Sur le moment d'impulsion d'une onde électromagnétique

The decomposition of the angular momentum of the electromagnetic radiation in three terms has been studied; two of these terms present a formal resemblance with an orbital-momentum and a spin-momentum - respectively; the third one, which is a surface term, has often been wrongly neglected. A new form, corresponding to this decomposition, is given for the flux of angular momentum; it allows to make the calculation of this flux without it being necessary to know the terms of potentials and fields which have the magnitude of 1/ R² (in particular, without the knowledge of longitudinal fields).

The general considerations of the first paragraph have been applied to the electric dipole radiation, in order to elucidate a paradox pointed out by J. Géhéniau for de Broglie's photon theory.

The case of the plane wave is also studied within the frame of the first paragraph. Abraham-Sommerfeld's formula is established for a quasiplane wave. Finally, it is pointed out that there exists an ambiguity in the definition for the angular momentum of a rigorously plane wave.