The fluorescence of a molecular gas excited a strong monochromatic standing wave radiation field

Abstract

Among the different methods of nonlinear spectrosccpy the method of analysing the fluorescence light is useful in investigating weak absorbing molecular transitions. In this paper the fluorescence of a molecular gas in the resonator of a high-power single mode laser is investigated. By tuning the standing wave field frequency to centre of the absorption line one observes a narrow local minimum for the fluorescence. This minimum is determined by the homogeneously broadened line of the molecular transition and gives information of the different molecular relaxation processes. The influence of vibrational-rotational relaxations, velocity changing collisions and spatial inhomogeneous distribution of the population caused by the standing wave field on the width and contrast of the minimum is theoretically investigated. It will be shown, that vibrational-rotational and velocity changing collisions increase the intensity of the fluorescence. The spatial inhomogeneous distribution of population caused by the excitation decreases the contrast.