A new generation of solid-state lasers

A discussion is presented of recent advances in research and development relating to highefficiency lasers made from activated ionic crystals (specifically, gadolinium-scandium-gallium garnet activated by Nd$^{3+}$ and Cr$^{3+}$ and yttrium aluminum garnet activated by Er$^{3+}$) and multicomponent glasses activated by Nd$^{3+}$, Er$^{3+}$ and Yb$^{3+}$, along with tunable color-center lasers made from lithium fluoride. The physical processes, which occur in these active crystals and which lead to enhanced population inversion associated with the laser transition, are discussed, including energy transfer from sensitizer ions to active ions and cross-relaxation between the level systems of neighboring active ions. Processes that give rise to increased efficiency in tunable color-center lasers based on LiF crystals are analyzed; also mentioned is work relating to the fabrication of passive Q switches using LiF crystals with F$_2^-$ color centers.