Angular momentum in optical beams

Light beams carry energy and linear momentum, but they also transport angular momentum. In order to obtain an expression for the angular momentum carried by light we will use paraxial approximation within classical electromagnetic theory. It is found that the resulting value can be divided naturally in two parts: a polarization contribution and a spatial contribution. By analogy, those two terms are also called spin part and orbital part of the angular momentum. In order to interpret this result we will consider two beam families, Laguerre-Gauss modes and Gauss Schell-model family. Several procedures used to obtain beams with angular momentum are also mentioned. Finally, different methods used to observe and measure the angular momentum transported by light beams are briefly explained.