Theoretical Analysis Of The Ase Effect And Thermal Aberrations In Yb:YAG Thin-disk Lasers With The Influence Of Anti-ASE Cap

Yb:YAG thin-disk laser realizes the combination of high average power,high peak power and high beam quality.In recent years,it has already been one of the most popular and promising high power solid-state lasers in recent years.With the improvement of output power of thin-disk laser,the severe ASE effect has become the major factor that limits the scaling and beam quality.One of the effective approaches to suppress the ASE is anti-ASE cap.But there are still issues about the influence of different thickness anti-ASE cap on ASE effect and thermal-optical aberration of thin-disk laser.So,it is necessary to deeply analysis the role of anti-ASE cap with different thickness and develop the theoretical model of anti-ASE cap.This will be helpful to better choose an appropriate design scheme of anti-ASE cap thickness and other parameters of thin-disk.In this thesis,a constructed new disk is built to estimate the ASE photon flux density of thin disk crystal with different thickness anti-ASE cap.Based on the classical ASE photon flux density model,the analytical model of ASE with different thickness anti-ASE cap is updated.Combine this model with the quasi-three-level rate equations,the operational properties of thin disk laser with ASE effect such as upper level effective lifetime and output power density will be analyzed and presented intuitively.Moreover,temperature,stain and displacement fields will be obtained by using aberration diffraction loss theory and finite element analysis software COMSOL.The optical path difference(OPD)of the thin disk crystal is computed based on the obtained temperature and strain distribution.OPD is decomposed into spherical and aspheric terms aimed at specific fundamental mode(0.7R_P)field.The numerical model of fundamental mode diffraction loss associated with aspheric OPD with different thickness anti-ASE cap is built to analyze the thermal aberration of disk crystal with the influence of anti-ASE cap.Combined with previous analysis of ASE effect,a compromise scheme is given to choose an appropriate value of anti-ASE cap thickness and other disk parameters.After that,the suppression of beveled disk on ASE effect is briefly discussed.An analytical expression of side-ASE effect and beveled angle is estimated.Combined with the analysis of suppression of anti-ASE on top-face ASE effect,a new geometry structure of thin-disk crystal with anti-ASE cap and beveled edge is designed.