Abstract

High energy laser sources operating around 2 µm are of interest in variety of applications: LIDAR, material processing, medicine and pump sources for optical parametric oscillators (OPOs) for high-energy mid-IR nonlinear conversion. 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 limitations. Cryogenic cooling of Ho:YAG or Ho:YLF offers vast improvements in thermo-optical and thermo-mechanical properties of quasi three level gain media, but only moderate average powers and pulsed energies are achieved [1-3]. One of the key benefits from cryogenic cooling comes from the reduction of the thermal population of the lower lasing level, resulting in a four-level like behaviour. This significantly reduces the pump power required to achieve transparency and allows for much larger mode volumes to be used when compared to room-temperature operation of such lasers [4-5]. The high energy scaling with high repetition rate of the cryogenic or room temperature of Ho³⁺ in YAG/YLF host is yet to be demonstrated.

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