Influence of collisions and pulse intensity on multiple photon absorption in SF6

Using a pyroelectric detector, the multiple photon absorption (MPA) of the SF₆ molecule in a wide range of pressures (10^-3 -1 torr) has been studied. The significant role of collisions in MPA has been shown. The fraction of molecules excited under essentially collisionless conditions has been defined. It is shown that under collisionless excitation of SF₆ (p < 10^-2 torr) at energy fluences E < 10^-1 J/cm² the intensity of the laser pulse plays the essential role, while in presence of collisions MPA is determined mainly by the energy fluence in the pulse.