Atoms in complex twisted light

Abstract

The physics of optical vortices, also known as twisted light, is now a well-established and a growing branch of optical physics with a number of important applications and significant interdisciplinary connections. Optical vortex fields of widely varying forms and degrees of complexity can be realised in the laboratory by a host of different means. The interference between such beams with designated orbital angular momenta and optical spins (the latter is associated with wave polarisations) can be structured to conform to various geometrical arrangements. The focus of this review is on how such tailored forms of light can exert a controllable influence on atoms with which they interact. The main physical effects involve atoms in motion due to application of optical forces. The now mature area of atom optics has had notable successes both of fundamental nature and in applications such as atom lasers, atom guides and Bose-Einstein condensates. The concepts in atom optics encompass not only atomic beams interacting with light, but atomic motion in general as influenced by optical and other fields. Our primary concern in this review is on atoms in structured light where, in particular, the twisted nature of the light is made highly complex with additional features due to wave polarisation. These features bring to the fore a variety of physical phenomena not realisable in the context of atomic motion in more conventional forms of laser light. Atoms near resonance with such structured light fields become subject to electromagnetic fields with complex polarisation and phase distributions, as well as intricately structured intensity gradients and radiative forces. From the combined effect of optical spin and orbital angular momenta, atoms may also experience forces and torques involving an interplay between the internal and centre of mass degrees of freedom. Such interactions lead to new forms of processes including scattering, trapping and rotation and, as a result, they exhibit characteristic new features at the micro-scale and below. A number of distinctive properties involving angular momentum exchange between the light and the atoms are highlighted, and prospective applications are discussed. Comparison is made between the theoretical predictions in this area and the corresponding experiments that have been reported to date.

Enhanced optical activity using the orbital angular momentum of structured light

“…To date, there have been few studies of the spectroscopic application of twisted light, with work in the nascent area generally concerned with answering fundamental questions such as whether optical OAM could be involved in atomic electronic transitions [82,83]. Interestingly, a few exploratory studies on spectroscopic applications of structured light possessing OAM and optical activity have indicated that such a chiroptical effect is possible [84,85], and the same group has recently published work where recognizable chiroptical effects occur in the transmission of vortex beams though mouse brain tissue [86].…”

Quantum electrodynamics in modern optics and photonics: tutorial

“…Nonetheless, the same QED methods are highly amenable to application in the sphere of structured light [207], leading, for example, to the discovery that it is possible to deliver vortex photons by direct emission from suitably excited arrays [208][209][210] and so paving the way for a range of technical developments and implementations [211][212][213][214][215][216]. Whether the optical orbital angular momentum (OAM) of structured light could be transferred to the internal electronic degrees of freedom of an atom or molecule has been a well-debated topic, with highly significant implications in spectroscopy [217]. The first attempt at tackling this question utilized QED methods and determined that, for dipole transitions, the OAM of light is transferred to the mechanical motion of particles only; the lowest-order interaction required for OAM to be transferred to an electron is through E2 transitions [218].…”

Atom trapping and dynamics in the interaction of optical vortices with quadrupole-active transitions

“…with the corresponding quadrupole potential given by Eq. (8). In the following, we focus on the specific case of the Cs atom, which has been the subject of investigation involving its quadrupole transition (6 2 S 1/2 → 5 2 D 5/2 ).…”