Spectral and polarization hole burning in neodymium glass lasers

Gain saturation in short-pulse glass laser amplifiers is treated including both spectral and polarization hole burning. Site-to-site differences in energy levels, transition probabilities, and orientations of the lasing ion in glass result in a distribution of stimulated emission cross sections and selective deexcitation of subsets of ions by a laser beam. These spectroscopic inhomogeneities are described by simple models whose parameters include the average emission cross section, the ratio of homogeneous-to-inhomogeneous linewidths, and the polarized cross section ratio. Performance of amplifiers based on the model media is calculated. Values for parameters to model an actual laser glass are obtained from standard fluorescence measurements and from resonant fluorescence line-narrowing (FLN) experiments. The predicted gain of a Nd-doped laser glass (ED-2) is compared to published amplifier measurements. The good agreement obtained demonstrates that data from FLN experiments provide sufficient information to model the performance of a glass amplifier in the large-signal gain regime. The results can also be used to guide the selection of glasses for increased energy extraction efficiency. Optimization of laser performance by varying parameters through changes in the host glass composition is discussed.