Knowledge Bank

Resonant absorption of energy from an intense laser pulse and its distribution in high vibrational states of the absorbing molecules have been studied in the regime where V-V collisions populate high-lying vibrationa1 states. The model assumes that the pulse duration $Tp\gg Tvv,Tvt\gg Tp$, and that the pulse equalized $n0$ and $n1,nv$, being the population of $|v>$. The number of absorbed quanta/mol. is then calculated to be $(1-n1)2$, with $1/n12+4(1n 2n1)=4+Tp/Tvv$. To test the theory, the absorption of a 0.1J 2-4 $\mu$sec P(32) $CO2$ laser pulse by the $\nu 3(v=0\to 1)$ fundamental of $CH3F$ is being studied. The observed absorption of 2-3 quanta/mol. implies $Tvv\sim 1 \mu$sec-Torr, Evidence that all energy goes into vibrations has been obtained by measuring the vibrational temperature $(Tv)$ using a new laser-induced fluorescence technique. Measurements show $Tv\simeq 2000\circ K$, in good agreement with model.