Rotational quasienergy states and alignment of molecules in a strong laser field

The interaction of a molecule with a strong laser field is investigated. Raman-type transitions between rotational levels of a fixed vibrational state of the ground-state term are taken into account in the "quantum rotator" approximation. An initial problem of the evolution of the state of a molecule interacting with a pulsed field is solved. The dynamics of the degree of alignment of a molecule with respect to the direction of polarization of the field during the pulse is investigated. It is shown that for sufficiently long pulses with a smooth envelope the axis of the molecule adiabatically follows the time-varying field amplitude, and alignment is maximum when the field intensity is maximum. It is shown that alignment of molecules can be substantial only if the second-order composite matrix elements, determining the probability amplitudes of transitions between rotational levels of a molecule, are much greater than the dissociation broadening of the levels. The angular distribution of the dissociation products of a molecule in a strong laser field is investigated. (C) 1999 American Institute of Physics. [S1063-7761(99)00411-4].