Thermal analysis of side-pumped direct-liquid-cooled Nd: YAG thin-disk lasers

Thermal effects are the main obstacle for side-pumped direct-liquid-cooled Nd: YAG thin-disk lasers (SDNTDLs) to achieve high-power near-diffraction-limited laser output. A multiphysics model is established and several basic understandings are obtained. The temperature distribution of the disk under lateral non-uniform pumping shows that the total reflection transmission of the pump lights in the disk does not result in severe temperature fluctuations. The thickness of the thermal boundary layer is much less than half the thickness of the fluid, indicating that there is no thermal interaction between two adjacent disks. The component analysis of the thermally-induced wavefront aberration (TIWA) reveals that the influence of the fluid’s thermo-optic effect (TOE) which is awful in liquid lasers is not necessarily dominant in SDNTDLS due to the thin thermal boundary layer. When cooled by D2O, the wavefront aberration induced by the disk is much larger than that induced by the fluid. As a result, the TIWA exhibits a distribution of high at both sides and low at the center along the transverse direction of the disk, which is consistent with the experimental results. The wavefront aberration induced by the fluid’s TOE and that induced by the disk’s both TOE and deformation compensate for each other, indicating that the beam quality can be significantly improved by means of design optimization.