Abstract
Abstract The insight that optical vortex beams carry orbital angular momentum (OAM), which emerged in Leiden about 30 years ago, has since led to an ever expanding range of applications and follow-up studies. This paper starts with a short personal account of how these concepts arose. This is followed by a description of some recent ideas where the coupling of transverse orbital and spin angular momentum (SAM) in tightly focused laser beams produces interesting new effects. The deflection of a focused light beam by an atom in the focus is reminiscent of the Magnus effect known from aerodynamics. Momentum conservation dictates an accompanying light force on the atom, transverse to the optical axis. As a consequence, an atom held in an optical tweezer will be trapped at a small distance of up to λ/2π away from the optical axis, which depends on the spin state of the atom and the magnetic field direction. This opens up new avenues to control the state of motion of atoms in optical tweezers as well as potential applications in quantum gates and interferometry.
Highlights
The notion that Laguerre–Gaussian (LG) optical modes carry orbital angular momentum (OAM) of light emerged some thirty years ago [1]
An atom held in an optical tweezer will be trapped at a small distance of up to λ∕2π away from the optical axis, which depends on the spin state of the atom and the magnetic field direction
A brief personal, historical account of the days that saw the emergence of OAM has been presented
Summary
The notion that Laguerre–Gaussian (LG) optical modes carry orbital angular momentum (OAM) of light emerged some thirty years ago [1]. In this paper I will give a brief personal account of how the concept of OAM first arose in Woerdman’s quantum optics group in Leiden This is followed by a discussion of some new ideas with possible applications [32]. It should be noted that other optical analogies of the Magnus effect have been reported before These earlier works concerned the rotation of the spatial profile of an optical beam, by coupling to the circular polarization [34–39]. This effect has been described in terms of Berry phases and is closely related to the spin-Hall effect of light [40–42]. This has important consequences for optical tweezers: atoms can be trapped off-axis at a spin-dependent distance from the focus [43]
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