This thesis compiles recent achievements in optical refrigeration, cooling a 5 wt. % ytterbium doped yttrium lithium fluoride (Yb+3:YLF) crystal through anti-Stokes fluorescence to a new record low temperature. This is the coldest temperature to date, without the use of cryogens or mechanical refrigerators, and is achieved by taking advantage of the Stark manifold resonance and high doping concentration available in a crystalline host. Cooling to \u223c155K from room temperature in a single stage with a cooling power of 90mW has been achieved, outperforming multi-stage Peltier coolers. Further cooling below the NIST-defined cryogenic temperature of 123K is shown feasible for for this record cooling sample given sufficient absorbed power. With an order of magnitude improvement to parasitic background absorption, theory predicts cooling which approaches liquid nitrogen temperatures. With this accomplishment, a new realm of possibilities toward an all solid-state optical cryocooler is within reach.
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