Transverse and longitudinal angular momenta of light

Understand

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.