Dependence of Cs atoms density and laser power on gas velocity in Cs DPAL

The laser power dependence on gas velocity in flowing-gas diode pumped alkali lasers (DPALs) has been theoretically and experimentally studied, but the reasons for this dependence are not yet completely understood. Previously we reported on a flowing-gas Cs DPAL with separate temperature control of the laser cell and the alkali source, enabling continuous stable operation for more than one hour [Yacoby et al, Opt. Express 26, 17814 (2018)]. The dependence of the power on velocities of 1–4 m/s was monitored and it was found that for this range of velocities the power remains constant. In the present study the power at small flow velocities (<1 m/s) was investigated and found to decrease with decreasing velocity. The measurements were compared to a computational fluid dynamic model calculation. It was found that the main reason for the decrease in the output power is the strong dependence of the Cs density in the laser section on the gas velocity, whereas the gas heating due to the relaxation and quenching processes is much less important.