Large-aperture Optical Elements Research Articles

Error analysis of precision scanning system for measuring reflectivity of large-aperture optical elements

为测量高能激光传输系统中大口径高反射率光学元件的反射率，设计了一种大口径光学元件二维扫描的精密测量系统。介绍了该系统的结构及其工作原理，分析了影响系统测量精度的因素，从理论上分析了扫描系统的系统误差对测量精度的影响，结果表明在垂直于光束传播方向上，水平偏差在0.29 mm时，测量误差在10⁻⁶量级；腔长的变化量较小时，可通过对衰荡腔腔镜的调节,实现对旋转轴偏差的补偿及对系统的精细调节。通过拟合处理光强与时间的数据得到对应的一次指数函数拟合曲线，并通过计算得到衰荡时间和反射率，经过对比分析可知，该误差分析方法能比较有效地测量腔镜的反射率,并能减小实验数据本身带来的误差。

Stress and wavefront measurement of large-aperture optical components with a ptychographical iterative engine.

The clamping stress of large-aperture optical elements has a significant influence on the optical quality of the system. In this study, a comprehensive measurement system combined with ptychographical iterative engine (PIE) wavefront sensors and polarization components is developed to determine the stress distribution of the optical elements and its effect on the transmitted and reflected wavefronts. This system avoids the use of multiple measuring instruments and has low cost and strong anti-interference ability. The experimental results demonstrate that the stress distributions measured at different resolutions are consistent with the finite element analysis, and the wavefront measurement accuracy is 0.1λ. This test configuration is very flexible and provides a useful means for online installation and quality control of large-aperture optical systems.

Equipment for in situ measurement of machining defects of large aperture optical elements

AbstractA set of in situ measurement equipment of large aperture strong light element based on the principle of laser scattering is established. The size and distribution of defects (damage points) can be judged by the laser scattering signal. The maximum scanning range is 700 mm*1000 mm. The type and size of defects are directly obtained by scanning the quartz sample with a diameter of 100 mm. The types of defects are pitting and scratches, and the width of the scratches and the diameter of the pitting are mostly in the range of 0–10μm. The processing time could reach 31.06s. The device can realize the on‐line in situ measurement of large aperture optical elements, and has the advantages of fast response speed and high measurement accuracy.

Method to improve the surface shape of BK7 glass in full-aperture polishing.

Full aperture polishing is a significant process to fabricate optical workpieces with nano figure precision. It has the characteristics of excellent full spectrum uniform removal ability, fast convergence speed, high machining accuracy, and low production cost, which makes it the first choice for the processing of large-aperture optical elements. However, with BK7 glass it is difficult to achieve deterministic processing due to its large thermal expansion coefficient and other factors, and the surface shape accuracy is difficult to improve. In this paper, the thermal deformation of BK7 glass is analyzed first, and then the temperature distribution in the element is measured during full-aperture polishing. The influence of the temperature field in the optics on the accuracy of the final surface shape is analyzed, and the quantitative relationship between the temperature difference and the surface shape is established. In addition, the methods of deterministically controlling the surface shape of optics such as polishing liquid temperature control and immersion polishing are proposed. Finally, the model of quantitative control of the surface shape of optics is verified by experiments, which improve the surface shape accuracy of 600 mm BK7 optics to 0.2λ.

Phase defect detection of large-aperture optics with static multiplanar coherent diffraction imaging.

Phase defect detection with micrometer scale on large aperture optical elements is one of the challenges in precision optical systems. An efficient scheme is proposed to detect phase defects. First, the defects are positioned in a large aperture by dark-field imaging based on large aperture photon sieves to improve the detection efficiency with a relatively low cost. Second, static multiplanar coherent diffraction imaging is used to retrieve the phase of the positioned defects in a small field of view. Here, a spatial light modulator is used as a multifocal negative lens to eliminate the mechanical errors in multiplanar imaging. The use of a negative lens instead of a positive lens has the advantage of a larger imaging space for the system configuration. Compared to the traditional interferometry system, this diffraction detection system has a simpler optical path and doesn't require sparse distribution of the defects. Experiment results demonstrate the success of the proposed scheme with a detection resolution better than 50 µm. We believe this work provides an effective method to rapidly detect phase defects on large aperture optics with high accuracy and high resolution.

Dwelling time calculation for film uniformity correction by ion beam sputtering process on larger optical materials

It is difficult to obtain film with uniform thickness and constant performance for optical components with larger diameter. It is a critical technology to improve the film uniformity during the deposition process. The ion beam sputtering system was used to prepare the film on the surface of large-aperture optical elements. The performance of film including thickness and roughness were measured by step profiler and optical profilometer instrument. The film thickness correction model was proposed in this paper. The optimized dwell time ratio was obtained by the film thickness data obtained from former experiments, and the dwell time distribution was calculated, after several iteration with the model, uniform film can be achieved on optical elements over 300mm in diameter. Taking the Si film on the surface of fused silica as an example. The research results show that, different film thickness between 100nm and 400nm can be obtained, when the film thickness is more than 200 nm, the film uniformity from more than 13% to less than 0.5%. The surface roughness variation of optical material before and after film deposition were studied, which provide stable process for obtaining high performance film on larger optical components.

An Intelligent Manufacturing Solution for High Precision Large Aperture Light-Weighted Optical Mirrors

In order to meet the requirements of high precision and deterministic manufacturing of large mirrors in aerospace fields, a workshop solution for intelligent production of large aperture and light-weighted optical elements is proposed, combining modern optical manufacturing technology, network technology, sensing technology and some other technologies. This solution mainly involves five systems, such as workshop production management system, virtual workshop system, workshop object sensing system and so on. It can theoretically improve controllability of the manufacturing process and the quality of conducts.

大口径光学元件功率谱密度的拼接干涉检测

大口径光学元件功率谱密度的拼接干涉检测

In situ detection and evaluation of surface defects for large-aperture optical elements

In situ detection and evaluation of surface defects for large-aperture optical elements

基于离子束溅射大口径光学元件平坦化层均匀性研究

基于离子束溅射大口径光学元件平坦化层均匀性研究

Modelling and simulation of mid-spatial-frequency error generation in CCOS

BackgroundThe computer-controlled optical surfacing (CCOS) technology, which has advantages of high certainty and high convergence rate for surface error correction, has been widely applied in the manufacture of large-aperture optical elements. However, due to the convolution effect, the mid-spatial-frequency (MSF) errors are difficult to be restrained in CCOS.MethodsConsequently, this paper presents a theoretical and experimental investigation on the generation of MSF errors, aiming to reveal its main influencing factors, and figure out the optimized parameters and the controlling strategies for restraining MSF errors. A surface topography simulation model for the generation of MSF errors was established first. Based on which, orthogonal simulation experiments were designed and conducted for the following three parameters, i.e., tool influence function (TIF), path type, and path spacing. Subsequently, the proposed model was verified through the practical polishing experiments.Results and conclusionsThe results demonstrated the influencing degree of the parameters and the optimized combination of parameters, and provided process guidance for restraining MSF errors in CCOS.

Instantaneous wavefront measurement of large aperture optical elements

In order to measure the instantaneous wavefront of large aperture optical elements, a method based on the structure of oblique incidence of reflective shearing point diffraction interferometer is proposed. A lateral displacement between the reference wavefront and the test wavefront is formed after passing this structure. The shear of two beams introduces linear spatial carrier frequency to the point diffraction interferogram. After receiving a good contrast interferogram, wavefront phase is retrieved by Fourier transform (FT) automatically to realize the dynamic measurement of instantaneous wavefront. The optical path is up to 20 m, so the air current is a significance factor to the result. Besides, because of the air current, the system itself can be seen as a instantaneous wavefront happening and measurement of large aperture optical elements. The results indicate that the root mean square value is in accord with that acquired by SID4 wavefront sensor (less than 1/50λ), so about the repeated accuracy. The method proposed can be applied in high resolution and accuracy measurement of instantaneous wavefront.

A Novel and Effective Surface Flaw Inspection Instrument for Large-Aperture Optical Elements

Surface defects on precision optical elements must be carefully inspected since they impact the normal operation of an optical system. It is a challenge to inspect defects of large-aperture optical elements using an imaging system because of efficiency and accuracy. This paper designs a novel and effective inspection instrument with two imaging systems for large-aperture optical elements. They are the dark-field imaging system (DFIS) with a line scan camera in 10-μm resolution and the bright-field (BF) imaging system with a microscopic camera in a 0.85-μm resolution. To keep the clarity of the DFIS in large-scope quickly scanning, an adaptive scan path planning method is proposed. A set of novel algorithms is proposed to process a large number of dark-field images. Due to the limitations of the DFIS in scattering effect, the corresponding BF images are obtained according to the dark-field images. The classification of flaws and their sizes measurement based on BF images are also presented. The experiments show that the instrument can scan an optical element with the size of 810 mm × 460 mm in less than 6 min and the inspection precision can reach 3 μm.

Belt-MRF for large aperture mirrors.

With high-determinacy and no subsurface damage, Magnetorheological Finishing (MRF) has become an important tool in fabricating high-precision optics. But for large mirrors, the application of MRF is restricted by its small removal function and low material removal rate. In order to improve the material removal rate, shorten the processing cycle, we proposed a new MRF concept, named Belt-MRF to expand the application of MRF to large mirrors and made a prototype with a large remove function, using a belt instead of a very large polishing wheel to expand the polishing length. A series of experimental results on Silicon carbide (SiC) and BK 7 specimens and fabrication simulation verified that the Belt-MRF has high material removal rates, stable removal function and high convergence efficiency which makes it a promising technology for processing large aperture optical elements.

The Large Aperture Optical Elements patent search system based on Domain Knowledge Organization System

Effective use of patent information provides a multiplier effect in product design and new technology development. This paper reports research on using an open-source extraction tool—General architecture for text engineering (GATE) and word split software—from the Institute of Computing Technology and Chinese lexical analysis system (ICTCLAS) to assist the expert in acquiring and marking of feature word groups from the abstracts and claims of the patents on Large Aperture Optical Elements. Then, it used the experts feature word groups, which were formalized by INSPEC control words, to construct a Domain Knowledge Organization System (DKOS). Base on the DKOS, a retrieval module of patent information is constructed, which has practical significance for designers to design products and develop new technology. The system is a visual application system, for example, which can filter patent documents by topics and retrieve relevant topics via sample text.

Design and machining of Fresnel solar concentrator surfaces

Fresnel lens is found to simplify the system structure and enhance the performance of photovoltaic systems. The flat and arched shape Fresnel lens surfaces are designed, respectively, based on 2D geometric construction method (GCM) in this paper. The slope facets of Fresnel lens are simplified as points, which control the light accurately. This theory is applied for large aperture optical elements to realise light and thin design. The designed concentrator surfaces are fabricated by ultra-precision turning technology. The performance of Fresnel concentrator is checked by testing the efficiency of solar cell, and the experimental results prove that the proposed design method of Fresnel concentrator surfaces meets the application requirements on photovoltaic system.

Research on Stitching Algorithm of Large Aperture Optical Elements Piecewise Measurement Data

Due to the range of the measuring system is limited in the measurement of large aspheric optical elements, test is hard to be once fulfilled, so coordinate measurement based on multi-section stitching is proposed, and the least square mathematical model of large aperture optical elements multi-section stitching is built. Moreover, the profiler Talysurf PGI 1240 made by Taylor Hobson company is used for study. The result shows that, the method is suitable for multi-section data stitching for large aspheric optical elements, and possesses many advantages, such as fast speed, high accuracy and strong operability, etc.

大口径光学元件磁流变抛光工艺软件设计

大口径光学元件磁流变抛光工艺软件设计