Rongkuan Leng

With the continuous advancement of technology, the manufacturing standards for optical components have become increasingly stringent. Due to variations in material properties, achieving satisfactory surface roughness on certain materials remains challenging. Researchers have employed surface modification techniques to alter the properties of substrate surfaces, resulting in enhanced polishing precision on modification layers. However, subsequent investigations have revealed that during the precise figuring of these ultra-smooth, damage-free modification layers, a significant number of defect structures emerge on the surface, leading to a marked increase in surface roughness and severely limiting ultimate machining precision. To address these issues, this study focuses on ion beam figuring (IBF) as a case study. It first elucidates the mechanisms of material removal from the modification layer surface during IBF through microscopic characterization techniques and molecular dynamics (MD) simulations. Microscopic analysis indicates that the morphology of the substrate significantly influences the properties of the modification layer. The MD simulation results demonstrate that variations in the properties of the modification layer contribute to discrepancies in local sputtering yields, which in turn lead to the formation of surface defects. Finally, based on these findings, a method for achieving ultra-smooth, damage-free fabrication of modification layer surfaces is proposed, and its feasibility is experimentally validated. The results demonstrate that modification layers grown on smooth, defect-free substrates exhibit superior quality, with surface roughness remaining below 0.2 nm RMS after figuring, while maintaining an ultra-smooth and damage-free state.

In recent years, the application of gas cluster ion beam (GCIB) technology has made great progress. Due to the similar essence of a monoatomic ion beam, the GCIB also shows flashes of brilliance in material processing. It has been reported that smoothness can be greatly improved after the rough surface is bombarded by the GCIB. This indicates that the GCIB processing has great potential in optical fabrication. Although the surface smoothing effect has been investigated, there is still a lack of dynamic micro-analysis for GCIB processing, which is limited for better understanding the mechanism of smoothing effect. In this paper, the surface smoothing effect in GCIB processing is explicitly investigated with molecular dynamics (MD) simulation and experiment. The principle of GCIB processing is compared with the traditional monoatomic ion-beam based processing, and details of the MD simulation procedure are introduced. Based on this, the dynamic micro-analysis of GCIB processing is conducted under different processing conditions. The simulations reveal the phenomena of atomic removal and migration in GCIB processing, which plays an important role in explaining the mechanism of surface smoothing effect. The experiment was performed on the silicon substrate with the in-house GCIB processing machine. The results indicate that the initial rough surface with dense protrusions can be greatly smoothed, and the root mean square (RMS) value is reduced from 0.586 nm to 0.191 nm. Both simulation and experiment can provide a better understanding of smoothing effect mechanism in GCIB processing.

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed 《中国光学》的前身是1985年创办的《中国光学与应用光学文摘》，当时是国内光学领域唯一的检索刊物。2008年底《中国光学与应用光学文摘》转型更名为《中国光学与应用光学》期刊，刊载内容突破了文摘的限制，正式成为学术刊物。

Surface imperfections or contamination on an optical smooth surface is usually inevitable and causes scattering. The directional information of the scattered ray can be related to the spatial frequency through the grating equation. On the other hand, the layout of the optical system determines whether a scattered ray will finally reach the detector according to the positions and directions of the scattered rays. Therefore, the scattering propagation in an optical system is usually band-limited and the effective optical range differs for different systems. In this paper, a method based on ray tracing is described that can statistically determine the optical scattering and the band of roughness. The results can be an essential reference for optical surface polishing and contamination control.

Space-based gravitational wave detection programs, such as the Laser Interferometer Space Antenna (LISA) or Taiji program, obtain gravitational wave signals by measuring the change in the distance between three satellites by laser. The telescope is an important part of the measurement system, and its function is to transmit and receive laser signals. Due to changes in the space environment, the telescope will inevitably introduce additional dynamic aberrations, which will bring optical path errors to the inversion of gravitational wave signals. Taking LISA as an example, to achieve pm-level measurement accuracy at the detection frequency of 0.1 mHz–1 Hz, the stability requirements of the telescope are less than 1 pm/Hz^1/2. This paper theoretically deduces the aberration types that affect the telescope’s stability and conducts simulation analysis according to the actual phase demodulation method, which verifies the theory’s correctness. In addition, using this theory, it can be concluded that under the condition that the total size of the telescope aberration is determined to be stable, reducing the ratio of rotationally symmetric aberrations such as “spherical aberration” and “defocusing” among common aberrations can significantly improve the stability of the telescope. The conclusion guides the optical system design of LISA or Taiji.

In many optical engineering applications, a spherical cap shaped optical element is widely used such as concave or convex mirrors in reflective optics. Such an element can also tilt around the vertex which corresponds to an off-axis optical design. The optical backscattering of such an optical element sometimes could be important. For example, in the space-based gravitational wave detection, the backscattering of such an element could be superimposed with the local oscillator and limits the sensitivity of the spacecraft. The scattered contributions depend on the scattering property of the mirror surfaces and the geometrical arrangement including the radius of curvature, the tilt and the interval between the scattering source and detector plane. Based on random estimation method, this paper starts from the radiometry, combines these variables and calculates the theoretical amount of back scattered light for both diffuse and superpolished surfaces. The results are compared with analytical and ray tracing solution. The conclusions can be used to further improve the optical design of the telescope or extended to other cases where the backscattered light should be controlled.