Spin–orbit coupling induced by ascorbic acid crystals

Abstract

Some anisotropic materials form semicrystalline structures, called spherulites, when observed in a polarisation microscope, exhibit a characteristic “maltese-cross”-like pattern. While this observation has been hitherto considered as a tool to characterize these materials, we show that these patterns are associated with a strong light’s spin–orbit coupling induced by the spherulite structures. We experimentally demonstrate these effects using samples of crystallized ascorbic acid and observing the creation of optical vortices in transmitted laser beams, as well as the formation of inhomogeneous polarisation patterns. Our findings suggest the use of some spherulites based on other materials in frequency ranges, e.g. in the THz domain, where polarisation and spatial shaping of electromagnetic radiation is still a challenging task.

Recent advances in spin-orbit photonic technologies

“…We observe the same functionality in samples of crystallized ascorbic acid, suggesting that spherulites based on other materials might enable spin-orbit effects in more challenging spectral regimes. 7 The functionality of standard q-plates can be extended to generate Airy and Bessel beams, 8 or any arbitrary phase modulation, 9 limited only by the fabrication facility. Moreover, novel liquid-crystal plates, which we referred to as dual-q-plates, where the front and back alignment layers exhibit different topologies, 10 can also be designed.…”