利用各向同性半导体晶体差频产生可调谐THz辐射的理论研究

Study of tunable terahertz-wave generation via difference frequency mixing in isotropic semiconductor crystals

理论研究了利用剩余射线带色散补偿相位匹配原理,在Ⅲ-Ⅴ族和Ⅱ-Ⅳ族光学各向同性的半导体非线性晶体中差频产生可调谐THz波的可行性问题.根据这些半导体材料的色散特性,并以近简并点双共振KTP-OPO的可调谐相干双波长输出作为差频抽运源,对它们的相位匹配能力、差频增益特性、品质因数以及差频过程中的相干长度进行了理论分析和计算,确定了ZnTe晶体是在共线相位匹配情况下较为理想的THz波差频晶体,而InP晶体则更适合用于非共线相位匹配情况.

The tunable, coherent terahertz wave generation in a variety of isotropic semiconductor nonlinear crystals, such as Ⅲ- Ⅴand Ⅱ -Ⅳ compounds, by difference frequency mixing is studied theoretically based on the theory of the eross-Reststrahlen band dispersion compensation phase-matching. An angle-tuned, dual-wavelength KTP-OPO operating near the degenerate point is used as the pump source for THz wave generation. The theoretical analysis of phase-matching eonditions and coherence length for different materials mentioned above is presented according to their optical dispersion properties, and their gain characteristic and nonlinear figure of merit are also described and calculated. Through the theoretical analyses and calculations, it is shown that ZnTe is a promising DFG crystal for THz wave generation under the eollinear phase-matching condition, while InP is the one under the noneollinear phase-matching condition.