The characteristics of multiple-photon absorption of SF6 molecules cooled in free jet expansion from a pulsed supersonic nozzle

The multiple-photon absorption of pulsed TEA CO₂ laser radiation by SF₆ molecules cooled toT_R40K andT_v160K in the free jet expansion from a pulsed supersonic nozzle has been investigated at energy fluences of 0.1 to 3.0 J·cm^–2.For practically all laser lines which coincide with the linear absorption spectrum of thev₃ vibrational mode of SF₆ [P(12)...P(28), 10,6 m], the dependence of the absorbed energyE_ab on the exciting energy fluence was found to be steeper than linearE_abⁿ, wheren=(1.1 to 1.8). Considerable increases of the absorption cross sections with increasing energy fluence were observed.The fraction of the molecules interacting with the laser radiation is estimated.