Optical activity in the scattering of structured light

Abstract

We observe that optical activity in light scattering can be probed using types of illuminating light other than single plane (or quasi plane) waves and that this introduces new possibilities for the study of molecules and atoms. We demonstrate this explicitly for natural Rayleigh optical activity which, we suggest, could be exploited as a new form of spectroscopy for chiral molecules through the use of illuminating light comprised of two plane waves that are counter propagating.

Linear Rayleigh and Raman scattering to the second order: Analytical results for light scattering by any scatterer of size k0d≲1/10

“…In contrast, natural Rayleigh optical activity has been reported for a handful of large chiral biological structures, including octopus sperm [35], but has thus far proved elusive for small chiral molecules [2], in spite of potential applications such as the robust assignment of absolute configuration [36]. The difficulties here might be partially overcome using structured light [37,38]. Interestingly, orientated achiral molecules can also exhibit natural optical activity via the first-order correction, embodied by the s (1) ξ [2], and partially orientated chiral molecules can exhibit natural optical activity via the zeroth-order theory, embodied by the s (0) ξ [39].…”

Chirality and the angular momentum of light

“…Consider, then, a collection of molecules clustered around the origin while being randomly oriented and illuminated by light as before. Adopting a sum over independent scatterers approach, as is appropriate for the gas phase, it is found that the intensity of Rayleigh scattering light seen at position R in the far field is essentially [101] with and R ξ the position of the ξ th molecule. It is assumed here that the direction of observation is not parallel to the direction of propagation of any of the plane waves comprising the illuminating light.…”

“…3 Explicitly, with This result for I can be applied to a single circularly polarized plane wave illuminating the molecules, in which case it reduces to the usual form [2,23,24], as it should. It can also be applied to more exotic forms of illuminating light, which opens the door to new possibilities [101]: superchiral light enables an enhancement analogous to that recently demonstrated for luminescence-detected circular dichroism [90,102,103]; σ – σ light enables the removal of unwanted, achiral background contributions to the scattered light [101] which have thus far plagued attempts to observe Rayleigh optical activity by traditional means [2]; lin ⊥ lin light, which is by itself essentially achiral, enables the extraction of chirally sensitive information when coupled with the direction of observation, in a manner that avoids spurious contributions due to circular dichroism [101]. A challenge facing such approaches is that molecules must be confined appropriately to subwavelength regions.…”

Quantum formulation for nanoscale optical and material chirality: symmetry issues, space and time parity, and observables

“…One of the main or implicit motivations for several of the recent studies in this area is the prospect of achieving, by optical means, a separation of particles-especially chiral molecules-of opposite handedness [7,10,43,[98][99][100][101][102][103][104][105][106][107][108][133][134][135][136][137][138][139][140][141][142][143][144][145]. Certainly such a capacity might have important commercial applications-notably in the pharmaceutical industry, where oppositely handed compounds can deliver drastically different effects.…”