Surface-Enhanced Circular Dichroism Spectroscopy on Periodic Dual Nanostructures

Abstract

Increasing the sensitivity of chiral spectroscopic techniques such as circular dichroism (CD) spectroscopy is a current aspiration in the research field of nanophotonics. Enhancing CD spectroscopy depends on two complementary requirements: the enhancement of the electromagnetic fields perceived by the molecules under study and the conservation of the helicity of those fields, guaranteed by duality symmetry. In this work, we introduce a systematic method to design nanostructured dual periodic photonic systems capable of enhancing molecular CD spectroscopy resonantly. As an illustration, we engineer a dual 1D silicon nanoparticle array and show that its collective optical modes can be efficiently employed to resonantly enhance by 2 orders of magnitude the local density of optical chirality and, thus, the CD signal obtained from a given molecular sample on its vicinity.

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].…”

“…In a spin-orbit framework, this phenomenon precludes the full angular momentum exchange from spin to orbit after scattering, inhibiting the emergence of an optical vortex in the backscattering direction. Moreover, recently, massive efforts have been dedicated to maximizing the sensitivity of circular dichroism (CD) spectroscopy of chiral molecules [19][20][21][22][23][24][25]. Some of these theoretical developments have relied on meeting Kerker's first condition in high index nanoparticles to preserve the helicity of the scattered electromagnetic fields.…”

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).…”

Orientation dependence of optical activity in light scattering by nanoparticle clusters

“…The inter-particle distance is here chosen to coincide with the Kerker condition (l = 1208 nm), to combine the benefits of field enhancement and helicity preservation. 31 The elongated GoldHelix structure already illustrated that as a cluster structure extends in an anisotropic way, along at least one direction, the collective optical response becomes more dependent on the incidence direction. This can be understood from the perspective of a multipolar expansion, as used in the superposition T-matrix framework.…”