Discrimination of Chiral and Helical Contributions to Raman Scattering of Liquid Crystals Using Vortex Beams

We use vortex photon fields with orbital and spin angular momentum to probe chiral fluctuations within liquid crystals. In the regime of iridescence with a well-defined pitch length of chirality, we find low energy Raman scattering that can be decomposed into helical and chiral components depending on the scattering vector and the topological charge of the incident photon field. Based on the observation of an anomalous dispersion we attribute quasi-elastic scattering to a transfer of angular momenta to roton-like quasiparticles. The latter are due to a competition of short-range repulsive and long-range dipolar interactions. Our approach using a transfer of orbital angular momentum opens up an avenue for the advanced characterization of chiral and optically active devices and materials.
Comment: 5 pages, 3 figures, Physical Rev. Lett., in print (2022)