A 16-µm radiation source utilizing four-wave mixing in cooled parahydrogen gas

Improvements in a 16-μm radiation source based upon the combined effects of stimulated rotational Raman scattering and resonantly enhanced four-wave mixing in parahydrogen gas are described. For this source, the input waves of which are provided by temporally and spatially coincident pulsed beams from a ruby and CO
2
TEA laser, it was found that cooling the parahydrogen gas from 300 K to <100 K, at constant molecular density, increased the output at 16 μm by roughly a factor 4. The maximum output was measured to be
\sim 40 \mu
J/pulse, which is near the theoretical limit for the 2.5 MW CO
2
laser intensities that were applied.