Optical refrigeration of Tm:YLF and Ho:YLF crystals

We report the first observation of laser cooling in 1% doped Tm: YLF by 0.5 K and in 0.8% doped Ho: YLF crystals by 0.1 K starting from room temperature in air. To achieve this, we designed and constructed a high power, broadly tunable (1735 nm-2086 nm) continuous wave singly-resonant optical parametric oscillator. (OPO). The cooling experiments were performed at ambient pressure, and temperature changes were measured using a thermal camera.