Optical refrigeration to 119 K, below National Institute of Standards and Technology cryogenic temperature

We report on bulk optical refrigeration of Yb:YLF crystal to a temperature of ∼124 K, starting from the ambient. This is achieved by pumping the E4-E5 Stark multiplet transition at ∼1020 nm. A lower temperature of 119 1 K ( ∼ − 154C) with available cooling power of 18 mW is attained when the temperature of the surrounding crystal is reduced to 210 K. This result is within only a few degrees of the minimum achievable temperature of our crystal and signifies the bulk solid-state laser cooling below the National Institute of Standards and Technology (NIST)