Collisional relaxation in resonantly pumped14NH3inversion systems

Abstract

The recent experiments of Steward and Parsons (1983) on the absorption spectrum of the resonantly pumped (J,K)=(3,3) inversion transition in 14NH3 have been repeated at lower pressures and using a more sensitive detection technique. In both studies, amplification of the probe radiation field under certain pump and probe field conditions predicted by Mollow (1972) has been observed. The theoretical model of Steward and Parsons predicts fine structure on spectra that are otherwise qualitatively the same as those predicted by Mollow, but their experimental results were inconclusive in deciding on the presence, or otherwise, of this structure. Such fine structure is not observed. A theoretical model, incorporating a full master equation approach, is developed to calculate the absorption spectrum of a simplified, resonantly pumped, degenerate system based on the (J,K)=(3,3) inversion system. Several different collisional relaxation models are used. For this system, an isotropic collision process cannot change the component of the total angular momentum of a molecule on a space-fixed axis. In agreement with the experimental results, both isotropic and non-isotropic collisional relaxation models produce spectra that do not show any of the fine structure predicted by Steward and Parsons, Also, all the collision models produce spectra that agree closely with each other showing that, for the energy level scheme considered, the spectra resulting from the theoretical model used are insensitive to collisional selection rules.