Two-pulse laser control for selective photofragment orientation

Abstract

The nuclear wave packet dynamics in the potential well of a bound molecule can be controlled by an intense infrared ͑IR͒-laser pulse. The phase of the nuclear wave packet motion is shown to depend on the phase of the laser field and the initial orientation of the molecule. We demonstrate, for diatomic heteronuclear molecules, that these spatial effects can be used to control the angular distribution of photofragments by selective dissociation of molecules with a given initial orientation from a sample of randomly oriented molecules.

Off-resonant vibrational excitation: Orientational dependence and spatial control of photofragments

“…The resonant case was discussed in detail in Ref. 8, and we found that molecules with opposite orientations will oscillate out of phase, as seen in Fig. 2͑b͒.…”

“…In the resonant case discussed in Ref. 8, we showed perfect agreement between the 1D and 3D model, and interpreted this as the absence of coupling between the rotational and vibrational motion, allowing us to represent the full 3D simulations as a sum over of independent 1D simulations. The resonant field only makes very small changes to the angular distribution, even if the intensity is increased to the same value as the off-resonant field, Iϭ10 12 W/cm 2 .…”

“…In the Appendix of Ref. 8, we derived an analytic expression ͑A15͒ for the WP motion in a harmonic potential. According to that expression, molecules which initially have opposite orientation will always oscillate out of phase.…”

“…We found that the phase of the WP oscillations depends on the initial orientation of the molecule or more precisely depends on the orientation of the permanent dipole moment in the electronic ground state: Two molecules initially with opposite orientation will oscillate out of phase. 8 One way to overcome the problem caused by initial isotropic orientation of molecules in an experiment will be to orient the sample of molecules prior to the application of the IR pulse. We propose in this paper an alternative scheme: Two IR laser pulses, one having a one-photon resonance with the vϭ0→vϭ1 transition, the other having a twophoton resonance with the same transition, are applied on a sample of randomly oriented molecules.…”

“…The computational models, which were presented in Ref. 8, are extended to include two IR laser pulses in Sec. II.…”