JOURNAL DE PHYSIQUE IV Colloque C4, suppl6ment au Journal de Physique 111, Volume 4, avril1994 Pulsed photoacoustic study of collisional effects in IR multiphoton absorption measurements

The pulsed laser photoacoustic technique, simultaneously used with transmission spectroscopy, was applied for detailed study of IR multiphoton absorption processes in polyatomic molecules. Collisional effects were specially investigated in SF, diluted with Ar as nonabsorbing species. The results regarding the enhanced absorption cross sections (0") for SF,-Ar mixtures are obtained with precision of +18- S 9 %. The differential absorption cross sections (o:), as well as the average number of absorbed photons <n> per SF, molecule in 0, I- 0,7 J/cm2 fluence range and 1- 140 mbar Ar pressure range are also presented. Background Information The effects of the buffer gas on multiphoton absorption (MPA) in SF, have been in the past [I] and recently very thoroughly studied [2, 31 mainly by transmission spectroscopy techniques (TRS). The important characteristics of MPA processes have been determined as: absorption cross sections (oe) and differential absorption cross sections (0:) rotational and translational temperatures, etc. under the collisions of the different buffer gases, but primarily in details in the time scale adequate to laser pulse duration time [2, 31. The aim of this contribution is to present the MPA data obtained by application o