Nonlinear absorption and generation of microwave radiation due to interaction of ammonia molecules with high-power infrared radiation

An investigation was made of the excitation of ¹⁴NH₃ molecules at pressures of 10^–2–1 Torr by CO₂ laser pulses in a wide range of laser radiation energy densities (Φ=10^–3–10 J/cm²) and of offsets of the laser frequency from the absorption lines of the vibrational–rotational transition in the ν₂ band of ammonia. Effective excitation of ammonia as a result of nonresonant interaction with infrared radiation was due to field broadening. Calculations dispensing with fitting parameters accounted for the experimental results (within the limits of the measurement error). The anomalously strong absorption of ammonia due to resonant pumping was attributed to generation of high-intensity microwave radiation which suppressed the rotational bottleneck in the excitation of molecules.