Second-harmonic generation of spatiotemporal optical vortices and conservation of orbital angular momentum

A spatiotemporal optical vortex (STOV) is an intrinsic optical orbital angular momentum (OAM) structure in which the OAM vector is orthogonal to the propagation direction Optica 6 , 1547 ( 2019 ) OPTIC8 2334-2536 10.1364/OPTICA.6.001547 and the optical phase circulates in space-time. Here, we experimentally and theoretically demonstrate the generation of the second harmonic of a STOV-carrying pulse along with the conservation of STOV-based OAM. Our experiments verify that photons can have intrinsic orbital angular momentum perpendicular to their propagation direction.