Transverse spinning of unpolarized light

It is well known that the spin angular momentum of light, and therefore that of photons, is directly related to their circular polarization. Naturally, for totally unpolarized light, polarization is undefined and the spin vanishes. However, for non-paraxial light, the recently discovered transverse spin component, orthogonal to the main propagation direction, is largely independent of the polarization state of the wave. Here, we demonstrate, both theoretically and experimentally, that this transverse spin survives even in non-paraxial fields (for example, focused or evanescent) generated from totally unpolarized paraxial light. This counterintuitive phenomenon is closely related to the fundamental difference between the meanings of 'full depolarization' for two-dimensional (2D) paraxial and 3D non-paraxial fields. Our results open an avenue for studies of spin-related phenomena and optical manipulation using unpolarized light.

Automated summary

This study demonstrates the existence of a transverse spin component in non-paraxial light, which is independent of the circular polarization state of the light. The results show that this transverse spin remains present even in non-paraxial fields generated from totally unpolarized light, suggesting a fundamental difference in the meaning of 'full depolarization' between 2D paraxial and 3D non-paraxial fields. This discovery opens up new avenues for investigating spin-related phenomena and optical manipulation using unpolarized light.