Angular Momentum Of Light Beam Research Articles

The angular momentum of light: optical spanners and the rotational frequency shift

An introduction is given to the concepts of the spin and orbital angular momentum of light beams. Both spin and orbital angular momentum can be transferred from a light beam to particles held within optical tweezers, so forming an optical spanner. Each also give rise to a frequency shift when the light beam is rotated. This arises because quarter or half-wave plates and π/2 or π mode converters play equivalent roles for spin and orbital angular momentum respectively.

Topological charge and angular momentum of light beams carrying optical vortices

We analyze the properties of light beams carrying phase singularities, or optical vortices. The transformations of topological charge during free-space propagation of a light wave, which is a combination of a Gaussian beam and a multiple charged optical vortex within a Gaussian envelope, are studied both in theory and experiment. We revise the existing knowledge about topological charge conservation, and demonstrate possible scenarios where additional vortices appear or annihilate during free propagation of such a combined beam. Coaxial interference of optical vortices is also analyzed, and the general rule for angular-momentum density distribution in a combined beam is established. We show that, in spite of any variation in the number of vortices in a combined beam, the total angular momentum is constant during the propagation.