Thermal lensing and spherical aberration in high-power transversally pumped laser rods

A precise knowledge of the thermal effects in laser crystals is very important for high-power laser design, but some relevant parameters are most often neglected in their calculation. In this paper, with the example of transversally pumped, high-power Nd:YAG lasers, we show the importance of the thermal dependence of the gain medium's physical properties such as the thermal conductivity, the dn/dT and the expansion coefficient on the thermal aberration and thermal lensing values; we also prove that the choice of the resonator can influence the amount of spherical aberration. Finally, analytically calculated values are confronted to experimental values, and show a very good agreement.