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Lensless cameras are characterized by several advantages (e.g., miniaturization, ease of manufacture, and low cost) as compared with conventional cameras. However, they have not been extensively employed due to their poor image clarity and low image resolution, especially for tasks that have high requirements on image quality and details such as text detection and text recognition. To address the problem, a framework of deep-learning-based pipeline structure was built to recognize text with three steps from raw data captured by employing lensless cameras. This pipeline structure consisted of the lensless imaging model U-Net, the text detection model connectionist text proposal network (CTPN), and the text recognition model convolutional recurrent neural network (CRNN). Compared with the method focusing only on image reconstruction, U-Net in the pipeline was able to supplement the imaging details by enhancing factors related to character categories in the reconstruction process, so the textual information can be more effectively detected and recognized by CTPN and CRNN with fewer artifacts and high-clarity reconstructed lensless images. By performing experiments on datasets of different complexities, the applicability to text detection and recognition on lensless cameras was verified. This study reasonably demonstrates text detection and recognition tasks in the lensless camera system, and develops a basic method for novel applications.Aimed at the slow detection speed and low measurement accuracy of wavefront aberration in current wavefront sensorless adaptive optic technology, different convolution neural networks (CNNs) are established to detect the turbulence wavefront, including an ordinary convolutional neural network, a ResNet network, and an EfficientNet-B0 network. By using the nonlinear fitting ability of deep neural networks, the mapping relationship between Zernike coefficients and focal degraded image can be established. The simulation results show that the optimal network model after training can quickly and efficiently predict the Zernike coefficients directly from a single focal degraded image. The root-mean-square errors of the wavefront detection accuracy of the three networks are 0.075λ, 0.058λ, and 0.013λ, and the time consumed for predicting the wavefront from the single degraded image are 2.3, 4.6, and 3.4 ms, respectively. Among the three networks presented, the EfficientNet-B0 CNN has obvious advantages in wavefront detection accuracy and speed under different turbulence intensities than the ordinary CNN and ResNet networks. Compared with the traditional method, the deep learning method has the advantages of high precision and fast speed, without iteration and the local minimum problem, when solving wavefront aberration.The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO). In these systems quasi-static aberrations need to be highly corrected and calibrated. To achieve this, the pupil-modulated point-diffraction interferometer (m-PDI) was presented in an earlier paper. This present paper focuses on m-PDI concept validation through three experiments. First, the instrument's accuracy and dynamic range are characterized by measuring the spatial transfer function at all spatial frequencies and at different amplitudes. Then, using visible monochromatic light, an AO control loop is closed on the system's systematic bias to test for precision and completeness. In a central section of the pupil with 72% of the total radius, the residual error is 7.7 nm rms. Finally, the control loop is run using polychromatic light with a spectral FWHM of 77 nm around the R-band. The control loop shows no drop in performance with respect to the monochromatic case, reaching a final Strehl ratio larger than 0.7.A periodic metasurface composed of a single layer of copper structure is proposed. The general transmission power beam splitter is composed of a multilayer structure, which is difficult to fabricate. The proposed single-layer terahertz wave power beam splitter contains only a single-layer circular hole cell structure, and it can control the transmission angle by controlling the arrangement mode of the coding cells. At the same time, we can control the transmission angle and the transmitted energy distribution of each beam based on different incident angles. A simple monolayer round-hole metasurface was prepared and its transmission characteristics were analyzed based on a terahertz time domain spectrometer. Compared with traditional splitter devices, our coding metasurface beam splitters with a single layer have the potential to promote the development of integrated optical systems.Herein, we studied the increasing tendency of photoacoustic (PA) conversion efficiency of the Au/polydimethylsiloxane (PDMS) composite. The thickness of the Au layer was optimized by modeling the PA process based on the Drude-Lorentz model and finite element analysis method, and corresponding results were verified. The results showed that the optimal Au thickness of the Au/PDMS composite was 35 nm. Finally, the Au/PDMS composites were coated onto the surface of aluminum alloys, which improved the thermoelastic laser ultrasonic (LU) signals to near 100 times. Besides, the defect mapping was performed by thermoelastic LU signals with Au/PDMS coating and ablation LU signals without coating; the Pearson correlation coefficient was higher than 0.95. The application in the defect detection in metal could provide guides for nondestructive detection on metals by laser ultrasound.Due to potential applications in next generation high-capacity wireless communication systems, generating and controlling vortex beams carrying orbital angular momentum (OAM) has received considerable attention. selleck chemical In this work, a scheme is proposed to generate two/four splitting vortex beams and focusing vortex beams with different topological charges under left circularly polarized and right circularly polarized terahertz waves under incidence. The meta-unit cell consists of a two-flying-fish-shaped patterned metallic top layer and an identical metallic patterned bottom layer separated by a silica layer. Full-wave simulation results agree well with that of calculation predictions. The proposed terahertz metasurface-based devices are able to carry different OAM modes and can abruptly manipulate during propagation, which indicates that such metasurface-based devices may have promising applications in terahertz wireless communication links in the future.We introduce a 405 nm external-cavity semiconductor laser using a volume Bragg grating (VBG) as the feedback element. By decreasing the length of the external cavity and reducing the wavelength difference between the output wavelength of the laser diode during free running and Bragg wavelength of the VBG, the emission wavelength of the semiconductor laser is stably locked at 405.1 nm with a spectral linewidth of 0.08 nm. The output power reaches 292 mW, and the wavelength drift with temperature reduces to 0.0006 nm/°C. These results are helping for the spectroscopy applications of a blue-violet laser diode. In contrast to traditional external-cavity semiconductor lasers, this laser is less expensive and more compact, in addition to having a narrow linewidth and good wavelength stability. These advantages would facilitate the development of associated areas of research, including optical data storage, laser display, and laser medicine.With the increase of the superimposed eigenmodes number, the traditional numerical modal decomposition (MD) technique will inevitably suffer from ambiguity and local minima problems and thus is typically unsuitable for conducting modal decomposition of an incoherent combined laser beam. In this paper, we propose a novel, to the best of our knowledge, MD algorithm, named ResNet-SPGD, which combines the advantages of residual networks (ResNet) and stochastic parallel gradient descent (SPGD) algorithm. Via setting the modal mode coefficients obtained from the CNN model as the initial value of the SPGD algorithm, such algorithm shows an attractive solution to mitigate the problem of modal ambiguity. The proposed algorithm is preliminarily applied to the modal decomposition of an incoherent combined laser beam, and the feasibility is demonstrated via numerical simulations. Complete MD is performed with high accuracy, and the only cost is the sacrifice of some real-time capacity.We study the influence rules of the speckle size of a light source on ghost imaging, and propose a type of speckle pattern to improve the quality of ghost imaging. The results show that image quality will first increase and then decrease with the increase in speckle size, and there is an optimal speckle size for a specific object. At the same time, by using a random distribution of speckle positions, a type of displacement speckle pattern is designed, and the imaging quality is better than that of random speckle patterns. These results are of great significance for finding the best speckle patterns suitable for detecting targets, which further promotes practical applications of ghost imaging.Infrared imaging is widely used in astronomical observation, medical diagnosis, and military applications. In recent years, metasurface technology has provided an unparalleled platform for the development of miniaturized and integrated infrared imaging systems. However, metasurfaces normally have inevitable chromatic aberration due to the high phase dispersion of the building blocks, which makes broadband achromatic infrared imaging difficult to realize. In this paper, we propose a polarization-insensitive metalens with a numerical aperture of 0.38 that can eliminate chromatic aberration for unpolarized incidences with the wavelength ranging from 3 to 5 µm. The simulated results show that within the design bandwidth, the proposed device achieves near-diffraction limit focusing and can increase the fill factor of infrared focal plane array pixels by 2.3 times, from 11.1% to 36.4%, with an excellent optical crosstalk performance of about 2.72%. Our work may pave the way for the practical application of achromatic metalenses in mid-wave infrared imaging equipment.We demonstrate a method for measuring a surface map of a spherical body with interferometric optical point sensors while rotating the test subject. The setup takes advantage of the excellent performance of heterodyne interferometry at nanometer levels and suppression of common-mode errors, as a cylindrical mirror mounted adjacent to the sphere is used as a reference. Future space based missions for gravitational wave research demand an improved inertial reference sensor with reduced acceleration noise levels. Spherical test masses can enable increased performance by suspension-free operation, contrary to cuboid solutions suffering from cross-coupling of attitude control noise into test mass position. However, interferometric readout is affected by surface irregularities and test mass attitude. An accurate surface map for compensation of the center of gravity readout should be established, by characterization either a priori or in-flight, when optical path length changes due to the surface occur in the measurement bandwidth.