Photonics Research, 2019, 7 (4): 04000445, Published Online: Apr. 11, 2019
Observation of optical refrigeration in a holmium-doped crystal
Abstract
We report, to the best of our knowledge, the first demonstration of solid-state optical refrigeration of a Ho-doped material. A 1 mol% Ho-doped yttrium lithium fluoride (YLF) crystal is cooled by mid-IR laser radiation, and its external quantum efficiency and parasitic background absorption are evaluated. Using detailed temperature-dependent spectroscopic analysis, the minimum achievable temperature of a 1% Ho:YLF sample is estimated. Owing to its narrower ground- and excited-state manifolds, larger absorption cross section, and the coincidence of the optimum cooling wavelength of 2070 nm with commercially available high-power and highly efficient Tm-fiber lasers, Ho3+-doped crystals are superior to Tm3+-doped systems for mid-IR optical refrigeration. With further improvement in material purity and increased doping concentration, they offer great potential towards enhancing the cooling efficiency nearly two-fold over the best current Yb:YLF systems, achieving lower temperatures as well as for the realization of eye-safe mid-IR high-power radiation balanced lasers.
Saeid Rostami, Alexander R. Albrecht, Azzurra Volpi, Mansoor Sheik-Bahae. Observation of optical refrigeration in a holmium-doped crystal[J]. Photonics Research, 2019, 7(4): 04000445.