Energy currents for quasi-monochromatic fields

Abstract

Relations for the components of Poynting vector are obtained for quasi- monochromatic waves. It is shown that the behaviour of the transverse Poynting vector component is similar to that for the coherent waves. The total angular mo- mentum of the quasi-monochromatic wave can be separated into orbital and spin parts. Using the example of a Gaussian beam, we show that the spin angular mo- mentum is associated with coherence characteristics of the optical beam.