Far-infrared laser gain resulting from rotational perturbations

A simplified model is used to calculate the unsaturated gains of far-infrared rotational and vibrational-rotational laser transitions that are caused by rotational perturbations. Inversions are derived from the perturbation of an initial Boltzmann distribution of rotational populations, permitting the calculation of laser gains in terms of the perturbation parameters and the vibrational populations. The gain equations are applied to the three perturbations of H
2
O
¹⁶
that result in the largest number of laser lines. Numerical gain values in good qualitative agreement with experimental results are obtained.