Eur. Phys. J. D (2012) 66: 167
https://doi.org/10.1140/epjd/e2012-30061-1

Regular Article

Electromagnetic angular momentum flux tensor in a medium

Aalto University, Department of Applied Physics, P.O. Box 13500, 00076 AALTO, Finland

^a e-mail: andriy.shevchenko@aalto.fi

Received: 24 January 2012
Received in final form: 6 April 2012
Published online: 29 June 2012

Abstract

Electromagnetic angular momentum describes the ability of electromagnetic field to impose torque on matter. We show that for an electromagnetic field – such as an optical beam field – in a medium, the torque density is determined by two fundamental quantities: the angular momentum flux tensor and the angular momentum density of the field. It is remarkable that the tensor alone gives the full picture of the angular momentum transfer between the field and the medium in all stationary electromagnetic phenomena. We derive a general expression for this tensor and apply the theory to several important examples without resorting to the classical paraxial approximation.