Conservation of the spin angular momentum in second-harmonic generation with elliptically polarized vortex beams

Abstract

Spin-to-orbital angular momentum conversion and orbital angular momentum conservation in the harmonic generation process have been extensively investigated. However, very few studies have focused on the spin angular momentum (SAM) conservation in the nonlinear optical process. Herein, we investigate the SAM characteristics of the second-harmonic waves with weakly focused elliptically polarized vortex beams (EPVBs). It is shown that the chirality of the second-harmonic wave is always opposite to that of the fundamental wave. Moreover, the absolute value of SAM satisfies the conservation law in the second-harmonic process generated by weakly focused EPVBs. The results are in good agreement with the experimental observations.