Objective Thin-disk lasers have become one of the main research targets in the high-power solid laser technology, owing to their short thermal conduction distance, which in turn causes a significant reduction in the thermal lensing effect. However, with the increase of pump caliber and pump power, the distorted wavefront caused by the increasingly serious thermal effect becomes one of the important factors restricting the output power and beam quality of laser. In this study, a new central radiative cooling structure is proposed. This structure satisfies the cooling requirements of thin-disk gain media and effectively reduces the thermal teratogenesis of gain media under a high-power loading. We hope that our basic strategy and findings can provide new approaches and ideas to achieve highly efficient cooling and distorted wavefront control of high-power thin-disk gain media.
Methods The thermal teratogenicity of a large thin-disk gain medium is considerably large. To overcome this drawback, the technical route of microchannel composite jet impingement based on nonuniform cooling was proposed. Based on the technical route, the design of the central radiative structure cooler was created. In the central region of the heat transfer, jet impingement reduced the thickness of the boundary layer to enhance heat transfer and reduce the central temperature and thermal teratogenicity of the gain medium through “peak-clipping”. The peripheral heat transfer runner was designed as a microchannel with a central radiative structure to guarantee the circumferential uniform distribution of flow field and realize the circumferential uniform cooling. Moreover, the effect of the different structure parameters on heat transfer performance and stress distortion in the gain medium was analyzed via the fluid-solid thermal coupling simulation. The performance comparison between the central radiative structure cooler and the microchannel cooler was completed through simulation and experiment.
Results and Discussions The performances of the central radiative structure cooler and the original microchannel cooler are compared through simulation and experiment, respectively. The simulation results reveal that the heat transfer performance of the central radiative structure cooler is slightly better than that of the conventional microchannel cooler. Moreover, the surface temperature distribution of the gain medium with the central radiative structure cooler exhibits better circumfluence uniformity (Fig. 7 and Fig. 10). The axial deformation of the extraction region of gain medium surface with the microchannel cooler is 4.3μm. Additionally, the deformation distribution is asymmetric, which makes it easy to generate high-order asymmetric aberrations (Fig. 10). The axial deformation of the extraction region of the gain medium surface with the central radiative structure cooler is 1.2μm, and the circumferential uniformity is found to be better (Fig. 7). The experimental results reveal that the wavefront distortion of gain medium with the original cooler reaches 3.27 λ under a full-power loading, whereas that of the gain medium with the central radiative structure cooler is reduced by more than 50% to 1.6λ (Fig. 12 and Fig. 13).
Conclusions Based on the idea of nonuniform cooling, the intensification of heat dissipation in the central region of the thin-disk gain medium can realize the effective control of thermally induced wavefront distortion. The cooler adopts the central radiative structure to realize the central symmetric distribution of temperature field and strain field of gain medium, avoid the generation of high-order asymmetric aberrations, and greatly reduce the difficulty in wavefront distortion correction of gain medium. The heat transfer performance of the microchannel cooler with a central radiative structure is slightly better than that of the conventional microchannel cooler. This can effectively reduce the peak temperature in the central high-temperature region of the cooled gain medium.
