Optical chirality of vortex beams at the nanoscale

Abstract

In this work we undertake a systematic study of the optical chirality density of Laguerre-Gaussian and Bessel laser beams tightly focused into nanoscale volumes. In particular we highlight the unique...

Fundamental symmetry origins in the chiral interactions of optical vortices

“…However, with substantially higher values of l , additional features may begin to show their effect, as terms associated with quadratic response (e.g., from two E2 interactions, or one E2 with one M2) may be grow in significance sufficiently to offset the higher overall order of multipoles involved. Such features have been identified in several recent studies 111,114 …”

“…The present analysis relates to beams of cylindrical symmetry in the electromagnetic field amplitudes and intensities. An additional tier of experimental possibility arises when vortex beams are subjected to a tight focus, as, for example, on passage through a high numerical aperture lens, when even unpolarized light can engender enantioselective interactions 111,114 . Under these conditions, where cylindrical symmetry is retained, the transverse profile of the beam the radial distribution of helicity can nonetheless alternate in sign, so that the extent and sign of any enantioselection—in circular dichroism, for example—will vary radially from the beam center.…”

“…In both cases, the answer is undoubtedly yes-as numerous studies, both theoretical and experimental, have shown. 78,80,82,94,[96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112] The result of vortex interactions involving electric quadrupole interference terms is that measurables such as absorption coefficients or scattering intensities display a linear dependence on the experimental variable l, that is, the associated rate equation takes the form Γ $ al þ Γ 0 , where Γ 0 signifies a result obtainable with non-vortex light. The number of molecular invariants in the detailed structure of the constants a and Γ 0 is independent of the means of excitation; both a and b share the same dependence on the intensity of the optical input.…”

“…Two linked questions of experimental significance arise: Does the engagement of structured light lead to a greater number of experimental observables; if so, is it then possible to determine a greater amount of information on the physical properties or structures of chiral systems, by such means? In both cases, the answer is undoubtedly yes—as numerous studies, both theoretical and experimental, have shown 78,80,82,94,96–112 . The result of vortex interactions involving electric quadrupole interference terms is that measurables such as absorption coefficients or scattering intensities display a linear dependence on the experimental variable l , that is, the associated rate equation takes the form , where signifies a result obtainable with non‐vortex light.…”

Influence of polarization on the optical chirality of vortex beams

“…they are linearly polarized or unpolarized. For more details the reader is referred to references 9,13,14 . It is crucial to point out that when we speak of polarization in this work, we explicitly mean the two-dimensional (2D) polarization state, i.e., that of the paraxial transverse electromagnetic fields in the far field, and not that of the polarization of the field around the focal plane, which is described by the three-dimensional (3D) state of polarization due to the generation of significant longitudinal electromagnetic fields.…”