Thermal modeling of solid nonfocusing pump-light collectors used for diode-pumped Nd:YAG lasers

We have developed a thermal model for the determination of the temperature distribution of a diode side-pumped Nd:YAG laser in which the laser rod is fixed in a solid nonfocusing (prismatic) pump-light collector. The model permits the temperature to be determined as a function of both spatial and temporal parameters for a wide range of boundary conditions and different collector materials. Interferometric measurements were carried out to obtain the averaged rod temperatures for comparison with results from the model and to fix a convective-cooling rate for ambient air that best fits the experimental results. Two cases were studied both theoretically and experimentally with artificial sapphire and BK7 as prism materials, and good agreement was achieved between model and experimental results. The use of artificial sapphire as the prism material reduces by a factor of ~7 both the rod temperature and the warm-up time compared with BK7 glass. Peltier cooling of the underside of the BK7 glass prism yields thermal characteristics of the device that are similar to those devices with sapphire prisms. Calculations also show that the thermal properties of the fixant are not critical for moderate fixant thermal diffusivities (i.e., κ_f > 10⁻⁸–10⁻⁷ m² s⁻¹), thus the choice of an appropriate fixant can be based on its mechanical and index-matching properties alone.