Exploiting the natural doping gradient of Nd:YLF crystals for high-power end pumped lasers

Abstract

Of the various Neodymium-doped materials, Nd:YLF is particularly attractive for use in high-power diode endpumped solid-state lasers due to its weak thermal lens, especially on the σ-polarisation, and it’s long upper laser level lifetime that enables efficient energy storage for Q-switching. However, due to the low thermal fracture limit in Nd:YLF, power scaling has proven to be difficult. The researchers experienced fracture at 5 kHz. In order to address the fracture problem researchers decided to use crystals of a doping concentration below the 0.5% previously used. In addition, researchers decided to exploit the natural doping gradient along the length of the boule, which is especially pronounced at low concentrations but commonly ignored. In collaboration, VLOC estimated the doping gradient of a specially manufactured boule (Fig. 2) and maintained the crystal orientation information during the manufacturing process of the 45 mm long, 6 mm diameter crystals. Initial thermal calculations indicate that for these crystals, the lower-doping end can be pumped 58% harder than the higherdoping end before the thermal fracture limit is reached