Jianli Shang

Analytical approach to thermal lensing in end-pumped Yb:YAG thin-disk laser

Thermal lensing in the thin-disk laser influences the output beam quality and optical efficiency significantly. In this paper, an analytical approach is taken to study the production mechanisms, features, and influences of thermal lensing in the end-pumped thin-disk laser. We calculate the distributions of temperature, stress, strain, and expansion in the disk and the curvature of the crystal using an analytic method. The expressions of the thermal lens focal length depending on the radius are presented. The optical path difference, a major cause of thermal lensing, is induced by the thermo-optical effect, the photoelastic effect, and inhomogeneous distribution of thermal expansion and the excited population. Thermal lensing is found to be aspheric with undesired aberrations and birefringence effects. Furthermore, a convex mirror due to the axial temperature gradient occurs in a free disk, and the convex mirror is found to be spherical in the center region of the disk. Based on the results of our analysis, the aspect ratio and size of the laser mode of the gain region may be adjusted to limit the damaging effects of thermal lensing.

Modeling of end-pumped Yb:YAG thin-disk lasers with nonuniform temperature distribution

A plane wave model with nonuniform temperature distribution in the thin-disk crystal is developed to describe the dynamic behavior of an end-pumped Yb:YAG thin-disk laser. A set of couple-rate equations and 2D stationary heat-conduction equations are derived. The stable temperature distribution in the disk crystal is calculated using a numerical iterative method. The analytic expression is capable of dealing with more practical laser systems than previous works on this subject as it allows for nonuniform temperature distribution in the disk crystal. Based on these results, we examined laser output intensity as a function of pump intensity, dopant concentration, resonator coupler reflectivity, crystal thickness and temperature of cooling liquid.

Optical model and optimal output coupler for a continuous wave Yb:YAG thin-disk laser with multiple-disk configuration

This article presents the fundamental principles of operational performance of a continuous wave (cw) thin-disk laser with multiple disks in one resonator. Based on the model of an end-pumped Yb:YAG thin-disk laser with nonuniform temperature distribution, the effect of the multiple disks in one resonator is considered. The analytic expressions are derived to analyze the laser output intensity, laser intensity in the resonator, threshold intensity, and the optical efficiency of a thin-disk laser with multiple disks arranged in series. The dependence of output coupler reflectivity and the number of thin disks on various parameters are investigated, which are useful to determine the optimal output coupler reflectivity of the thin-disk lasers and control the laser intensity in the resonator.