Near-field polarization analysis for an optical nanofiber

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During the year, the polarization control in optical nanofibres has been further improved enabling studies on spin-orbit coupling for optically trapped chiral particles adjacent to an optical nanofibre. Spin angular momentum in electromagnetic waves is caused not only by field rotations associated with elliptical polarization, but also by spatial modulations of the field. Consequently, the spin carried by light does not have to be parallel to the energy transfer. Transverse components can be significant in strongly confined light, such as evanescent fields. Here, the transverse spin was revealed through its direct action on a probe particle held and spun by optical tweezers in the evanescent field at the surface of a nanofiber. The work has benefitted from a theoretical model developed by colleagues in ITMO, Russia. This work has been presented at several conferences (including OPIC 2021) and is being prepared for publication.A second work has also been conducted building on the polarization control. Composite material objects such as Janus particles can exhibit interesting dynamics, such as propulsion in response to an external gradient field or collective assembly due to a generated localized thermal gradient around each particle. In this study, we demonstrated light-induced dynamics of metallo-dielectric Janus microspheres with a thin layer of gold that are trapped and propelled in the evanescent field of a nanofiber. We found that Janus particles with a 10 nm or 20 nm gold coating exhibit propulsion speed enhancements compared with uncoated silica microspheres.