Spin-to-Intrinsic Orbital Angular Momentum Conversion in a Focused Gaussian Beam: A Paraxial Approach

It is shown that the key features of spin angular momentum conversion into intrinsic orbital angular momentum in the focal waist can be described within the paraxial approximation. This approach makes it possible to analytically reveal the mechanism responsible for the formation of longitudinal field components and to obtain correct order-of-magnitude estimates of the induced intrinsic orbital angular momentum. The obtained results are in qualitative agreement with experimental observations of spin–orbit interaction effects in focused light beams and extend the applicability of the paraxial approximation for the analysis of structured light.