An optical vortex as a rotating body: mechanical features of a singular light beam

With an example of the Laguerre–Gaussian LG01 mode we show that the free-space evolution of a vortex light beam can be interpreted as the mechanical motion of a 'body' whose density is determined by the mass equivalent of the beam energy. As mechanical attributes, this 'body' possesses angular velocity and moment of inertia, in addition to the common orbital angular momentum. The beam 'body' is not rigid and its radial layers glide with respect to each other analogous to the motion occurring in fluid vortices. Absolute values of the layer velocities agree with the energy transfer rates following from the consideration of the Poynting vector distribution.