Laser cooling of a solid from ambient temperature

A 250 mum diameter fibre of ytterbium-doped ZBLAN was cooled by 13 K from r oom temperature. The cooling was performed in vacuum to limit the thermal l oad on the fibre. 0.85 W of laser light at 1015 nm was coupled into the fib re. The ytterbium ions absorbed this light, and the excited atoms thermaliz ed phononically and on average emitted light at a wavelength of 996 nm. Sin ce the quantum efficiency of the transition was high, this resulted in a ne t loss of energy from the glass, producing net bulk cooling.