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Physics, Optics, Transverse spinning, unpolarized light
Abstract:
It is well known that 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 nonparaxial 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 nonparaxial
fields (e.g., tightly focused or evanescent) generated from a totally
unpolarized light source. This counterintuitive phenomenon is closely related
to the fundamental difference between the degrees of polarization for 2D
paraxial and 3D nonparaxial fields. Our results open an avenue for studies of
spin-related phenomena and optical manipulation using unpolarized light.
