Properties Of ZnGeP₂ Mid-Infrared Laser System

This thesis has focused on research of a mid-infrared laser using nonlinear optical crystal supported by Beijing Nature Foundation (No.4062008), the properties of tunable mid-infrared OPO-DFG system based on the crystal of ZnGeP2(ZGP).The tunable broadband of mid-infrared laser source was generated that the mid-infrared laser crystal has broad prospects for the applications in the realm of military, environmental monitoring and biological medicine, etc.. Optical parameter frequency conversion in mid-infrared laser crystal is an effective method to obtain a tunable broadband mid-infrared output. Therefore, this research has not only definite theoretical signification, but also strong practical function. There are three research work emphases in this paper as follows.1. The background and significance of research work have been explained. The application introduction of mid-infrared light source in military and livelihood fields, and the nonlinear optical crystal is very useful in the mid-infrared laser have been summarized. In addition, the developing history of OPO and DFG with nonlinear optical crystal to obtain mid-infrared laser output has been reviewed.2. The crystal energy structure and optical characteristics of Yb:YAG have been discussed in detail. The output characteristics of Yb:YAG all-solid-state laser have been obtained by establishing the theoretical model of Q-switched in quasi-three-level laser system. The output characteristics have been studied by simulating with MATLAB program.3. Based on resonant three wave coupling equations, The basic principle of angle tunable in phasemaching type-I, and -II for a positive uniaxial crystal and negative uniaxial crystal have been theoretical analyzed and simulated. In addition, the principles of OPO and DFG with nonlinear optical crystal have been analyzed and compared. The optical properties of mid-infrared laser crystals and the tuning characteristics, parametric optics linewidth , acceptance angle, walk-off angle, conversion efficiency in the process of ZGP-DFG have been analyzed based on sellmeier equations of mid-infrared laser crystals and the theory of angle-phase-maching. Through numerical simulation with MATLAB, the curves of refractive index dispersion of ZGP and the curves of effective nonlinear coefficient, angle tuning and acceptance angle, walk-off angle for ZGP-DFG have been obtained and compared with relative crystal of AgGaSe2 (AGSe) and AgGaS2 (AGS). In addition, the relation curves of pump linewidth will influence DFG output linwidth, and the pump intensity, crystal length, phase-mismatch will influence the output conversion efficiency have been obtained, and compared with of AGSe and AGS. By making comparison of the three crystals, the conclusion was that: the tunable mid-infrared output of DFG with ZGP and AGSe were superior to AGS; in obtaining high conversion efficiency, ZGP was far superior to AGSe and AGS, which have been consistent with the experimental results in domestic and overseas researcher's. Therefore, ZGP has been approved to be an ideal nonlinear laser crystals for generating tunable mid-infrared coherent radiation.