The role of helium in the H2O laser

The addition of helium increases the output of both pulsed and CW H
2
O lasers. Spectroscopic time-varying gas temperature measurements in pulsed H
2
lasers show that the gas temperature rise of ∼1600 K in "pure" H
2
O is reduced to only ∼200 K when helium is added. Evidence is presented, indicating that the increase in output when helium is added is primarily due to gas cooling.