I will overview recent theoretical and experimental studies, which revisit fundamental dynamical properties of light: momentum and angular momentum. I will show that the commonly accepted approach based on the use of the Poynting vector and the corresponding angular momentum does not work well for optical fields and laboratory experiments. An alternative approach requires revisiting the electromagnetic field theory and its connection with optics and quantum mechanics. It turns out that the canonical(rather than kinetic) field-theory picture of gauge-dependent momentum and spin densities of the massless electromagnetic field is perfectly consistent with the laboratory optical experience, provided that the Coulomb gauge is chosen.
The above analysis is not of purely theoretical interest. This new ‘canonical’ approach to the momentum and angular momentum of light has allowed us to predict qualitatively new types of the spin and momentum in structured optical fields [1–5]. These are:
1. The transverse spin angular momentum, which is orthogonal to the wave vector and is independent of the helicity;
2. The anomalous transverse momentum, which depends on the helicity of light and exerts a weak anomalous optical pressure orthogonal to the wave vector.
Both these quantities have attracted considerable attention and have been described and measured experimentally in several optical systems.
Konstantin Bliokh received a Ph.D. degree in physics from Kharkov National University (Ukraine) in 2001. After that, he worked at the Institute of Radio Astronomy (Ukraine), was a post-doctoral fellow at Bar-Ilan University (Israel, 2003–2005), a visiting research scientist at Technion–Israel Institute of Technology (Israel, 2007), a Linkage International research fellow at the Australian National University (Australia, 2008–2009), Marie Curie research fellow at the National University of Ireland (Ireland, 2009–2011), and research fellow in RIKEN (Japan, 2011–2015). He is currently a Future Fellow (level D) at Nonlinear Physics Centre (RSPE, ANU). His ongoing research areas include: geometric phases; spin-orbit interactions; momentum and angular momentum; quantum vortices; relativistic wave equations; wave propagation, localization, and scattering in inhomogeneous media; quantum weak measurements; plasmonics and metamaterials; coupling and resonances. His scientific results have been published in ~100 per-reviewed full-length papers, reviews, and book chapters.