Depolarization of the exit beam of a neodymium-glass amplifier in the case of small-scale self-focusing

An experimental investigation was made of a nonlinear increase in the degree of depolarization of an initially linearly polarized high-power laser beam propagating through a four-stage rod amplifier made of neodymium-doped phosphate glass. This increase was found to be due to small-scale self-focusing of the beam. The effect could be used to monitor self-focusing in high-power amplifiers.