Modeling of high-pressure 12-micron NH3 lasers

Experimental measurements of small-signal gain in an optically-pumped NH3 amplifier are carried out at pressures ranging from 40 Torr to 760 Torr, and the results are used to validate a rate-equation model describing the amplifier dynamics. The gain measurements show that dilute mixtures of less than 0.5 percent NH3 in N2 are required to minimize the problems of gas heating due to pump absorption. The model is used to extrapolate the results to gas pressures of several atmospheres, and to demonstrate the potential for high-pressure operation of optically-pumped NH3 lasers.For a pump intensity of 100 MW/sq cm, calculations indicate that operation of an NH3 - N2 laser is feasible up to a pressure of 10 atm, which would provide a maximum continuous tuning range of 4/cm. High-resolution spectroscopy reveals that gain on a few NH3 transitions is eliminated at high pressures due to the presence of overlapping absorptions in other NH3 bands.