Determination of orientation of the ground state using twohyphen;photon nonresonant excitation

摘要

A method is presented for determining the populationAlcub;0rcub;0+, the alignment factorsAlcub;2rcub;qplusmn;andAlcub;4rcub;qthinsp;plusmn;, and the orientation factorsAlcub;1rcub;qplusmn;and Alcub;3rcub;qplusmn;for a ground state distribution of diatomic (symmetric top) molecules probed by elliptically polarized twohyphen;photon nonresonant excitation. General expressions are developed for theO,P,Q,R, andSbranch transitions as a function of the rotational quantum number,J. This treatment assumes that the resonant state reached by the twohyphen;photon transition is subsequently detected independent of its orientation and alignment. This can be achieved by 2+nmultiphoton ionization in which the ionization steps are saturated, or by 2+1 laser induced fluorescence in which the fluorescence is collected independent of its polarization and spatial anisotropy. For the case where elliptically polarized light is created by passing linearly polarized light through a quarterhyphen;wave plate, the alignment and orientation moments can be independently determined using a single experimental excitationndash;detection geometry.