Characterization of the heat loading of Nd-doped YAG, YOS, YLF, and GGG excited at diode pumping wavelengths

The parameter ξ (xi) is proposed as an alternative to the traditional solid-state laser media heating parameter, χ (chi). ξ is the ratio of heat produced to energy absorbed, and χ is the ratio of heat produced to the maximum stored energy in the upper laser level. The parameter ξ is particularly relevant to diode pumped systems. We demonstrate an experimental ξ characterization based on the determination of the steady state cooling rate (hence heating rate) of small sample crystals subjected to pump laser heating. Using measured fluorescent lifetimes of the samples and near zero doping (intrinsic) values, the doping independent (zero doping or zero quenching) parameters χφ and ξφ are determined. The results for all samples are in excellent agreement with calculations based solely on energy defect and nonradiative quenching of the upper level