

To address the problem that bonding can lead to a reduction in the surface shape precision of a space-bound mirror, relationships between mirror deformation, thermal stress, and curing shrinkage stress were studied, and a bonding microstress design route was proposed. The thermal stress and thermal deformation introduced by thermal expansion mismatch were eliminated through an athermal adhesive layer thickness design. The relationship between mirror deformation and the curing shrinkage of the adhesive layer was derived completely, and structural optimization measures for releasing the curing stress of the adhesive layer are given. Bonding stress analysis was conducted based on the equivalent thermal deformation method, and an optimal structure meeting the design requirements was obtained. Finally, bonding of the mirror assembly was completed via this route, and the measured surface shape precision was stable at 0.0225λ. The theoretical analysis and experimental study demonstrate that this bonding design method can predict the bonding stress in the assembly process, making the follow-up bonding result controllable. These results should provide an excellent reference for the design and high-precision integration of large-aperture mirrors.

High speed surface defects detection of mirrors based on ultrafast single-pixel imaging.

High speed surface defects detection of mirrors is of great significance, for detecting the quality of the mirrors on-site, and ultimately for monitoring the operating states of laser systems. The speeds of conventional proposals are relatively low as they utilize mechanically scanning methods or two-dimensional charge-coupled devices. Here, we propose a high speed surface detection method based on ultrafast single-pixel imaging, which consists of a spatial Fourier optical module for frequency-space mapping and a dispersive Fourier transform module for frequency-time mapping. An optical grating is utilized to map the wideband spectrum of dissipative soliton into the spatial domain under far-field diffraction, where the mirror is inspected. Dispersive Fourier transform is used to map the surface-defects-coded spectral information into the temporal domain, then recorded by a high speed single-pixel detector. The detection system permits continuous single-shot spectra measurement with a frame rate equivalent to the pulse repetition rate (8.4 MHz). We extract amplitude defects by demodulating light intensity, and obtain phase defects by demodulating the interference spectrum with a Mach-Zehnder interferometer structure. Experimental results show that the damaged mirror with a two-dimensional width of 10 × 13 mm can be obtained with a spatial resolution of 90 µm. The obtained phase accuracy after Hilbert transformation is 0.00217 rad, corresponding to a depth resolution of 51 nm. This scheme can find promising applications for surface defects detection of large aperture mirrors, and real-time monitoring of laser systems with high energy.

0 g surface figure test of large aperture mirror supported by Bipod

0 g surface figure test of large aperture mirror supported by Bipod

Design of online damage images detection system for large-aperture mirrors of high power laser facility based on wavefront coding technology

The laser transport system of the high power laser facility is mainly composed of large-aperture laser transport mirrors (TMs). Obtaining the high-resolution online damage images during the operation, which is of great significance for operating safely of the mirrors and the facility. Based on wavefront coding, pan-tilt scanning and image stitching technologies, an online laser-damage images detection system is designed, and it can achieve high-precision detection of surface characteristics of large-aperture laser transport mirrors. The preliminary simulation proves that the system can solve the depth of field matching problem caused by pan-tilt tilt imaging and achieve higher resolution.

Optimization of Thickness Uniformity Distribution on a Large-Aperture Concave Reflective Mirror and Shadow Mask Design in a Planetary Rotation System

Improving the spatial resolution of remote sensing satellites has long been a challenge in the field of optical designing. Although the use of large-aperture reflective mirrors significantly improves the resolution of optical systems, controlling the film thickness uniformity remains an issue. The planetary rotation system (PRS) has received significant attention owing to the excellent uniformity of the coating applied to the large-aperture reflective mirror. However, the development of the PRS remains hindered by a lack of research on its properties and the design method of the shadow mask. To address this, we performed a theoretical analysis of the distribution of film thickness and uniformity in the PRS, which is impacted by parameters of geometric configuration in the vacuum chamber. We present a film thickness expression based on Knudsen’s law and the geometric configuration of the vacuum chamber that incorporates an additional shading function. Moreover, the variation of uniformity in the standard and counter PRSs was elucidated by changing the location of the evaporation source. Finally, a fixed-position shadow mask, which was obtained by theoretical design, allows the nonuniformity of the concave reflective mirror (with a 700 mm aperture) to reduce from 2.43% to 0.7%, highlighting the importance of initial shape design.

Large Aperture Mirror Surface Test

The large aperture mirror surface test is the basis of optical processing and alignment, and is also the key to the development of remote sensing device. The simulation results show that the RMS values of 1.07 m primary mirror with multi-point support and sling support are 1.86 nm and 3.28 nm respectively. Using 36 point unloading device, sponge 36 point free support and sling support to test the mirror surface, the results are basically consistent, RMS is better than 0.02λ (λ = 632.8 nm).

Research on high performance support technology of space-based large aperture mirror

A three-point back support structure including cone sleeve, flexible structure and adjustable pad is designed for the space-based mirror support to meet the requirements of small surface shape error, high supporting reliability and stability, of which in-depth study on support principle and engineering realization is conducted in this paper. The error sources which influence the surface shape error of the mirror subassembly with three-point back support is summarized. The mechanism of surface shape variation caused by various error sources is studied. The support structure with high stiffness for alleviating the surface shape error caused by various error sources is designed, which can increase the fundamental frequency of mirror subassembly and protect it from yield failure under the condition of dynamic load. Firstly, the static and dynamic simulation of the three-point back support structure model is carried out by means of finite element analysis. Then the dynamic and partial static experiments are performed using aluminum mirror and actual supporting structure. The results show that the surface shape error of mirror with the three-point support structure is superior to λ/80(λ = 632.8 nm), the displacement of mirror is smaller than 0.015 mm, the inclination angle is smaller than 2″, the mass of the mirror subassembly is smaller than 310 kg. The mirror subassembly has a reasonable modal distribution, the fundamental frequency is 128 Hz, which is much higher than the requirement of 120 Hz. The maximum magnification of the mirror assembly excited by the sinusoidal vibration and the random vibration is 2.51and the maximum stress is 286 MPa under the same working condition, which is much lower than the yield limit of the selected material. A kind of segmented metering assembly method is formed and applied to make sure 2 m space-based large-aperture mirror has lower surface shape error according to the theoretical research results in this paper which the surface shape error of the space-based large-aperture mirror supported by three-point on the back which optical axis is in the horizontal direction in test, installation and adjustment is very sensitive to the deviation between rotating shaft of flexible structure and the neutral plane of the mirror in the direction of the optical axis.

Overview of advanced manufacturing technology of large-aperture aspheric mirror

The aspheric surface can correct the system aberration and improve the image quality in the optical imaging system, in addition to that it can simplify the system structure significantly; On the other hand, the resolution of imaging system can be increased by improving the system aperture. Therefore, in the domain of basic scientific research, astronomical cosmological exploration and military defense security the large-aperture aspheric mirrors are all highly required. The manufacturing of large-aperture aspheric mirrors plays a critical role in modern optical engineering. This paper focuses on the advanced manufacturing techniques of large-aperture aspheric mirrors. The optical manufacturing technologies, especially the grinding and polishing techniques of large-aperture aspheric mirrors in the past half century and the surface shape testing methods during the grinding and polishing process, are reviewed. In particular, it summarizes the technical characteristics of advanced (new generation) optical manufacturing, and looks forward to the future manufacturing strategy of large-diameter aspheric mirrors.

Φ1.05 m轻量化反射镜设计与制造

针对Ф1.05 m空间光学系统主镜的设计指标要求，提出了轻量化反射镜结构优化设计的新方法，并建立了反射镜结构自动化仿真分析与优化设计平台，基于此平台确定了性能优异的主镜结构设计方案。主镜重量小于50 kg，轻量化率已接近国外先进水平；主镜在三球铰支撑下的第一阶模态频率为361.2 Hz，自由状态下的一阶非零模态频率为501.9 Hz；在1 ℃均匀温度变化下，不去离焦和去除离焦之后的面形RMS分别为0.55 nm和0.10 nm；主镜在30g过载加速度作用下的最大应力为16.1 MPa，均满足设计要求。采用目前最先进的第三代大口径反射镜加工工艺，路线为超精密铣磨—小磨头数控研抛—离子束精修，实现主镜面形误差的确定性去除。为保证面形检测结果的天地一致性，发展了重力卸载技术和面形误差数据后处理技术，剔除重力和其他系统误差对检测的影响。主镜最终面形精度达到0.011λ RMS，获得了高精度的光学面形，也证明了方案的合理性。

FPCB Masked One-Step Etching Large Aperture Mirror for LiDAR

This paper presents a Flexible Printed Circuit Board (FPCB) masked one-step etching large aperture mirror for Light Detection and Ranging (LiDAR). A FPCB structure is bonded on a thin silicon wafer ( $50\sim 200~\mu \text{m}$ thick) coated with a 100 nm thick metal film and one-step of DRIE is used to etch the wafer with the FPCB structure as the mask and the metal film as the stop layer. The simple fabrication process and 0.1 mm (instead of $ needed for microfabrication) resolution photolithography lead to a very low cost of a few dollars. Copper coils embedded in the FPCB structure are attached to the backside of the large aperture mirror plate, instead of beside the mirror plate as the case in MEMS magnetic mirrors, to generate a high magnetic force and achieve a relatively high frequency considering the large aperture and high thickness. Modeling and prototyping of two designs, Mirror_A and Mirror_B, are presented to verify the novel mirror technology. LiDAR applications of the novel mirror technology are demonstrated and tested. Achieved performances are: Mirror_A, aperture $12 \times 12$ mm, oscillation frequency of 510 Hz, field of view (FOV) of 30° and radius of curvature (ROC) of 10 m; Mirror_B aperture $24 \times 24$ mm, oscillation frequency of 160 Hz, FOV of 20° and ROC of 10 m. [2020-0085]

空间遥感相机大口径变方位反射镜设计

空间遥感相机大口径变方位反射镜设计

空间遥感相机大口径变方位反射镜设计

空间遥感相机大口径变方位反射镜设计