Control of molecular rotation in the limit of extreme rotational excitation

TL;DR

This paper reviews recent advances in controlling molecular rotation at extreme excitation levels, focusing on experimental techniques to produce and detect molecular superrotors with potential applications in various fields.

Contribution

It introduces and compares two experimental methods for generating uni-directional rotational wave packets and outlines three detection techniques for characterizing superrotor states.

Findings

Successful demonstration of high rotational excitation techniques

Effective detection methods for superrotor states

Potential applications in anisotropic diffusion and THz radiation

Abstract

Laser control of molecular rotation is an area of active research. A number of recent studies has aimed at expanding the reach of rotational control to extreme, previously inaccessible rotational states, as well as controlling the directionality of molecular rotation. Dense ensembles of molecules undergoing ultrafast uni-directional rotation, known as molecular superrotors, are anticipated to exhibit unique properties, from spatially anisotropic diffusion and vortex formation to the creation of powerful acoustic waves and tuneable THz radiation. Here we describe our recent progress in controlling molecular rotation in the regime of high rotational excitation. We review two experimental techniques of producing uni-directional rotational wave packets with a "chiral train" of femtosecond pulses and an "optical centrifuge". Three complementary detection methods, enabling the direct observation, characterization and control of the superrotor states, are outlined: the one based on coherent Raman scattering, and two other methods employing both resonant and non-resonant multi-photon ionization. The capabilities of the described excitation and detection techniques are demonstrated with a few examples. The paper is concluded with an outlook for future developments.