THE EFFECT OF THERMALLY-INDUCED GAIN GRADIENTS IN SOLID-STATE LASERS

A dependence of the small-signal gain in solid state lasers on the thermal loading is calculated. An average thermal power dependent gain reduction factor, eta(g)(Q), is defined in terms of the temperature coefficients of the laser gain curve, and the thermal conductivity of the laser rod. eta(g)(Q) arises from the shifts in the laser gain curve associated with the temperature gradients caused by optical pumping, and reduces the small-signal gain. The calculation of eta(g)(Q) for the specific cases of Nd:YAG and Nd:Cr:GSGG lasers indicates a reduction in the small-signal gain, from this mechanism alone, of 20-30% at high average power (200 W-cm-3, thermal).