High energy 1064 nm Q-switched laser output is obtained by LD vertical array end pumping Nd:YAG. For different divergence angles of fast axis and slow axis of LD array, aspheric lens are used for beam shaping of LD array. The results show that light intensity distribution of output laser is very sensitive to the structure of the shaping system, which can be controlled by adjusting the spatial position of pumping, such as the distance between the aspheric lens pair, the distance between the front end of the crystal rod and the aspheric lens, and the approximate Gaussian beam was obtained without damage. When the distance between the aspheric lens pair is 24mm, the distance between the crystal rod and aspheric lens is 4mm, a 1064 nm Q-switched laser with single pulse energy of 80.8 mJ and pulse width of 10 ns was obtained
The high gain of pumping end in end-pumped all solid state lasers can easily cause self-excited oscillation, which limits the output energy of Q-switched laser. In order to obtain a 1064 nm Q-switched laser with high energy, high conversion efficiency and compact structure, the following three aspects are mainly studied to suppress the self-excited oscillation caused by the end pump: (1) the doping concentration of active particles is optimized to reduce the end gain of laser medium, (2) the wavelength of pump light is changed by adjusting temperature of laser diode to deviate from absorption peak of Nd:YAG, (3) Nd:YAG rod is processed by tapered side, which improves the difficulty of self-excited oscillation. By using the above techniques, a 1064 nm Q-switched laser with output energy of 100 mJ is obtained at a pump current of 20 Hz and 170 A, and the corresponding dynamic to static Q-switching ratio is 77%. The three technical means proposed in this study complement each other and work together, providing a practical and effective technical way for obtaining high-energy end pumped Q-switched laser.
In this paper, the finite element model of the fiber optic plates is established by using the finite element software. The simulation process is basically in line with the actual production process of the fiber optic plates. According to the simulation results, the deformation degree and speed of each part of the fiber optic plates in the process of melting pressure, as well as the changes of stress and strain of each part in the process of forming are analyzed. The results show that the deformation speed and degree of different parts are different in the process of melting pressure of fiber optic plates, especially the upper and lower end faces and side edges of fiber optic plates; and the stress and strain of each part are constantly changing, and the stress and strain values of the upper and lower end faces and side edges of fiber optic plates are larger than others.
The microchannel-plate-based x-ray optics is a spherical crown containing millions of square microchannels, reflecting the small incident angle light at a certain angle through the inner wall of the channels. Structure defects may exist in the square microchannel array. In this paper, the effects of structure defects on the imaging performance were studied through simulation and MPO preparation experiment. The structure defects involved in the paper include two types, chamfered channels and tilting channels. The experimental results are consistent with the simulation images, proving that the simulations are correct. The results show that the imaging of MPO with standard square channels array is a symmetrical cross. The presence of chamfers in corner of the channels results in a weak secondary small cross in the 45° direction of the obvious cross. For the case that the channels are tilted slightly, the center of the cross deviates from the imaging center, and the cross becomes an asymmetric cross. This study provides a theoretical guidance for precise control of array structures in the preparation of MPO.
The optical imaging system is the the core device in the extrem ultraviolet (EUV) astronomical telescope. Because of its light weight, large field of view, high resolution, the lobster-eye optical imaging system is considered to be the best imaging system for EUV. The curved square hole microchannel plate is an imitation lobster-eye type optical imaging system. The channels of the traditional curved square hole microchannel plate are generally arranged in a square shape, and the image is a cross image, which only the cross area is effectively detected, so the detection efficiency is low. In this paper, all the square hole channels are pointed to the center by radial arrangement, thereby the detection efficiency is improved. However, this arrangement cannot achieve close alignment, and there are a large number of voids in the structure, which reduces the density of the focusing unit. In this paper, the simulation of the radial arrangement of the square hole microchannel structure is carried out by Tracepro simulation software. Through the high-precision wire drawing method, radial arrangement technology, and distortion-free control, the drawing precision of the square wire is improved, the square wire structure defects are eliminated, and the square hole microchannel plate with uniform structural height is prepared.
Cracks in microchannel plate (MCP) seriously reduce the mechanical and electrical properties of MCP. The generation mechanism of cracks and the structure of sub-surface damage layer were revealed by studying the changes of surface morphology of MCP in optical process and chemical treatment process. The source of cracks appeared in the etching and reduction process is the sub-surface damage layer in the optical process. The damage layer includes cracks and non-uniform strain layer. After slicing, the depth of damage layer visible to optical microscope is within 25μm. During the polishing process, the damage layer is deeper, and there is a non-uniform strain layer with the depth of about 20μm. To avoid the occurrence of cracks, the thickness setting in the slicing process should take into account the slice damage layer, the polishing crack growth layer, and the strain layer.
As the core component of image intensifier, the electronic multiplication performance of microchannel plate determines the ability of the device to detect weak signals. The theoretical model of electron gain is the theoretical basis for the secondary electron multiplication of microchannel plates. It has important theoretical significance for the research of high performance microchannel plates and image intensifiers. In this paper, the theoretical model and simulation of electron gain in microchannel plates are reviewed. The electronic gain model and the modified theoretical model of the "energy proportional hypothesis" are emphatically introduced. On the basis of the model, some improvements are made and good simulation results are obtained. The behaviors of electron transport, collision and multiplication in microchannels based on the theoretical model of electronic gain and Monte Carlo stochastic calculation method are summarized. The differences among the three models are analyzed, and the problems existing in the theoretical model and simulation of electronic gain at present are analyzed. Finally, aiming at the shortcomings of theoretical model and simulation, the direction of improvement and optimization is put forward.
Electron scrubbing is an effective method of degassing the microchannel plate(MCP). In the present work, we investigated the effect of electron scrubbing on MCP through characterizing the gain and dynamic range during and after the electron scrubbing. The gain of the MCP decreases to 25-30% of the initial gain with 28μA·h of electron scrubbing. The dynamic range can be broadened by electron scrubbing. The lower limit of the dynamic range of the MCP limited by the dark current of the test system does not change significantly and the upper limit of the dynamic response range is increased. The ratio of the upper limit before and after scrubbing is inversely proportional to that of the gain. The reasons for variation of gain and dynamic range were discussed, to provide reference for improving the performance of microchannel plate.
All-solid-state lasers have become one of the most promising research fields in the field of lasers because of their small size, high efficiency and convenient operation. All-solid-state lasers use semiconductor lasers as pump sources, however, Compared with gas lasers, solid-state lasers and fiber lasers, high-power semiconductor lasers have poor beam quality, thus limiting the progress of all-solid-state lasers. Therefore, improving the power and beam quality of semiconductor lasers has become a bottleneck in the development of all-solid-state lasers. The unit beam of the semiconductor laser is rectangular, so the beam needs to be shaped and focused to form a spot before being coupled to the laser medium. Due to its poor quality the spot center has a high optical energy density. When using LD end-pumped mode, the spot can easily destroy the film of the working medium end. In this paper, a uniform function describing the distribution of refractive index and the related parameters were used. And use this function to simulate and calculate the transmission characteristics of optical fiber. Based on the influence of fiber refractive index and core structure on the distribution of optical power in cross section, the homogenization of the LD beam spot is achieved by designing the core structure of optical fiber. This paper established optical fiber transmission model of light waves by using Matlab software and confirmed the influence of the refractive index distribution on the optical power distribution by using Comsol Multiphysics software.
Based on the high-resolution imaging property of the products of optical fiber material, a novel imaging system is proposed. The prototype of the system is made by coupling CCD chip(CMOS) and a large-scale optical fiber faceplate together. Firstly, the working principle and manufacturing process of large-scale optical fiber faceplate is described. Secondly, the effectiveness and practicability of the prototype of the system is verified by experiment. Finally, the potential application prospect of the imaging system is discussed. The theoretical analysis and experimental result show that the prototype works perfectly under high temperature and pressure condition and the resolution of the image that obtained by the imaging system is larger than 70 lp/mm, which can satisfy the basic imaging requirements in the research fields such as medical diagnosis, industrial detection and monitoring. Further, the novel imaging system provides a new approach for the application of optical fiber product in scientific research.
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