Modeling and numerical simulation of a semiconductor switching device applied in an ultra-short pulse CO2 laser
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摘要: 本文开展了基于半导体光开关技术实现超短脉宽CO2激光输出的物理机制研究。首先，在分析光生载流子过程及载流子复合扩散机制的基础上，引入直接吸收、俄歇复合、等离激元辅助复合以及双极扩散等物理过程，并基于Drude理论，完善了半导体光开关理论模型。其次，利用该模型对两级半导体光开关产生超短CO2脉冲机制进行了数值模拟及分析，结果显示该模型与国外最新实验结果一致，表明了模型的合理性与正确性。最后，利用该模型分析了控制光脉冲宽度对两级光开关工作效率的影响，发现短的控制光脉冲更有利于精确、高效地截取出高质量的超短CO2脉冲。本文研究证明半导体光开关法是实现超短CO2激光脉宽可调输出的有效技术途径。Abstract: The physical mechanism are studied for ultra-short pulse CO2 laser output realized by semiconductor switching technology. Firstly, based on the analysis of the generation, recombination and diffusion mechanism of laser-produced carriers, we introduce direct absorption, Auger recombination, plasmon-assisted recombination, an ambipolar diffusion process and according to Drude theory, we improve the theoretical model of semiconductor switching. Secondly, we simulate and analyze the generation of ultra-short CO2 pulses by two-stage semiconductor optical switches employing this model. The results show that the model is in good agreement with the latest experimental results reported abroad, which implies the rationality and correctness of the model. Finally, the model is used to analyze the effect of control pulse duration on the efficiency of the two-stage switching. It is found that a short control pulse is more conducive to intercepting high-quality ultra-short CO2 pulses accurately and efficiently. Semiconductor switching is an effective technique to realize the output of an ultra-short CO2 laser with an adjustable pulse width.
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Key words:
- CO2 laser /
- semiconductor switching /
- laser-produced plasma /
- ultra-short pulse
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图 1 (a)反射光开关(b)透射光开关示意图
Figure 1. Schematic diagrams of (a) reflection switch (b) transmission switch.
图 2 脉宽为20 ps，能量密度为0.6 mJ/cm2，波长为1.06 μm控制光脉冲辐照下半导体表面等离子体密度随时间变化曲线
Figure 2. Surface density of plasma in germanium plotted as a function of time under the radiation of 1.06-μm control pulse with pulse width of 20 ps and energy density of 0.6 mJ/cm2.
图 3 控制光消失后表面等离子体密度随时间变化曲线
Figure 3. Surface density of plasma in germanium plotted as a function of time after the control pulse vanishing
图 4 CO2光脉冲垂直入射反射光开关输出脉冲能量变化曲线
Figure 4. Calculated vertical reflected pulse energy plotted as a function of time
图 5 CO2光脉冲以布鲁斯特角入射反射光开关输出脉冲能量变化
Figure 5. Calculated Brewster′s angle reflected pulse energy plotted as a function of time
图 6 单级半导体反射开关输出的CO2光脉冲
Figure 6. CO2 pulse output from single-stage semiconductor switching
图 7 单级半导体反射开关表面等离子体密度随时间变化曲线
Figure 7. Surface density of plasma in single-stage semiconductor switching plotted as a function of time
图 8 两级半导体光开关在5、10、15、20 ps延迟时间下输出CO2脉冲能量
Figure 8. CO2 pulse energy outputs from two-stage semiconductor switching with time delay of 5, 10, 15 and 20 ps
图 9 脉宽为6、10、30、60 ps的控制光脉冲辐照单级反射开关得到CO2脉冲能量
Figure 9. CO2 pulse energies obtained by using controlled light pulse with pulse widths of 6, 10, 30, 60 ps to radiate single–stage reflection switch
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