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 to Tsub(R) approx. equal to 40 K and Tsub(theta) approx. equal to 160 K in the free jet expansion from a pulsed supersonic nozzle has been investigated at energy fluences of 0.1 to 3.0 J x cm-2. For practically all laser lines which coincide with the linear absorption spectrum of the ν3 vibrational mode of SF6 [P(12)...P(28), 10,6 m], the dependence of the absorbed energy Esub(ab) on the exciting energy fluence was found to be steeper than linear Esub(ab) approx. equal to Oesup(n), where n = (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. (orig.)