Buffer gases to increase the efficiency of an optically pumped far infrared D2O laser

The effects of buffer gas additives on the performance of an optically pumped D
2
O laser operating at 385 μm have been investigated both experimentally and by numerical simulation. Three gases, sulphur hexafluoride, carbon tetrafluoride, and
n
-hexane, were found to produce an increase of up to 40 percent in the pumping efficiency, as well as significant lengthening of the far infrared pulse. Under optimum conditions, 2.6 J in a 1 μs long pulse have been obtained. The buffer gases are shown to eliminate the vibrational deexcitation bottleneck, which in pure D
2
O leads to an accumulation of population in the upper vibrational leve and, hence, a reduction in the efficiency of absorption of the pump beam. Comparison of the observed buffer gas effects with the predictions of a numerical simulation code based on a rate equation model gives information about the constants for vibrational and rotational relaxation rates due to D
2
O-D
2
O and D
2
O-buffer gas collisions.