7B7 - Output spectra of Nd : YAG and ruby lasers and implications for laser linewidth determining mechanisms

The results of a number of experiments dealing with the output spectra of Nd: YAG and ruby lasers are presented. The aim of these experiments is to determine and clarify, at least qualitatively, the mechanisms responsible for the observed overall linewidths of Nd : YAG lasers. Two such mechanisms which may be expected to be present in solid-state lasers are inhomogeneous broadening of the fluorescent line, and slow spatial relaxation. In general, the experiments have indicated that the situation in Nd: YAG is considerably less clear-cut than in ruby. Thus, in ruby the inhomogeneously broadened linewidth is quite narrow and, therefore, plays essentially no role in determining the linewidth of ruby laser output spectra. Instead, the overall linewidth seems to be determined entirely by effects caused by slow spatial relaxation. In Nd : YAG, depending on the particular rod, the laser linewidth can be determined by inhomogeneous broadening, spatial relaxation effects, or a combination of the two. Indications are that spatial relaxation is faster in Nd: YAG than in ruby. However, in good quality Nd: YAG rods, slow spatial relaxation still seems to play a dominant role.