Optimally Chiral Light: Upper Bound of Helicity Density of Structured Light for Chirality Detection of Matter at Nanoscale

Hanifeh, Mina; Albooyeh, Mohammad; Capolino, Filippo

doi:10.1021/acsphotonics.0c00304

Cited by 25 publications

(55 citation statements)

References 95 publications

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“…In the context of light-matter interactions the role of such reference is played by the polarization handedness of light, or, more fundamentally, the electromagnetic helicity. The role of helicity in chiral light-matter interactions is under intense scrutiny [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. We can split any electromagnetic field into two components of opposite helicity, left-handed and right-handed, corresponding to eigenstates of the helicity operator Λ with eigenvalues λ = 1 and λ = −1, respectively.…”

Section: Electromagnetic Helicity As Chirality Referencementioning

confidence: 99%

Multidimensional measures of electromagnetic chirality and their conformal invariance

Vavilin

Fernandez‐Corbaton

2022

New J. Phys.

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Proper assignment of left- and right-handed labels to general chiral objects is known to be a theoretically unfeasible problem. Attempts to utilize a pseudoscalar function to distinguish enantiomers face two unavoidable difficulties: false chiral zeros and unhanded chiral states. In here, we demonstrate how both of these problems can be solved in the context of light-matter interactions. First, we introduce a two-dimensional quantity called complex electromagnetic chirality that solves the problem of false chiral zeros. Next, we define an infinite-dimensional pseudovector called chirality signature that completely quantifies the multidimensional nature of electromagnetic chirality, does not have false global chiral zeros, and allows to continuously distinguish any pair of enantiomers because it does not produce unhanded chiral states. We prove that the introduced measures are invariant under the largest group of symmetries of Maxwell’s equations – the conformal group. The complete, continuous, and conformally invariant quantification of electromagnetic chirality provided by the chirality signature distinguishes it as a particularly suitable tool for the study of chirality and its applications.

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Section: Electromagnetic Helicity As Chirality Referencementioning

confidence: 99%

Multidimensional measures of electromagnetic chirality and their conformal invariance

Vavilin

Fernandez‐Corbaton

2022

New J. Phys.

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“…[34] The chirality parameter κ is an empirical quantity that provides the chiral strength of the material under consideration. We can next relate the electric, magnetic and electro-magnetic polarizabilities through the material parameters by using Mie scattering theory as: [17,29,39]…”

Section: Mie Scattering Formalismmentioning

confidence: 99%

“…Conversely, a chiral tip having solely transverse chirality with α em,xx = α em,yy = α em and α em,zz = 0 produces a map that reports on the central transverse helicity density, as shown in 4(f). In the supporting information, we also present the helicity density maps determined with the differential force of a focused azimuthally radially polarized beam (ARPB) [17,31,47].…”

Section: Full Wave Simulationsmentioning

confidence: 99%

“…The chiral state of light is related to the curled character of the electric and magnetic fields. The quantity commonly used for quantifying this 'degree of curliness' is the timeaveraged helicity density [14,15], which is defined as h = 1 2ωc Im(E • H * ), where E and H are the phasor electric and magnetic field at angular frequency ω, and c is the speed of light ( * denotes complex conjugation) [16,17]. The helicity density is a time-even, pseudo-scalar conserved quantity that corresponds to the difference between the numbers of RCP and LCP photons [14,15,18].…”

Section: Introductionmentioning

confidence: 99%

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Force Detection of Electromagnetic Beam Chirality at the Nanoscale

Sifat¹,

Capolino²,

Potma³

2021

Preprint

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Many nanophotonic applications require precise control and characterization of electromagnetic field properties at the nanoscale. The chiral properties of the field are among its key characteristics, yet measurement of optical chirality at dimensions beyond the diffraction limit has proven difficult.Here we theoretically show that the chiral properties of light can be characterized down to the nanometer scale by means of force detection. We demonstrate that the photo-induced force exerted on a sharp chiral tip, subjected to sequential illumination by two circularly polarized beams of opposite handedness, provides a useful probe of the chirality of the electromagnetic field. The gradient force difference ∆ F grad,z is found to have exclusive correspondence to the time-averaged helicity density, whereas the differential scattering force provides information about the spin angular momentum density of light. We further characterize and quantify the helicity-dependent ∆ F grad,z using a Mie scattering formalism complemented with full wave simulations, underlining that the magnitude of the difference force is within an experimentally detectable range.

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“…However, shortly after, it was demonstrated [8] that high refractive index particles could approximately conserve helicity due to their electric and magnetic resonances [9,10]. Since then, a lot of work has been done to characterize the role of helicity in light-matter interactions [11][12][13][14], as well as to study its relation with chirality [15][16][17][18].…”

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confidence: 99%