The SiO2-B2O3-La2O3-BaO glass has emerged as an important material due to its high performance. The effect of BaO content on the properties of SiO2-B2O3-La2O3-BaO glass such as density, thermal expansion coefficient, refractive index, and transmissivity were systematically studied. The results indicate that BaO content had influence on the density, refractive index and thermal expansion coefficient of the SiO2-B2O3-La2O3-BaO glass, BaO content did not have obvious impact on the transmissivity of SiO2-B2O3-La2O3-BaO glass.
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.
For reducing the self-excited oscillation of end-pumped laser, the laser properties of the end-pumped Nd:YAG Q-switched laser is investigated with different Nd3+ ion doping concentration. The experiment results indicate that the output energy of the end-pumped Nd:YAG Q-switched laser is saturated when the pump energy is greater than 467mJ with 0.6% Nd3+ ion doping concentration, and the maximum output energy of 62.9mJ is generated under the pump energy of 498mJ, corresponding to the optical conversion efficiency of 12.6%. When the Nd3+ ion doping concentration decreases to 0.4%, the output energy of the end-pumped Nd:YAG Q-switched laser increases continuously with increasing pumping energy, the output energy is up to 64.7mJ under the pump energy of 498mJ, corresponding to the optical conversion efficiency of 13.0%, and no saturation occurs. By optimizing the structure parameters of the pump system, a 82.1mJ 10ns 1064nm laser is obtained under the pump energy of 527mJ, corresponding to the optical conversion efficiency of 15.6%. In view of the saturation of output energy in the end-pumped Nd:YAG Q-switched laser, Nd3+ ion doping concentration adjustment is carried out to reduce the pump end-face gain of laser medium, the self-excited oscillation can be effectively suppressed, an effective technical means for obtaining high-energy end-pumped Q-switched laser output is provided.
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 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.
Crack in microchannel plate (MCP) seriously reduces the mechanical and electrical properties of MCP. The mechanism of crack propagation in the chemical treatment process was revealed by studying the changes of crack morphology in acid-alkali etching and hydrogen reduction. The results show that during the acid-alkali etching process, the cracks on the channel material is dissolved by the dilute HNO3 and the cracks on the channel wall expands gradually under the etching of the NaOH solution. During the reduction process, cracks do not change significantly at the stage of heating. While at the stage of reaction with H2,the cracks are more easily expanded. The length of cracks does not change significantly after reduction. However, the surface near the cracks warps and the depth of cracks increases.
As an excellent two-dimensional electron multiplier device for transmission and enhancement of electronic image, microchannel plate (MCP) has the advantages of small volume, light weight, high resolution, high gain, low noise, low operating voltage, which plays an irreplaceable role in the fields of low-light-level night vision, space detection, nuclear detection, ultraviolet warning, medical image and so on. In recent years, with the continuous expansion of the application fields and the improvement of related manufacturing technologies, the performance requirements of MCP, especially the image quality, are getting higher and higher. 4G standard is the latest international requirements of image intensifier with FOM (Figure of Merit) reached more than 1800. Fixed pattern noise between multi-fibers of MCP is a common image defect. This defect not only increases the noise, reduces the signal-to-noise ratio, but also greatly interferes with the imaging quality, which has become a bottleneck problem restricting the improvement of FOM. This research is focused on the formation mechanism and control technology of fixed pattern noise between multi-fibers of MCP. The result shows that the formation mechanism of the fixed pattern noise between the multi-fibers is caused by the difference in microchannel structure, which leads to the difference in secondary electron yields between adjacent multi-fibers. Improving microchannel uniformity is an effective way to eliminate fixed pattern noise. The difference in microchannel structure is caused by the diameter deviation during fiber drawing. Through analysis and experimental measurement, it is found that the "heating-constant-cooling" zone of the drawing furnace has an optimal structure.
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