Transverse and longitudinal angular momenta of light

By K. Bliokh, Franco Nori. 2015

848 citations recorded by the source corpus.

We review basic physics and novel types of optical angular momentum. We start with a theoretical overview of momentum and angular momentum properties of generic optical fields, and discuss methods for their experimental measurements. In particular, we describe the well-known longitudinal (i.e., aligned with the mean momentum) spin and orbital angular momenta in polarized vortex beams. Then, we focus on the transverse (i.e., orthogonal to the mean momentum) spin and orbital angular momenta, which were recently actively discussed in theory and observed in experiments. First, the recently-discovered transverse spin angular momenta appear in various structured fields: evanescent waves, interference fields, and focused beams. We show that there are several kinds of transverse spin angular momentum, which differ strongly in their origins and physical properties. We describe extraordinary features of the transverse optical spins and overview recent experiments. In particular, the helicity-independent transverse spin inherent in edge evanescent waves offers robust spin-direction coupling at optical interfaces (the quantum spin Hall effect of light). Second, we overview the transverse orbital angular momenta of light, which can be both extrinsic and intrinsic. These two types of the transverse orbital angular momentum are produced by spatial shifts of the optical beams (e.g., in the spin Hall effect of light) and their Lorentz boosts, respectively. Our review is underpinned by a unified theory of the angular momentum of light based on the canonical momentum and spin densities, which avoids complications associated with the separation of spin and orbital angular momenta in the Poynting picture. It allows us to construct comprehensive classification of all known optical angular momenta based on their key parameters and main physical properties.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/c425be4a8957161e797bb21238385f6e2b247e32

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Citations in the corpus

Roadmap on structured light (2016, background): “At the most fundamental level there are new, unresolved questions about the character of the photon, andthe capacity of widely accepted photon representations to adequately capture the properties of structured beams as conveyed by classical representations [17].”
(INVITED) Vortex solitons: Old results and new perspectives (2019, background): “It is relevant to mention too that vortices are closely related to the concept of the optical angular momentum [111–113], and the possibility of storage of the angular momentum in ultracold gases [114].”
Structured Light: Ideas and Concepts (2020, background): “The orbital momentum (OM) (17) immediately enters the energy-momentum tensor [7] and appears in the general field-theory formalism from the field Lagrangian and the momentum conservation via the Noether theorem [12, 58] (that is why it is also called “canonical”).”
Theory and applications of free-electron vortex states (2017, background): “In the past two decades, five books [55, 56, 57, 58, 59] and many reviews [60, 61, 62, 63, 64, 65, 66] about optical vortex beams and OAM were published.”
Photonic spin Hall effect in metasurfaces: a brief review (2017, background): “The momentum of light can be divided into linear and angular contributions [41].”