Polarized evanescent waves reveal trochoidal dichroism

Abstract

Matter’s sensitivity to light polarization is characterized by linear and circular polarization effects, corresponding to the system’s anisotropy and handedness, respectively. Recent investigations into the near-field properties of evanescent waves have revealed polarization states with out-of-phase transverse and longitudinal oscillations, resulting in trochoidal, or cartwheeling, field motion. Here, we demonstrate matter’s inherent sensitivity to the direction of the trochoidal field and name this property trochoidal dichroism. We observe trochoidal dichroism in the differential excitation of bonding and antibonding plasmon modes for a system composed of two coupled dipole scatterers. Trochoidal dichroism constitutes the observation of a geometric basis for polarization sensitivity that fundamentally differs from linear and circular dichroism. It could also be used to characterize molecular systems, such as certain light-harvesting antennas, with cartwheeling charge motion upon excitation.

Nanophotonic Approaches for Chirality Sensing

“…Therefore, additional fundamental studies aimed at understanding the full mechanism of PCCD and superchiral field-mediated CD using plasmonic platforms are required. Moreover, while many studies focus on enhancing C , nanophotonic near-fields contain rich polarization properties, and the full use of these properties is just starting to be explored. − For example, polarized light confined to nanoscale dimensions can possess trochoidal polarizations with cycloid-like, cartwheeling field motion enabling trochoidal dichroism, which could provide complementary information to CD in the future. Furthermore, in addition to the unusual spin angular momentum of CP light, orbital angular momentum can also be introduced into structured beams, yielding highly twisted light that offers another promising route for sensitive chirality detection. − Finally, the near-fields of metamaterials provide a relatively limited volume for molecular exposure to regions of enhanced C .…”

Coupled-Dipole Modeling and Experimental Characterization of Geometry-Dependent Trochoidal Dichroism in Nanorod Trimers

“…Trochoidal dichroism, which is dichroism of evanescent waves with opposite trochoidal polarizations 59 such as those produced from total internal reflection of ±45°linearly polarized light, 60 has recently been demonstrated using L-shaped gold nanorod dimers. 35 Trochoidal polarizations are characterized by cartwheeling electric field distributions with longitudinal components. As such, the cartwheeling electric fields in trochoidal polarizations drive the AuNRT oscillator system in ways that cannot be achieved with linearly polarized light (Figure 3a, Supplementary Note 3).…”

“…While fabricating mirror-image isomers provides one route to obtaining a reversed intensity modulation, this also leads to a reversed spectral shift. 35 To design a nanoantenna that reverses only the intensity modulation, we sweep over both gap size and angular offset to produce the phase diagram of predicted I TDS shown in Figure 5. Pink boxes are used to mark the AuNRT geometries discussed herein.…”

Chiral plasmonic nanostructures: recent advances in their synthesis and applications

“…247 Besides circularly polarized light detection, McCarthy et al recently showed that nanorod dimers could be used to detect trochoidal dichroism (trochoidal field motion being both planar and rotational, producing a cartwheeling motion liked to a significant phase delay between transverse and longitudinal oscillations). 248,249…”