Optical Helicity and Optical Chirality in Free Space and in the Presence of Matter

Abstract

The inherently weak nature of chiral light–matter interactions can be enhanced by orders of magnitude utilizing artificially-engineered nanophotonic structures. These structures enable high spatial concentration of electromagnetic fields with controlled helicity and chirality. However, the effective design and optimization of nanostructures requires defining physical observables which quantify the degree of electromagnetic helicity and chirality. In this perspective, we discuss optical helicity, optical chirality, and their related conservation laws, describing situations in which each provides the most meaningful physical information in free space and in the context of chiral light–matter interactions. First, an instructive comparison is drawn to the concepts of momentum, force, and energy in classical mechanics. In free space, optical helicity closely parallels momentum, whereas optical chirality parallels force. In the presence of macroscopic matter, the optical helicity finds its optimal physical application in the case of lossless, dual-symmetric media, while, in contrast, the optical chirality provides physically observable information in the presence of lossy, dispersive media. Finally, based on numerical simulations of a gold and silicon nanosphere, we discuss how metallic and dielectric nanostructures can generate chiral electromagnetic fields upon interaction with chiral light, offering guidelines for the rational design of nanostructure-enhanced electromagnetic chirality.

Chirality Transfer from Sub‐Nanometer Biochemical Molecules to Sub‐Micrometer Plasmonic Metastructures: Physiochemical Mechanisms, Biosensing, and Bioimaging Opportunities

“…[39,43] Together with theories that can elegantly describe the interaction between chiral molecules and plasmonic nanostructures, [44][45][46][47] the study of chirality has entered a fast development path. There have been several reviews focusing on various aspects of this field, including fabrication, [39,43,48,49] theories, [50][51][52] and applications. [38,53,54] The goal of the present review, as illustrated in Scheme 1, is to elaborate the three physiochemical mechanisms of chirality transfer from sub-nanometer biochemical molecules to submicrometer metallic nanostructures, namely electromagnetic interaction induced chirality transfer, chiral assembly and chirality inheritance, molecular conformation change induced chirality.…”

Kerker Conditions upon Lossless, Absorption, and Optical Gain Regimes

“…On the other hand, for cylindrically symmetric particles, the absence of backscattered light follows from the preservation of EM helicity [14][15][16][17][18]. Conservation of helicity has proven crucial in many applications such as enhanced chiral light-matter interactions [19][20][21][22][23][24][25], or in the spin-orbit interactions of light [26][27][28][29][30][31][32]. In this vein, it has been reported that from a relatively simple far-field measurement of the EM helicity at a right angle, the radiation pattern of the dipolar particle is inferable [33].…”

Cubic 3D Chern photonic insulators with orientable large Chern vectors

“…4(f), integrating the total contribution of entire SS yields no net energy transport along the bias field, as expected due to equilibrium conditions (see SI section B.2). Interestingly, analyzing the polarization state of each edge channel, we observe a well defined sign of the spatially-averaged opti-cal chiralityc > 0 [42][43][44][45][46][47] through the entire SS (see SI section B.3).…”