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Composite thermally-induced focusing of a probe beam with Gaussian-distribution propagating through a cesium cell end-pumped by a LD

Diode-pumped alkali lasers (DPALs) have been developed in the recent years for their high Stocks efficiency, good beam quality, compact size and near-infrared emission wavelengths. Dividing a cylindrical vapor cell into many cylindrical annuli, we first obtain parameters such as the population density distributions, transition rates of pump photon absorption, and transition rates of laser photon emission of every annulus by use of a mathematical algorithm combining the procedures of heat transfer and laser kinetics together. After exploring the radial temperature distribution at the transverse section of a cesium vapor cell, we acquire the refractive index n and the thermal-optic coefficient dn/dT of each cylindrical annulus when the cesium vapor cell is end-pumped by a LD module. And then, we undertake a ray-trace theme to investigate the propagation of the incident beam with a perfect Gaussian distribution inside the vapor cell. By adopting the algorithm based on the complex self-consistency analyses in lens-like media, the intensity distributions of the probe beam outputted from an enclosed cesium vapor cell have been systematically evaluated for different pump powers. It has been seen that the intensity distributions of a Gaussian-distribution probe beam are different from those of a probe beam with flat-top-distribution. Finally, we get the effective focal length of a thermally-induced lens in each cylindrical annulus for different pumped-powers. It is obvious that the thermally-induced focusing phenomena for a Gaussian-distribution probe beam are much more serious than those for a flat-top distribution probe beam. These results will be helpful to improve the beam quality of a high-powered DPAL.