Energy relaxation time in a gas mixture measured by a photothermal probe beam deflection technique

The deflection of a cw probe laser beam, which occurs in a gas mixture after the absorption of a short laser pump pulse, was experimentally studied inside the irradiated region in order to characterize the generation of photothermal and photoacoustic effects. The time varying component of the probe deflection was detected, and the results are presented as functions of pumping fluences, laser wavelengths and gas pressures. Numerical modelling of the thermo-acoustic dynamics leads to the definition of an effective energy relaxation time for SF₆/Ar gas mixtures. An interesting nonlinear behaviour of this energy relaxation time is reported.