Dynamics of solid state coherent light sources

This book chapter aims at reviewing in brief the fundamentals of rare-earth-ion spectroscopy in dielectric solids, with special emphasis on energy-transfer upconversion between neighboring active ions in a solid-state host lattice. The energy-level scheme of the 4f sub-shell of rare-earth ions is explained and the main intra- and inter-ionic electronic transition processes are introduced. The pump-power dependence of upconversion luminescence and the influence of inhomogeneous active-ion distributions on energy-transfer upconversion are discussed. Examples illustrate how energy-transfer upconversion can impact the performance of solid-state lasers in a negative or positive manner