Laser power, cell temperature, and beam quality dependence on cell length of static Cs DPAL

Abstract

The influence of cell length of a static diode-pumped Cs laser on laser power, gain medium temperature, and laser beam quality is studied theoretically using a 3D time-dependent computational fluid dynamics model where Gaussian spatial shapes of the pump and laser intensities in any cross section of the beams are assumed. Reasonable agreement with power measurements in a static diode-pumped alkali laser (DPAL) with 20 mm cell length [Electron. Lett.44, 582 (2008)ELLEAK0013-519410.1049/el:20080728] is obtained. It is shown that the gain medium temperature rise caused by the pump beam absorption can be decreased by increasing the length of the alkali cell and that, for given conditions, there is an optimal cell length corresponding to maximum laser power. At ∼100 W pump power the optimum cell length of ∼50−60 mm is larger than the 20 mm length usually used in DPAL experiments. The increase of the cell length from 20 to 60 mm results in decrease of the gain medium temperature rise by 100–150°K, making it possible to avoid degradation of the laser power due to chemical reactions in the gain medium. Laser beam quality in terms of Strehl ratio was calculated as a function of pump power and length of the DPAL cell and found to decrease as the DPAL cell length is increased. It is shown that the wavefront corrections result in substantial increase of the Strehl ratio and hence in improvement of the laser beam quality.