Theoretical Analysis On The Thermal Effects Of Laser Medium

High average power and high beam quality solid-state laser is one of the research focuses currently. Thermal effects is an important factor to restrict solid-state laser towards high average power and high beam quality. Therefore, study on thermal effects of laser medium has important theoretical significance and practical value. Thermal effects in rod laser medium and slab laser medium are analyzed and compared in detailed in this paper. The main contents are as followed:Firstly, analysis of thermal effects of side-pumped rod is presented. Through the analysis on the temperature distribution, stress distribution, the thermal induced depolarization and thermal lensing, we realized that inhomogeneous distribution of temperature is the origin of thermal effects. Matching between pumping source and absorption spectra of laser medium, optimum cooling mode and optical compensation are very important in reducing the thermal effects. Quantitative analysis on the relationship between pump power limit and radius and length of the rod is carried out.Secondly, heat resource, temperature distribution, stress distribution in end-pumped rod are analyzed. By calculation of optical path difference, the effective focal length of the thermal lensing is discussed. Temperature gradient, thermal stress and end constraint are factors causing thermal lensing. Among them, temperature gradient and thermal stress are the main factors in side-pumped rod. But in end-pumped rod, Temperature gradient and end constraint has a larger contribution to thermal lensing.Thirdly, temperature distribution and stress distribution in face-pumped slab laser medium are analyzed. Compared with rod medium, the highest temperature and the maximum of thermal stress in slab medium are lower, power capacity of the slab medium is higher. Then isotropic medium is taken as an example, thermal lensing of the slab is analyzed and compared with thermal lensing of rod. The results show that the thermal effects of slab laser medium are lower than rod.Finally, according to bi-directionally side-pumped slab medium, on the base of heat resource and heat transfer model, temperature distribution, stress distribution and thermal lensing are analyzed in theory. In comparison with thermal effects in face-pumped slab, it shows that when pumping efficiency is 1, they have some similarities in expression. Using finite element simulation software COMSOL, the maximum of each thermal stress components in laser medium Nd:YAG is numerically calculated and located accurately. The distribution of thermal stress components in laser medium are stimulated and analyzed clearly. The results of computer simulation are in concordance with the theoretical analysis.Through systematic study and analysis on thermal effects in rod and slab laser medium, the facts that thermal effects is serious and thermal effects is problem urgently to be solved are disclosed. The conclusions in this paper provide a reference for reducing the thermal effect, improving beam quality and out power.