Reaction-boned silicon carbide (RB-SiC) is considered a new material for large lightweight ground-based space telescopes due to its high specific stiffness, low thermal deformation, and excellent optical quality. The excellent mechanical properties of RB-SiC result in the low efficiency of traditional polishing and mechanical polishing. In this paper, a polishing method for RB-SiC based on a femtosecond laser is proposed to improve surface quality. A theoretical heat conduction model was established in the process of femtosecond laser irradiation of SiC. We analyzed the ablation type and calculated the single-pulse ablation threshold of SiC, which verified the feasibility of femtosecond laser polishing. Further, the effects of polishing parameters on the polished surface quality were analyzed by a series of experiments, and the optimal parameters were selected. It was observed to improve polishing efficiency and can replace the intermediate steps of traditional mechanical polishing.

The robust detection of small targets is one of the crucial techniques in an infrared system. It is still a challenge to detect small targets under complex backgrounds. Aiming at the problem where infrared small target detection is easily disturbed by complex backgrounds, an infrared single frame detection method based on a block-matching approach is proposed in this paper. Firstly, the input infrared image is processed by extracting blocks from it. A new infrared model is constructed by finding blocks that are similar to each such block. Then, the small target detection based on the block-matching model is formulated as an optimization problem of recovering low-rank and sparse matrices, which are effectively solved using robust principal component analysis. Finally, the results of processing are reconstructed to obtain the target and background images. A simple segmentation method is used to segment the target image. The experimental results from the actual infrared sequences show that the proposed method has better background suppression ability under complex backgrounds and better detection performance than conventional baseline methods.

Wavefront reconstruction and correction under strong turbulence has become a crucial issue for adaptive optics systems. An approach using a plenoptic sensor has attracted high attention recently. However, the existing reconstruction and correction algorithms based on the plenoptic sensor are sometimes unsatisfactory. Therefore, we propose a modified approach based on the checkerboard algorithm to reconstruct the wavefront. By means of a weighted summation, the reconstruction accuracy is clearly increased. We propose using the direct-gradient method to correct the disturbed wavefront after reconstruction, and our experimental results demonstrate the effectiveness with only one correction step.

Object tracking has become widespread in many fields, such as autonomous vehicles, video surveillance and robotics. However, it is far from the requirements for real-world applications. Recently, Siamese network based trackers have attracted high attention by balancing accuracy and speed. Because these trackers only learn a similarity measurement model via off-line training, the exemplar branch has insufficient discriminant information to adapt to the constantly changing appearance of the target in subsequent frames. We propose a Siamese network based tracker that improves upon tracking performance as follows. First, an adaptive background superposition initialization is proposed and used in the exemplar branch to make full use of the limited prior information in the first frame. Second, a light-weight convolutional neural network is proposed and applied as the tracker's backbone; it compresses the dimensions of the feature to ensure speed and accuracy. Third, the channel attention module is introduced into our tracker and integrated with adaptive background superposition initialization. The feature map of the original exemplar image and its background changed image are adjusted by a channel attention model and fused to enhance the representation of the exemplar image. The GOT-10k dataset is applied to train our tracker. Finally, experiments on the object tracking benchmark (OTB) and visual object tracking (VOT) demonstrate the effectiveness of our proposed approach compared with state-of-the-art trackers.

In this paper, we study the characteristics of the supercontinuum (SC) induced by the filamentation of two typical vortex beams (i.e., Laguerre-Gaussian (LG) and Bessel-Gaussian (BG) beams) in water. By moving the cuvette filled with water along the laser propagation path, we measure the SC induced by the filamentation of the two vortex beams at different positions in water. The results show that the degree of spectral broadening induced by the filamentation of LG beams hardly changes with the change of position, while for BG beams, the spectral broadening induced by filamentation is weak on both sides and strong in the middle. The value of topological charge (TC) affects the length of the filament formed by BG beams; however, its effect on the spectral broadening induced by the filamentation of LG and BG beams is negligible.

Large survey telescopes are vital for mapping dark energy and dark matter in the deep universe. This study presents a fiber-linked internal motion metrology system that aligns the mirrors and large lenses in the telescopes to enhance alignment accuracy by improving the image quality at a lower weight, volume, power, and cost. The internal motion system comprises a photonic laser beam projector capable of projecting multiple Gaussian beams onto the detector of the telescope. The specific spatial frequency aberration component is determined by combining Gaussian beam location and the geometry model of the telescope. Furthermore, integrating the proposed system with the curvature-sensing wavefront system enables more precise alignment and camera sensing. In the experimental tests, the location precision was within 10 μm, and the rotation precision improved to 5 arcsecs, fulfilling the alignment and motion monitoring requirements of large survey telescopes. The results of this study can be used as a reference to improve the performance of closed-loop bandwidth systems and active camera optics.