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.
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.
The s parameter of the gain theory of microchannel plate directly affects the value of each secondary electron emission coefficient. The electron gain is the accumulation of all secondary electrons, so the s parameter has an important influence on the theoretical value of the electron gain. In this paper, two kinds of clad glass and the same core glass materials are used to fabricate two kinds of microchannel plates under the same process conditions, and measured the electronic gain values. Meanwhile, the theoretical model of the electronic gain of the microchannel plates is established by Monto Carlo stochastic mathematical method, and the s parameters of two kinds of microchannel plates were fitted by the model combined with the measured electronic gain values. On the fitted value of S parameters, the variation of the microchannel plates gain and electron transit time with the microchannel plates applied voltage at both ends, channel bias angle, channel length-to-diameter ratio and output electrode penetration depth is simulated, and compared with the corresponding measured results, the coincidence is high. The relationship between electron gain with bias angle and output electrode depth, and the relationship between Gain with Length/Diameter ratio under different voltage is obtained. Besides, this paper get the relationship between Electron transit time and Full width at half maximum (FWHM) with the different Voltages. The results of this study provide support for the calculation of theoretical electron gain of microchannel plates in different clad glass systems.
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