Modeling of Flowing-Gas Diode-Pumped Potassium Laser with Different Pumping Geometries: Scaling Up and Controlling Beam Quality

Comprehensive analysis of the performance and beam quality of flowing-gas K diode-pumped alkali lasers (DPALs) with different pumping geometries, using 3-D computational fluid dynamics model, is presented. Recently, flowing-gas K DPAL with an output power of ∼2 kW was reported and there is interest in developing multi-kilowatt DPALs. To study the possibility of scaling up the K DPAL, the model is 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 to an optimal value below which the output power begins to fall. The model is applied to the 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 result in substantial reduction of the laser beam divergence and improvement of its quality, which becomes comparable with that of the end pumped laser.