Experimental and numerical analysis of thermal lensing effects in Nd:YVO ₄

The power dependent wavefront distortions in a Nd:YVO₄ laser amplifier were analyzed using a 976 nm probe beam. The experimental results were in excellent agreement with a numerical thermo-optical model based on split-step Fourier propagation. Although direct pumping at 878.6 nm was used, the quantum defect was identified as the dominant heat source (99 % of total heat) while energy transfer upconversion and fluorescence quenching have only a local contribution. As a result, the thermal lens reached 14 dpt dioptric power at 43 W output power (46 % efficiency). Apart from the defocus, astigmatism and spherical aberrations were identified as main components of the thermal lens.