Impulsive orientation and alignment of quantum-state-selected NO molecules

Abstract

Manipulation of the molecular-axis distribution is an important ingredient in experiments aimed at understanding and controlling molecular processes(1-6). Samples of aligned or oriented molecules can be obtained following the interaction with an intense laser field(7-9), enabling experiments in the molecular rather than the laboratory frame(10-12). However, the degree of impulsive molecular orientation and alignment that can be achieved using a single laser field is limited(13) and crucially depends on the initial states, which are thermally populated. Here we report the successful demonstration of a new technique for laser-field-free orientation and alignment of molecules that combines an electrostatic field, non-resonant femtosecond laser excitation(14) and the preparation of state-selected molecules using a hexapole(2). As a unique quantum-mechanical wavepacket is formed, a large degree of orientation and alignment is observed both during and after the femtosecond laser pulse, which is even further increased (to < cos theta > = -0.74 and < cos(2)theta > = 0.82, respectively) by tailoring the shape of the femtosecond laser pulse. This work should enable new applications such as the study of reaction dynamics or collision experiments in the molecular frame, and orbital tomography(11) of heteronuclear molecules.