Optical Chirality Flux as a Useful Far-Field Probe of Chiral Near Fields

Poulikakos, Lisa V.; Gutsche, Philipp; McPeak, Kevin M.; Burger, Sven; Niegemann, Jens; Hafner, Christian; Norris, David J.

doi:10.1021/acsphotonics.6b00201

Cited by 99 publications

(148 citation statements)

References 60 publications

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“…For absorption-less scattering objects consisting of isotropic materials, the conversion of helicity due to the scatterer vanishes when the integrated optical chirality flux into the structure is equal to the integrated outgoing flux. 35,36 We see in The symmetry of the disk upon reflection across any plane containing the optical axis ensures that the results for incident right circularly polarized light would be identical except for a sign change in the signed quantities. From these calculations it can be concluded that the cylinder meets the three requirements, and can act as an approximately helicity preserving source of chiral near-fields for enhanced CD measurements.…”

Section: Resultsmentioning

confidence: 99%

Achiral, Helicity Preserving, and Resonant Structures for Enhanced Sensing of Chiral Molecules

et al. 2019

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We design a planar array of connected silicon disks for improved molecular circular dichroism measurements in the near infrared. Full wave simulations demonstrate a volume averaged five-fold enhancement of the circular dichroism signal under normal illumination at the operating frequency. The enhancement is achieved by optimizing the disks according to three design requirements: Helicity preservation to obtain nearfields of pure handedness, spatial inversion symmetries to avoid introducing biases, and a resonant response to obtain large near-field amplitudes. The understanding and formalization of the requirements, and the analysis and optimization of the structures is facilitated by the Riemann-Silberstein representation of electromagnetic fields.Chiral objects are omnipresent in and all around us. Ranging from the double-helical structure of our DNA, extending over our hands -that originally lent the property its name -up to the spiral galaxies in the sky. Chiral objects, which are not super-imposable onto their mirror images by any translation or rotation, play a fundamental role in modern science as well as life itself. The reason for which living nature tends to have a bias for molecules and macroscopic structures of a certain handedness, is still one of its greatest secrets. 1 Apart from the fundamental questions arising due to the violation of mirror symmetry in the laws of our universe, we often deal with more pragmatic problems. Enantiomers, being pairs of mirror-image chiral molecules, often react differently in biological organisms due to the chiral specifications of the cells' receptors. As a result, drugs consisting of chiral molecules can have profoundly different therapeutic and/or toxicological properties. 2 Sharing the same atomic composition, pairs of enantiomers are indistinguishable when measuring their scalar physical properties. It is only in the interaction with other chiral objects, that they unveil their chiral nature. In optics, the most common chiral object that is dealt with is circularly polarized light (CPL). Upon interaction with light, a chiral molecule exhibits a preferential absorption for either left or right circular polarization, measured by means of circular dichroism (CD) spectroscopy. In a traditional CD setup, the molecular solution is sequentially illuminated by propagating beams of different polarization handedness, and the total outgoing power is recorded in each case. The CD signal is the difference between the two power measurements. Chiral light-matter interactions, however, are typically of small magnitude compared to the achiral interactions. For samples of low molecular concentration, the impossibility of indefinitely increasing the illumination power leads to long measurement times, often of several hours cite**, that are needed in order to elevate the CD signal over the noise. Moreover, some envisioned applications e.g. in the context of lab-on-a-chip, require the testing of minute quantities of analytes in small volumes that are not easily accessed by a focused...

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Section: Resultsmentioning

confidence: 99%

Achiral, Helicity Preserving, and Resonant Structures for Enhanced Sensing of Chiral Molecules

et al. 2019

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“…Nonetheless, one can determine the electron velocity en v j ) [55,57,59,69]. It should be emphasized that K is the helicity density, but not the chirality density (Lipkin's zilch); these quantities are simply proportional to each other only in free space [57,77,[98][99][100][101][102]. Similarly to equation (2.17), for a plane wave in a homogeneous transparent medium, equation (5.1) yields:…”

Section: Magnetization Magnetization Current and Abraham Momentummentioning

confidence: 98%

Optical momentum and angular momentum in complex media: from the Abraham–Minkowski debate to unusual properties of surface plasmon-polaritons

2017

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We examine the momentum and angular momentum (AM) properties of monochromatic optical fields in dispersive and inhomogeneous isotropic media, using the Abraham-and Minkowski-type approaches, as well as the kinetic (Poynting-like) and canonical (with separate spin and orbital degrees of freedom) pictures. While the kinetic Abraham-Poynting momentum describes the energy flux and the group velocity of the wave, the Minkowski-type quantities, with proper dispersion corrections, describe the actual momentum and AM carried by the wave. The kinetic Minkowski-type momentum and AM densities agree with phenomenological results derived by Philbin. Using the canonical spinorbital decomposition, previously used for free-space fields, we find the corresponding canonical momentum, spin and orbital AM of light in a dispersive inhomogeneous medium. These acquire a very natural form analogous to the Brillouin energy density and are valid for arbitrary structured fields. The general theory is applied to a non-trivial example of a surface plasmon-polariton (SPP) wave at a metal-vacuum interface. We show that the integral momentum of the SPP per particle corresponds to the SPP wave vector, and hence exceeds the momentum of a photon in the vacuum. We also provide the first accurate calculation of the transverse spin and orbital AM of the SPP. While the intrinsic orbital AM vanishes, the transverse spin can change its sign depending on the SPP frequency. Importantly, we present both macroscopic and microscopic calculations, thereby proving the validity of the general phenomenological results. The microscopic theory also predicts a transverse magnetization in the metal (i.e. a magnetic moment for the SPP) as well as the corresponding direct magnetization current, which provides the difference between the Abraham and Minkowski momenta.

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“…The practical use of other less well known conservation laws is being investigated. For example, the helicity conservation law is being considered in the context of chiral light-matter interactions [1][2][3][4]. The effects of the conservation laws of the two transverse components of angular momentum are also under scrutiny [2,[5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Unified theory to describe and engineer conservation laws in light-matter interactions

Fernandez‐Corbaton

Rockstuhl

2017

Phys. Rev. A

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The effects of the electromagnetic field on material systems are governed by joint light-matter conservation laws. An increasing number of these balance equations are currently being considered both theoretically and with an eye to their practical applicability. We present a unified theory to treat conservation laws in light-matter interactions. It can be used to describe and engineer the transfer of any measurable property from the electromagnetic field to any object. The theory allows to explicitly characterize and separately compute the transfer due to asymmetry of the object and the transfer due to field absorption by the object. It also allows to compute the upper bound of the transfer rate of any given property to any given object, together with the corresponding most efficient illumination which achieves the bound. Due to its algebraic nature, the approach is inherently suited for computer implementation.

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Optical Chirality Flux as a Useful Far-Field Probe of Chiral Near Fields

Cited by 99 publications

References 60 publications

Achiral, Helicity Preserving, and Resonant Structures for Enhanced Sensing of Chiral Molecules

Achiral, Helicity Preserving, and Resonant Structures for Enhanced Sensing of Chiral Molecules

Optical momentum and angular momentum in complex media: from the Abraham–Minkowski debate to unusual properties of surface plasmon-polaritons

Unified theory to describe and engineer conservation laws in light-matter interactions

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