Quantum control via the dynamic Stark effect: Application to switched rotational wave packets and molecular axis alignment

Nonperturbative quantum control schemes in the intermediate field strength (nonionizing) regime are investigated. We restrict the matter-field interaction to the nonresonant dynamic Stark effect (NRDSE) as induced by infrared laser fields, which we argue is a new and general tool for quantum control of atomic and molecular dynamics. For the case of Raman coupled matter states, an effective Hamiltionian may be constructed, and quantum control via NRDSE may be thought of as reversibly modifying the effective Hamiltonian during system propagation, thus leading to control over dynamic processes. As an illustration, the creation of field-free switched wave packets through the adiabatic turn on and sudden turn off of the NRDSE is considered and experimentally demonstrated. Wave packets generated through the switched NRDSE interaction may be very different in form and content than wave packets generated via resonant transitions with Gaussian optical pulses. In order to provide an example, we discuss the specific case of rotational wave packet dynamics where the NRDSE manifests itself as molecular axis alignment. This technique is applied to the creation of field-free molecular axis alignment using an intense switched 1.064 mu m laser pulse. This switched laser pulse was generated via a plasma shuttering technique, giving a pulse with a rise time of 150 ps and a fall time of 170 fs. The temporal evolution of the molecular axis alignment is probed via the optical Kerr effect. Field-free alignment via the switched NRDSE is demonstrated for both linear (CO2, CS2) and symmetric top (1,2-propadiene) polyatomic molecules.