Coherent anti-Stokes Raman scattering measurements of N_2(X, v) at low pressures corrected for stimulated Raman scattering

Abstract

Number density measurements of the populations of the vibrational states of the electronic ground state of molecules that use scanning coherent anti-Stokes Raman scattering (CARS) spectroscopy at pressures in which Doppler broadening dominates can be strongly influenced by population changes caused by the stimulated Raman process. Such measurements have been carried out in heterogeneous deactivation studies of vibrationally excited N(2) on various solid surfaces at 17 Torr. This process perturbs the populations of the states connected by the incident fields. It typically reduces the population difference and therefore reduces the observed CARS signal. Thus, as the incident laser irradiance increases, the observed signal exhibits saturation. A linear relationship for this effect in terms of the average laser powers is derived, providing a scheme for calibrating the initial onset of this saturation process. This calibration method permits simple corrections of the CARS data for saturation.