Thermal Lensing Effects in End pumped Er:YAG Laser

Abstract

The most difficult challenge in the design of such high-power end-pumped lasers is the handling of thermal problems that arise due to the high heat load in the small crystal volume. Most notably, the heat load leads to large temperature gradients both in the radial and axial directions referred to the pump beam axis. Such gradients may lead to severe thermal lensing effects due to the temperature dependence of the refractive index, and to large local stresses which induce a spatially varying birefringence and depolarization and may, in the worst event, lead to crystal fracture. The effects of thermal lensing and birefringence, and methods for compensation, are treated in following sections. The occurrence of thermal lensing may have serious implications on the stability conditions of the laser resonator, so it is necessary to take this into account in the resonator design.

Keywords: Er:YAG laser, high power end pumping, thermal lensing.