Paraxial Light Beams with Angular Momentum
  Fundamental and applied concepts concerning the ability of light beams to carry a certain mechanical angular momentum with respect to the propagation axis are reviewed and discussed. Following issues are included:   Historical reference;   Angular momentum of a paraxial beam and its constituents;   Spin angular momentum and paradoxes associated with it;   Orbital angular momentum;   Circularly-spiral beams: examples and methods of generation;   Orbital angular momentum and the intensity moments;   Symmetry breakdown and decomposition of the orbital angular momentum;   Mechanical models of the vortex light beams;   Mechanical action of the beam angular momentum;   Rotational Doppler effect, its manifestation in the image rotation;   Spectrum of helical harmonics and associated problems;   Non-collinear rotational Doppler effect;   Properties of a beam forcedly rotating around its own axis.   Research prospects and ways of practical utilization of optical beams with angular momentum. 
A. Bekshaev, M.Soskin, M.Vasnetsov