Modeling laser performance of scalable side pumped alkali laser

Diode pumped alkali lasers (DPAL) offer the potential for high power and efficient operation. The extremely low quantum defect of the alkali system minimizes thermal management requirements. At the same time DPALs keep advantages of gas lasers (no thermal stresses, high intrinsic beam quality). Side pumped geometry simplifies system design, separating laser and pump light and providing physical space for a large number of diode stacks needed for power scaling. The three-level nature of these lasers complicates modeling, making numerical simulation the most viable option for system studies in this geometry. We have built a simplified numerical code for simulation of CW laser performance in different side pumped geometries and studied performance of a rubidium DPAL with helium and methane buffer gases at high pump power. We observed dramatic differences in pump absorption with the laser turned off compared to an operating laser. Cell temperature is a key parameter that controls effective absorption length. If pump density is sufficiently high, we can find an operating point with optical to optical efficiency above 60% with reasonably homogenous spatial laser output profile even for a single side pumped laser cell.