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Progress in the research of testing and evaluation techniques for spaceborne gravitational wave telescopes
Lanqiang Zhang, Yi Zeng, Xiaohu Wu, Jinsheng Yang, Xiaoli Ruan, Qiang Xin, Naiting Gu, and Changhui Rao
Spaceborne telescopes for gravitational wave detection crucially collimate bidirectional beams in ultra-long interferometric optical paths. The faint optical path changes due to gravitational waves demand pm-level optical path length stability and below 10?10 level backscattered light in the telescopes. The ultra-high-level specifications requirements are out of state-of-the-art testing techniques. The development of testing and evaluation techniques for spaceborne telescopes is a crucial prerequisite for the success of the space gravitational wave detection program. This paper overviews the development of spaceborne gravitational wave detection telescopes, focusing on the optical path length stability and backscattered light testing status, results, and further plans, providing reference in the testing and evaluation of Chinese spaceborne gravitational wave detection telescopes. Spaceborne telescopes for gravitational wave detection crucially collimate bidirectional beams in ultra-long interferometric optical paths. The faint optical path changes due to gravitational waves demand pm-level optical path length stability and below 10?10 level backscattered light in the telescopes. The ultra-high-level specifications requirements are out of state-of-the-art testing techniques. The development of testing and evaluation techniques for spaceborne telescopes is a crucial prerequisite for the success of the space gravitational wave detection program. This paper overviews the development of spaceborne gravitational wave detection telescopes, focusing on the optical path length stability and backscattered light testing status, results, and further plans, providing reference in the testing and evaluation of Chinese spaceborne gravitational wave detection telescopes.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 240027 (2024)
Special issue on telescopes for space gravitational wave detection (II)
Naiting Gu, Xiaoyong Wang, Desheng Wen, Changhui Rao, Zebing Zhou, and Xianji Ye
The detection of space gravitational waves is expected to reveal more mysteries of the universe. With the support of the National Key Research and Development Program of China, "Special issue on telescopes for space gravitational wave detection (II)" was organized by the journal Opto-Electronic Engineering. These papers in the special issue introduce the recent major research progress of the designs and analyses, construction and adjustable, and testing and evaluation of telescopes for space gravitational wave detection. They will provide a communication platform for the relevant field scholars and experts, and will actively promote the research process of the space gravitational wave detection project in China. The detection of space gravitational waves is expected to reveal more mysteries of the universe. With the support of the National Key Research and Development Program of China, "Special issue on telescopes for space gravitational wave detection (II)" was organized by the journal Opto-Electronic Engineering. These papers in the special issue introduce the recent major research progress of the designs and analyses, construction and adjustable, and testing and evaluation of telescopes for space gravitational wave detection. They will provide a communication platform for the relevant field scholars and experts, and will actively promote the research process of the space gravitational wave detection project in China.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 240026 (2024)
High-precision ground measurement technology research for measuring pointing deviation in space-based gravitational wave detection telescopes
Qilin Song, Yang Li, Ziye Zhou, Yawei Xiao, Jinsheng Yang, Linhai Huang, Naiting Gu, and Changhui Rao
The spaceborne telescope plays a critical role in detecting gravitational waves in space. Given transmission distances of approximately 109 meters between different constellations, there are stringent requirements for nanoradian precision in telescope pointing accuracy. Accurate pointing deviation measurement and calibration are essential prerequisites for achieving high-precision pointing in space-based gravitational wave detection telescopes. To meet the ground testing and sensor calibration needs for space telescopes' pointing deviation, this paper introduces a novel high-precision measurement method based on the Hartmann principle. By utilizing the concept of multi-aperture spatial reuse, this approach mitigates the impact of various sources of random errors, significantly improving the precision of pointing deviation measurements. The paper conducts an analysis and optimization of Hartmann sensor parameters, establishing a quantitative relationship between sensor parameters and pointing deviation measurement accuracy. The research findings demonstrate that the multi-aperture spatial reuse method based on the Hartmann principle can achieve highly precise measurements of telescope pointing deviations, with the accuracy as low as 0.32 nrad. This method offers a feasible approach and serves as a reference for ground testing and in-orbit sensor calibration of space-based gravitational wave detection telescopes. The spaceborne telescope plays a critical role in detecting gravitational waves in space. Given transmission distances of approximately 109 meters between different constellations, there are stringent requirements for nanoradian precision in telescope pointing accuracy. Accurate pointing deviation measurement and calibration are essential prerequisites for achieving high-precision pointing in space-based gravitational wave detection telescopes. To meet the ground testing and sensor calibration needs for space telescopes' pointing deviation, this paper introduces a novel high-precision measurement method based on the Hartmann principle. By utilizing the concept of multi-aperture spatial reuse, this approach mitigates the impact of various sources of random errors, significantly improving the precision of pointing deviation measurements. The paper conducts an analysis and optimization of Hartmann sensor parameters, establishing a quantitative relationship between sensor parameters and pointing deviation measurement accuracy. The research findings demonstrate that the multi-aperture spatial reuse method based on the Hartmann principle can achieve highly precise measurements of telescope pointing deviations, with the accuracy as low as 0.32 nrad. This method offers a feasible approach and serves as a reference for ground testing and in-orbit sensor calibration of space-based gravitational wave detection telescopes.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 230234 (2024)
Decoupling study and noise analysis of multi-degree-of-freedom deformation measurement method for space gravitational wave detection telescope
Jian Luo, Jie Song, Sijun Fang, Fanle Kong, and Yong Yan
The space gravitational wave telescope is a key payload of gravitational wave detection satellites, responsible for both beam expansion and compression. Optical path stability is a crucial indicator for the telescope, closely related to its structural stability. To meet the stringent requirements for ultra-high optical path stability and structural stability in gravitational wave detection missions, it is necessary to investigate the measurement of structural deformations in the telescope. This paper presents a study on multi-degree of freedom deformation measurement for space gravitational wave telescopes, focusing on addressing the coupling issues in multi-degree of freedom measurement and conducting a detailed analysis of error sources. During the development phase of the space gravitational wave telescope, this measurement method is expected to meet the demands for multi-degree of freedom deformation measurement, providing data feedback on multi-degree of freedom deformations for telescope design and offering guidance for optical path stability research. The space gravitational wave telescope is a key payload of gravitational wave detection satellites, responsible for both beam expansion and compression. Optical path stability is a crucial indicator for the telescope, closely related to its structural stability. To meet the stringent requirements for ultra-high optical path stability and structural stability in gravitational wave detection missions, it is necessary to investigate the measurement of structural deformations in the telescope. This paper presents a study on multi-degree of freedom deformation measurement for space gravitational wave telescopes, focusing on addressing the coupling issues in multi-degree of freedom measurement and conducting a detailed analysis of error sources. During the development phase of the space gravitational wave telescope, this measurement method is expected to meet the demands for multi-degree of freedom deformation measurement, providing data feedback on multi-degree of freedom deformations for telescope design and offering guidance for optical path stability research.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 230211 (2024)
Reinforcement learning-based stray light suppression study for space-based gravitational wave detection telescope system
Ziyang Zhang, Jun Chang, Yifan Huang, Qinfang Chen, and Yunan Wu
In gravitational wave telescopes, the energy of the collected space target light signals is dwarfed by the energy of stray light, necessitating robust stray light suppression for reliable telescope operation. Due to the inherent unpredictability of scattered light and the intricate nature of opto-mechanical systems, the formulation of stray light suppression strategies often involves complex mathematical modeling, substantial expertise, and iterative simulations. This paper introduces a Reinforcement Learning-based approach to devise the stray light suppression scheme within a Monte Carlo ray tracing environment, specifically for space gravitational wave telescope systems. Our empirical findings confirm the efficacy of this methodology in generating effective stray light suppression strategies, yielding favorable suppression performance. This study contributes a novel, efficient, and adaptable solution to the stray light challenges faced in space gravitational wave detection as well as other high-precision optical systems, thereby holding extensive applicative promise. In gravitational wave telescopes, the energy of the collected space target light signals is dwarfed by the energy of stray light, necessitating robust stray light suppression for reliable telescope operation. Due to the inherent unpredictability of scattered light and the intricate nature of opto-mechanical systems, the formulation of stray light suppression strategies often involves complex mathematical modeling, substantial expertise, and iterative simulations. This paper introduces a Reinforcement Learning-based approach to devise the stray light suppression scheme within a Monte Carlo ray tracing environment, specifically for space gravitational wave telescope systems. Our empirical findings confirm the efficacy of this methodology in generating effective stray light suppression strategies, yielding favorable suppression performance. This study contributes a novel, efficient, and adaptable solution to the stray light challenges faced in space gravitational wave detection as well as other high-precision optical systems, thereby holding extensive applicative promise.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 230210 (2024)
Research progress on numerical simulations of long space laser propagation
Zheyi Hua, Zhaorui Xu, Shaojing Peng, Ye Liu, Chong Liu, Lan Wu, and Dong Liu
This paper mainly introduces the development of space gravitational wave transmission and laser propagation in space gravitational wave detection. We profile the calculation methods used in the simulation of laser propagation and jitter noise in space-based laser interferometry. Compared with ground detection, space gravitational wave detection can effectively reduce noise and increase the length of the interference arm to realize high-precision gravitational wave detection. Under the distance of millions of kilometers and the precision requirements of the picometer level, it is necessary to consider the phase noise caused by pointing jitter with the telescope. Research has shown that defocus and astigmatism are the main aberrations affecting jitter noise at a distance of 2.5×109 m. There is a deviation between the phase stationary point and the origin position. To minimize the phase noise, the telescope angle needs to be adjusted. The gravitational wave detection at the phase stationary point can effectively reduce the phase noise and the requirements of the telescope exit pupil wavefront RMS. The large defocus and small coma can make the phase stationary point close to the optical axis and increase the received laser power. This paper mainly introduces the development of space gravitational wave transmission and laser propagation in space gravitational wave detection. We profile the calculation methods used in the simulation of laser propagation and jitter noise in space-based laser interferometry. Compared with ground detection, space gravitational wave detection can effectively reduce noise and increase the length of the interference arm to realize high-precision gravitational wave detection. Under the distance of millions of kilometers and the precision requirements of the picometer level, it is necessary to consider the phase noise caused by pointing jitter with the telescope. Research has shown that defocus and astigmatism are the main aberrations affecting jitter noise at a distance of 2.5×109 m. There is a deviation between the phase stationary point and the origin position. To minimize the phase noise, the telescope angle needs to be adjusted. The gravitational wave detection at the phase stationary point can effectively reduce the phase noise and the requirements of the telescope exit pupil wavefront RMS. The large defocus and small coma can make the phase stationary point close to the optical axis and increase the received laser power.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 230185 (2024)
Design and thermal stability analysis of primary mirror assembly for space-borne gravitational wave telescope
Sijun Fang, Bohong Li, Bin He, Yuwei Wu, and Lei Fan
In order to meet the application requirements of pimi-level stability and λ/30 wavefront error in space gravitational wave detection, an optical and mechanical integrated analysis and optimization method is proposed. Firstly, the position analysis of the support points on the main mirror side and the topology optimization of the support structure were carried out. Then, based on the flexibility matrix of parallel Bipod linkage support, the evaluation function of each structure parameter is established, and the value range of flexible support size parameters was preliminarily determined by Matlab analysis. Finally, an integrated optical and mechanical simulation platform was built to further optimize the structure.The results show that the first-order frequency of the system is 392.23 Hz, and the deformation of the primary mirror surface deformation under gravity and temperature loads is better than λ/60. Under thermal disturbances in a space environment of 10 μK/Hz1/2, the dimensional stability of the primary mirror component is at a level of 10 pm/Hz1/2. In order to meet the application requirements of pimi-level stability and λ/30 wavefront error in space gravitational wave detection, an optical and mechanical integrated analysis and optimization method is proposed. Firstly, the position analysis of the support points on the main mirror side and the topology optimization of the support structure were carried out. Then, based on the flexibility matrix of parallel Bipod linkage support, the evaluation function of each structure parameter is established, and the value range of flexible support size parameters was preliminarily determined by Matlab analysis. Finally, an integrated optical and mechanical simulation platform was built to further optimize the structure.The results show that the first-order frequency of the system is 392.23 Hz, and the deformation of the primary mirror surface deformation under gravity and temperature loads is better than λ/60. Under thermal disturbances in a space environment of 10 μK/Hz1/2, the dimensional stability of the primary mirror component is at a level of 10 pm/Hz1/2.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 230157 (2024)
Comparative study of detection modes for space-based gravitational wave observation
Jingui Wu, Xiaoyong Wang, Shaojun Bai, Kailan Wu, Zhongkai Guo, Yongchao Zheng, Yun Wang, and Xuling Lin
In order to achieve the measurement of gravitational wave signals in the millihertz frequency band, the space-based gravitational wave detection projects such as LISA, TianQin, and Taiji projects, which are based on laser interference systems, require the hardware noise floor of the interferometers to be lower than the interstellar weak light shot noise limit. This imposes stringent engineering specifications on the optical-mechanical design and the corresponding interferometer payload. This paper approaches the issue from the perspective of detection mode selection and derives the expressions of readout noise and stray light noise in the interference signal under the single detector mode and the balanced mode. Furthermore, a detailed discussion is provided on the weak-light interference process of the scientific interferometer. The results demonstrate that the balanced mode is capable of suppressing the interference phase noise caused by laser power fluctuations and backscattered stray light across multiple orders of magnitude. However, the suppression capability is constrained by the unequal splitting property of the beam combiner. To address this, a relative gain factor is introduced to compensate for the unequal splitting property of the beam combiner. Further analysis reveals that electronic gain compensation can only eliminate the impact of unequal splitting on one of the two noises rather than both simultaneously. Therefore, a balance must be struck in selecting gain compensation between the suppression of laser power fluctuation noise and stray light noise. Even with this consideration, the balanced mode still offers significant noise suppression capabilities at a magnitude difference, thus potentially reducing the engineering requirements for laser power fluctuations and telescope backscattered stray light. In order to achieve the measurement of gravitational wave signals in the millihertz frequency band, the space-based gravitational wave detection projects such as LISA, TianQin, and Taiji projects, which are based on laser interference systems, require the hardware noise floor of the interferometers to be lower than the interstellar weak light shot noise limit. This imposes stringent engineering specifications on the optical-mechanical design and the corresponding interferometer payload. This paper approaches the issue from the perspective of detection mode selection and derives the expressions of readout noise and stray light noise in the interference signal under the single detector mode and the balanced mode. Furthermore, a detailed discussion is provided on the weak-light interference process of the scientific interferometer. The results demonstrate that the balanced mode is capable of suppressing the interference phase noise caused by laser power fluctuations and backscattered stray light across multiple orders of magnitude. However, the suppression capability is constrained by the unequal splitting property of the beam combiner. To address this, a relative gain factor is introduced to compensate for the unequal splitting property of the beam combiner. Further analysis reveals that electronic gain compensation can only eliminate the impact of unequal splitting on one of the two noises rather than both simultaneously. Therefore, a balance must be struck in selecting gain compensation between the suppression of laser power fluctuation noise and stray light noise. Even with this consideration, the balanced mode still offers significant noise suppression capabilities at a magnitude difference, thus potentially reducing the engineering requirements for laser power fluctuations and telescope backscattered stray light.
Opto-Electronic Engineering
- Publication Date: Feb. 29, 2024
- Vol. 51, Issue 2, 230134 (2024)
Microlens array machining method based on projection lithography
Jianwen Gong, Jian Wang, Junbo Liu, Haifeng Sun, and Song Hu
A method for preparing microlens arrays based on projection lithography was proposed, and microlens arrays of various calibers and different surface roughness were successfully prepared by the method. The method employs a 0.2× projection objective lens to reduce the manufacturing cost of masks and realize the preparation of microlens arrays with different calibers. We achieve superior surface figure accuracy while reducing the complexity of mask preparation by employing a projection-based mask-shift filtering technique. Four kinds of microlens arrays with different calibers, 50 μm, 100 μm, 300 μm and 500 μm, were prepared. The machining accuracy of the surface morphology reaches the sub-micron level and the surface roughness reaches the nanometer level. The experimental results show that this method has great potential in the fabrication of microlens arrays, and can achieve lower line width and higher surface profile accuracy than traditional methods. A method for preparing microlens arrays based on projection lithography was proposed, and microlens arrays of various calibers and different surface roughness were successfully prepared by the method. The method employs a 0.2× projection objective lens to reduce the manufacturing cost of masks and realize the preparation of microlens arrays with different calibers. We achieve superior surface figure accuracy while reducing the complexity of mask preparation by employing a projection-based mask-shift filtering technique. Four kinds of microlens arrays with different calibers, 50 μm, 100 μm, 300 μm and 500 μm, were prepared. The machining accuracy of the surface morphology reaches the sub-micron level and the surface roughness reaches the nanometer level. The experimental results show that this method has great potential in the fabrication of microlens arrays, and can achieve lower line width and higher surface profile accuracy than traditional methods.
Opto-Electronic Engineering
- Publication Date: Jan. 19, 2024
- Vol. 50, Issue 12, 230281-1 (2024)
A multi-target semantic segmentation method for millimetre wave SAR images based on a dual-branch multi-scale fusion network
Junhua Ding, and Minghui Yuan
There are several major challenges in the detection and identification of contraband in millimetre-wave synthetic aperture radar (SAR) security imaging: the complexities of small target sizes, partially occluded targets and overlap between multiple targets, which are not conducive to the accurate identification of contraband. To address these problems, a contraband detection method based on dual branch multiscale fusion network (DBMFnet) is proposed. The overall architecture of the DBMFnet follows the encoder-decoder framework. In the encoder stage, a dual-branch parallel feature extraction network (DBPFEN) is proposed to enhance the feature extraction. In the decoder stage, a multi-scale fusion module (MSFM) is proposed to enhance the detection ability of the targets. The experimental results show that the proposed method outperforms the existing semantic segmentation methods in the mean intersection over union (mIoU) and reduces the incidence of missed and error detection of targets. There are several major challenges in the detection and identification of contraband in millimetre-wave synthetic aperture radar (SAR) security imaging: the complexities of small target sizes, partially occluded targets and overlap between multiple targets, which are not conducive to the accurate identification of contraband. To address these problems, a contraband detection method based on dual branch multiscale fusion network (DBMFnet) is proposed. The overall architecture of the DBMFnet follows the encoder-decoder framework. In the encoder stage, a dual-branch parallel feature extraction network (DBPFEN) is proposed to enhance the feature extraction. In the decoder stage, a multi-scale fusion module (MSFM) is proposed to enhance the detection ability of the targets. The experimental results show that the proposed method outperforms the existing semantic segmentation methods in the mean intersection over union (mIoU) and reduces the incidence of missed and error detection of targets.
Opto-Electronic Engineering
- Publication Date: Jan. 19, 2024
- Vol. 50, Issue 12, 230242-1 (2024)
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