Unveiling the Volumetric Orbital Angular Momentum Density Flow of Light by Symmetry Breaking of its Second Harmonic

Optical orbital angular momentum (OAM) is studied these days in numerous fundamental and applicative scenarios, including for example space division-multiplex optical communication, quantum communication and particle manipulation. The shape of OAM beams depends both on the transverse coordinates and on the propagation coordinate thus exhibiting rotational energy flows that vary in three-dimensional (3D) space [1]. Despite decades of research in the field of OAM, these 3D energy flows remained experimentally hidden. This is because symmetry breaking, that allows a glimpse to the rotational nature of these flows, changes the beam shape and destructs its original “fluid” like flow.