Highly Efficient Cryogenically Cooled Ho: YLF Oscillator

High-energy sources operating at 2.1 μm are of interest in many applications such as LIDAR, material processing, and as pump sources for high-energy mid-IR non-linear conversion systems. Commonly used bulk laser materials for these applications are Ho:YLF and Ho:YAG and they typically operate at 2050–2122 nm. The average power and pulse energy scaling with overall efficiency in Ho:YLF remains limited at room temperature due to thermal effets. However, cryogenic cooling has been shown to reduce laser threshhold and improve thermo-optic and mechanical properties of YAG, enhancing the overall performance of Ho3+ in YAG and YLF. Cryogenically cooled pulsed laser operation in Ho:YLF was reported [1], despite the low threshold offered by cryogenic conditions, the overall laser efficiency was low due to biaxial crystal structure, requring polorised pump source at 1940 nm. Ho:YAg cryo laser with high average power scaling, exellent slope efficincy ~70 % and pulse energy operation have been successfully demonstrated [2]–[3].