The Study On Polarization Characteristics Of Coherent Combination In The Mutually Injection Corner-cube Cavity

The solid state laser has the characteristics of directionality,monochromaticity,good coherence and high brightness.It is widely used in scientific research,material processing,biomedicine,optical fiber communication and national defense security.Due to factors such as thermal effects,the output power of a single laser is always limited.High power density laser beams need to be accomplished by the combination techniques,and the coherent combination of multi-laser beams can obtain high quality and high average power laser beams.Therefore,the coherent combination of solid-state lasers is often achieved by mutual injection,and has become one of the research hotspots in the field of laser in recent years.The corner cube has self-collimating optical properties and can be used as the reflector of the resonant cavity to improve the stability and beam quality of the laser,in addition,the corner cube has six reflection paths and is often used in mutual injection coherent combination.However,when the light passes through the corner cube,the light will undergo three times of total internal reflection,and the polarization state of the light changes,eventually leading to a decrease in the efficiency of the coherent combination.In order to solve the depolarization effect of the corner cube,an elliptically polarized light correction scheme with the external wave plates is proposed,and this scheme is applied to verify the polarization-maintaining effect in the mutually injection corner-cube cavity.First,the basic methods for describing the polarization state are introduced: the polarization ellipse method,the Jones vector method and the Stokes parameters method,and the conversion relationships between three method are given.The ray coordinate system is defined according to the direction of light propagation,and the transformation relationship between coordinate systems is determined.The three reflection characteristics of the corner cube are given,and the Jones matrices describing the polarization characteristics of the corner cube is derived by the ray tracing method using Cartesian coordinate system.Then,by the diagonalization method of matrix,two maintaining polarization formulas are obtained when the light passes through the corner cube,with reflection paths of clockwise and counter-clockwise.This formula is used to maintain the polarization of the elliptically polarized light,and then calculate the refractive index range that satisfies the formula.According to the transformation formula between two ray coordinate systems,the Jones matrix of corner cube is simplified into two matrices,which are clockwise or counterclockwise,and the polarization-maintaining formula under other reflection paths is derived.Map the Jones matrix in the polarization-maintaining formula to the optical component,build the relevant optical path and test the polarization-maintaining effect: After correction,for linearly polarized incident light,the maximum absolute value of the ellipticity of the light in depolarization is reduced from 35° to 5°,When the incident light is the approximate circular polarization,its ellipticity drops from 44° to 40° after correction.Finally,the structure of the two-way mutual injection corner-cube cavity customized in the laboratory is analyzed.First calculate the eigen state of the cavity without the polarizer,then calculate the output polarization state when the polarizer is included and analyze the energy loss process caused by the depolarization of the corner cube.According to the polarization-maintaining formula,combine with the resonant cavity structure,the correction scheme is proposed and the polarization-maintaining device is made.The experimental results show that when the pump frequency of xenon lamp is 5Hz,the energy loss caused by depolarization is reduced to about 1.85%,but the fluctuation of the energy value is increased by about1%,after the polarization maintaining.The above results show that our laboratory has the ability to develop high-performance corner-cube cavity polarization-maintaining lasers.