Two-level model for near saturated fluorescence in diatomic molecules

Abstract

The near saturated behavior of diatomic molecules is modeled by considering the interactions of two sets of rotational levels. The molecules are assumed to be subjected to high intensity laser radiation tuned to one particular rotational transition between the sets of levels. Previous two-level models for atomic fluorescence are modified to account for the strong coupling of rotational energy levels in molecules. The steadystate rate equations for the system are manipulated to give a simple expression for the total fluorescence power in terms of the electronic quenching rate Q(21), the spontaneous emission rate A(21), the stimulated emission rate B(21)I(21), and the population fractions of the lower and upper levels which are directly excited by the laser, F(l)(e) and F(2) (e), respectively. When the ratio of the rotational relaxation rates Q(22) and Q(ll) to Q(21) is on the order of 100 or less, the distribution of molecules amg rotational levels is found to be markedly non- Boltzmann. The influence of the non-Boltzmann distribution on data interpretation is discussed.