Coherent optical control of molecular photodissociation

Absorption of a coherent superposition of a fundamental laser frequency phase-locked with one of its harmonics can induce complex interference effects between different pathways in atomic or molecular photo-processes, thereby permitting coherent optical control of chemical reactivity.

Large scale three-dimensional time-dependent wavepacket calculations for photodissociation of HD+ by an intense laser field with a phase locked superposition of the fundamental and second harmonic frequenies of a CO2 laser show large asymmetries in the fragment angular distributions. This effect can be used to induce almost 100% spatial separation of the isotopes.

The plot shows the angular distribution predicted for the H+ and D+ fragments after photodissociation of an initial HD+(v0,J0) rovibrational state for a specific relative phase of the fundamental and second harmonic. The angular distributions are closely peaked along the polarization axis of the laser, with essentially 100% of the H+ ions ejected in the forward direction and 100% of the D+ ions ejected in the backward direction. The separation effect is robust enought to survive experimental uncertainties in the intensities, phase, and variations in pulse-duration and distribution of initial rovibrational states of the HD+. This coherent control should thus persist even after averaging over realistic experimental conditions.

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