Pulsed optoacoustic detection of multiple photon excitation in molecules

Abstract

Multiple photon excitation, saturation, and linear absorption of SF 6-argon mixtures when irradiated by a high power CO 2 TEA laser is investigated using a pulsed optoacoustic technique. At low intensities the expected linear dependence of the absorption on laser intensity is observed. At intermediate intensities the absorption exhibits a square root dependence on the incident laser intensity, a dependence which is typical for saturation of an inhomogeneously broadened absorption. At even higher intensities, the absorption shows an intensity dependence typical of multiple photon excitation. The laser intensity was varied between 0.016 kW/cm 2 and 5 MW/cm 2, values lower than that needed to produce multiple photon dissociation of SF 6. Increasing the collision frequency of the absorbing molecules with an inert buffer gas is observed to quench the multiple photon excitation.