High Energy Cryogenically Cooled Ho:YAG Oscillator

High energy laser sources operating around 2 µm are of interest in a variety of applications: LIDAR, material processing, medicine and pump sources for optical parametric oscillators (OPOs) for high-energy mid-IR nonlinear conversion. The OPO approach using ZGP is a scalable route for generating mid-IR radiation. In order to achieve high energy output, a pump source with wavelengths above 2.05 µm and excellent beam quality is required. Different laser configurations using Ho:YLF and Ho:YAG at room temperature have been used, but with thermal issues such as thermo-optical and mechanical properties being the major limitations. Cryogenic cooling results in drastic improvements in the thermos-optical and mechanical properties of YLF and YAG. Additionally, changes in the holmium ion population distribution creates a near four-level material, enabling larger mode volumes to be pumped and a significant reduction of the laser threshold in comparison to room temperature operation [1] , [2] . The value of cryogenic cooling was demonstrated as early as the 1980s, where Ho 3+ in YAG and YLF flash-pumped in co-doped scenario were reported [3] , [4] . High energy resonantly pumped Ho:YLF operating at cryogenic temperatures were reported by H. Fonnum et. al [5] , with <1 W average power.