Experimental and numerical investigation of thermal effects in end-pumped Cr4+:forsterite lasers near room temperature

The results of a study which employs both experimental and theoretical methods to investigate the role of thermal effects in room-temperature Cr⁴⁺:forsterite lasers are presented. A novel model was developed to calculate the incident threshold pump power required to attain oscillation by taking into account absorption saturation and pump-induced thermal loading in the gain medium. Experimentally, the incident threshold pump power was measured as a function of the crystal boundary temperature for three Cr⁴⁺:forsterite laser crystals with different small-signal differential absorption coefficients α_p0 and/or cross-sectional areas. Excellent agreement was obtained between theory and experiment for values of the stimulated emission cross section comparable to those from previously reported data. The model was then used to numerically determine the optimum value of α_p0 which minimizes the incident threshold pump power in room-temperature Cr ⁴⁺:forsterite lasers. At a crystal boundary temperature of 15°C, the optimum value of α_p0 was determined to be 0.64 cm^-1 for a 2-cm-long Cr⁴⁺:forsterite crystal, corresponding to an unsaturated absorption of 72%. The use of crystals with an optimum absorption coefficient should lead to the realization of highly efficient CW Cr⁴⁺:forsterite lasers at room temperature