Theoretical assessment of a high power continuous-wave 4-level solid laser

The performance of a steady-state continuous-wave 4-level laser is analysed on the basis of a simplified model in which conditions are assumed to be uniform throughout the laser. It is shown that the model remains a close approximation to this assumption for reflectivities greater than 50% and it is further shown that this includes the region of practical interest. Within this region the laser power output is proportional to length (for uniform pumping and optimized mirror reflectance) and decreases rapidly as host losses increase. The upper and lower limits to the input power density, set respectively by the thermomechanical properties of the host material and the minimum threshold power requirement, are defined for a cylindrical laser rod. It is shown that there is a maximum value of laser cross-sectional area for which continuous-wave operation is possible and which is inversely proportional to the host loss coefficient. Calculations performed for Nd 3+ : glass show that this material is theoretically capable of producing some tens of watts continuous-wave power.