Study On Tm:LuAg Single Longitudinal Mode Laser Interferometer For Measuring Refractive Index Homogeneity Of ZGP Crystal

The 3⁵?m laser is in the transparent window of the atmosphere and the band of the thermal radiation concentration of the object,it has special applications in infrared guidance and optoelectronic countermeasures,which can not be replaced by other band lasers.ZnGeP₂?ZGP?crystal is a commonly used nonlinear crystal to produce 3⁵?m infrared laser.Its refractive index homogeneity is one of the important indexes to measure the crystal properties.The measurement of refractive index homogeneity of ZGP crystal can provide a basis for the improvement of its growth process.In the past,researchers used commercial infrared interferometers to measure the homogeneity of crystal folding rate directly,but this kind of interferometer is very expensive and complex in structure,so it can not be widely used in basic experiments.The purpose of this paper is to design and build a set of simple Tm:LuAG single longitudinal mode laser interferometer to meet the basic measurement needs of the laboratory under the existing experimental conditions,and to apply this interferometer to the measurement experiment of refractive index homogeneity of ZGP crystal.The main contents of this paper are as follows:1.The characteristics of common interference methods for measuring refractive index homogeneity of crystal and the analysis methods of measurement results are analyzed,aiming at the measurement of refractive index homogeneity of ZGP crystal,the 2.02?m laser output from Tm:LuAG single longitudinal mode laser is selected as the interference light source.The interference structure adopts Mach-Zendell type,and the refractive index homogeneity of ZGP crystal is obtained by the change of interference fringes.By comparing the common methods to obtain single longitudinal mode laser,this paper adopts the one way annular cavity method based on Faraday effect,and uses Faraday rotator and half wave plate to realize the one way operation of ring cavity,thus producing single longitudinal mode laser.The principle of air wedges equal thickness interference produced by Mach-Zendell interference structure and the characteristics of interference fringes are analyzed.The quantitative relationship between the variation of fringes and the refractive index homogeneity of crystals is deduced theoretically.2.The experimental device of interferometer is built.The single longitudinal mode laser is obtained when the ring cavity Tm:LuAG laser operates in one way.The maximum output power is 511mW,the wavelength is 2022.40nm,and the M² factor of beam quality is 1.2.The interferometric image is obtained by beam analyzer,and the interferometric fringes are processed and calculated by the national standard method.The measuring accuracy of refractive index homogeneity of ZGP crystal is 2.5×10^-6.The refractive index homogeneity of 16 ZGP crystals is measured by the interferometer,and the quality of ZGP crystal is screened according to the refractive index homogeneity.In this paper,2?m single longitudinal mode laser is used to detect the refractive index homogeneity of ZGP crystal for the first time.A Tm:LuAG single longitudinal mode laser interferometer is designed and successfully built,and the refractive index homogeneity of ZGP crystal is measured.