Thermal effects induced by hydraulic entrance in liquid direct cooled thin disk laser

In the Nd: YAG thin disk laser system, there is a hydraulic entrance distance when the fluid flows through the gain medium. By using the Ansys simulation software, the influence of the different hydraulic entrance distances on the heat transfer coefficient of the fluid was discussed. The influence of the hydraulic entrance distance on the thermal stress and the beam transmission was analyzed. The cooling effect of different coolant is simulated. When the fluid was in different flow state, the relationship between the hydraulic entrance distance and the heat transfer coefficient of the fluid was studied, while the relationship between the hydraulic entrance distance and the temperature of the medium was also studied. The range of the optimal hydraulic entrance distance was obtained in the high power laser cooling system. The results show that when the fluid flows through the gain medium, the different hydraulic entrance distance only moves the heat transfer coefficient curve of the fluid regularly. Therefore, it can realize small temperature gradient in the medium, while reducing the thermal stress as well as the wavefront distortion by avoiding the distance region (0-2.25 mm) where the heat transfer coefficient curve changes greatly, and finally, achieve a better cooling effect.