Scaling up and controlling beam quality of flowing-gas diode pumped potassium laser with different pumping geometries: 3D CFD modeling

Comprehensive analysis of the performance and beam quality of subsonic flowing-gas K diode-pumped alkali lasers (DPALs) with different pumping geometries, using 3D computational fluid dynamics model, is reported. The model is first applied to a K DPAL with transverse pumping and parameters similar to those of the 1.5 kW K DPAL [Pitz et al, Proc. SPIE 9729, 972902 (2016)] and the calculated results are in satisfactory agreement with the measurements. To study the possibility of scaling up the K DPAL the model is then applied to 100-kW class device with transverse and end pumping geometry. Dependence of the output power on the flow velocity and the pumping geometry is studied. Comparison between end and transverse pumping schemes shows that the output power is almost unaffected by the pumping geometry. However, the spatial intensity distribution of the output laser beam depends on the pumping geometry: it is uniform for the end pumping, whereas for the transverse pumping it is strongly non-uniform at high gas temperature (corresponding to large density of K atoms), becoming more uniform with temperature reduction. The model is applied to evaluation of the beam quality of flowing-gas K DPALs which strongly depends on the refractive index distribution in the gain medium. The beam divergence and the width of the intensity profile in the far field for the end pumping appear to be much smaller than for the transverse pumping. Wave front corrections of the transversely pumped device using cylindrical lens results in substantial reduction of the laser beam divergence and improvement of its quality which becomes comparable with that of the end pumped laser.