Collisionless excitation of NH3 molecules via one- and two-photon transitions by multimode radiation of TEA CO2-laser

The excitation of ammonia by one- and two-photon transitions by TEA CO2-laser radiation has been studied under collisionless conditions. It has been shown that the experimental results of two-photon excitation of 14NH3 molecules in the 2v2a(1, 1) ← a(1, 1) transition by the 10P(24) CO2-laser line, the frequency offset of which is ≈ 0.02cm−1, can be described well by modelling the laser radiation as a broadband chaotic field. The experimental results of one-photon excitation in 14NH3 and 15NH3 [4], with the offset values exceeding the CO2-laser linewidth, can be also described well with the use of a chaotic field with a continuous spectrum. In the case of a nearly exact one-photon resonance, however, the excitation efficiency of molecules depends critically on the real mode structure of the CO2-laser radiation.