The effect of mid-infrared and far-infrared emission, generated at NH3 excitation by intense radiation of a TEA CO2 laser, on ammonia absorption

Abstract

The effect of Mid-InfraRed (MIR) (λ ≅ 12 μm) and Far-InfraRed (FIR) (λ ≽ 100 μm) emission from excited ammonia on the absorption of intense radiation of a TEA CO2 laser has been studied experimentally under collisional and collisionless excitation conditions with ammonia pressures from 0.5 to 0.03 Torr. The energy of MIR and FIR emission was studied as a function of NH3 pressure and laser energy fluence. Particular emphasis was given to the kinetics of MIR and FIR emission generation at different NH3 pressures and to the measurement of the time delay of re-emitted pulses relative to the exciting CO2 laser pulse. It has been found that the re-emission in the MIR range is highly collisional in nature. The intensity of MIR emission drops sharply (asp3) with decreasing NH3 pressure and its delay time relative to the exciting laser pulse increases. At the same time, re-emission in the FIR range (in the case of resonant excitation of NH3 at the 9R (30) line of CO2 laser) is observed during an exciting pulse up top < 0.03 Torr. When binding the rotational sub-levels of a molecule with transitions, FIR emission acts as rotational relaxation and thus leads to an increase in NH3 IR absorption even at collisionless excitation.