The dynamics of collisionless infrared multiphoton absorption in S${\mathrm{F}}_6$ was studied using picosecond C${\mathrm{O}}_2$ laser pulses. It was found that at this new regime of light-matter interaction at very high laser intensities, the absorption in the quasicontinuum has a considerable intensity dependence. The deviation from an energy fluence scaling law was found to begin at about 200 MW/${\mathrm{cm}}^2$. Above this intensity, the multiphoton interaction between the laser and the molecule should be described by the full coherent Schrödinger equation rather than by the usual master rate equations. A novel method of preheating the S${\mathrm{F}}_6$ molecules is also described and the saturation behavior of these preheated molecules is measured with the picosecond pulses.

• Received 7 August 1980

DOI:https://doi.org/10.1103/PhysRevA.23.3094