Thermal lensing and depolarization in a highly pumped Nd:YAG laser amplifier

Abstract

Thermally induced lensing and depolarization by an Nd:YAG amplifier rod with a maximum pump power of 8 kW were measured. The beam waist position exhibited a nonlinear dependence on the pump power. From this, a linear relation between the refractive index change and pump power is derived, considering the propagation of the Gaussian probe beam in the laser rod with a quadratic index profile. The measured degree of polarization behind the laser rod confirms the thermal lens result that refractive index changes depend linearly on the pump power. Pumping above 5 kW leads to deviations of the refractive index distribution in the rod from radial symmetry.