Abstract
Results are presented of an interferometric investigation of the refractive index variations of K8 and L47 glasses and laser glasses under the action of neodymium laser radiation. Thermal instability, found in the laser glasses, is associated with the thermal excitation of the ions to the 4I11/2 level and with the existence of a nonradiative decay channel for the metastable level via the higher 2G9/2 level. The cross section of the 4F3/2→2G9/2 transition is determined.