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从理论上分析了超短激光脉冲在二阶非线性晶体中光整流效应产生THz辐射的过程,讨论了影响激光能量转换为THz辐射能量的效率的各种因素;入射激光脉冲宽度对转换效率影响非常大.对于一般二阶非线性晶体,当晶体厚度等于相干长度Lc时,光对THz的转换效率最高.对于周期性极化的非线性晶体,在忽略介质吸收的情况下,转换效率与介质厚度成正比.考虑介质对THz的吸收,晶体的有效长度Leff=0.63/α,再增大晶体长度,转化效率将没有明显增加,并最终趋于常数.
The process of THz radiation produced by ultrashort laser pulses in the second-order nonlinear crystal is theoretically analyzed. The factors affecting the efficiency of laser energy conversion to THz radiation energy are discussed. The effect of incident laser pulse width on the conversion efficiency Is very large.For general second-order nonlinear crystals, when the crystal thickness is equal to the coherence length Lc, the conversion efficiency of light to THz is the highest.For a periodically polarized nonlinear crystal, ignoring the absorption of the medium, the conversion efficiency and the medium Considering the absorption of THz by the medium, the effective length of the crystal Leff = 0.63 / α, and then increase the crystal length, the conversion efficiency will not significantly increase, and eventually tends to constant.