Optical theorem for the conservation of electromagnetic helicity: Significance for molecular energy transfer and enantiomeric discrimination by circular dichroism

Nieto‐Vesperinas, M.

doi:10.1103/physreva.92.023813

Cited by 64 publications

(107 citation statements)

References 43 publications

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“…Because a dipolar scatterer responds only to the local helicity density K of the beam, and not to its integrated zero value, we can show arXiv:1902.01756v1 [physics.optics] 5 Feb 2019 that the dipole moment excited in the nanoparticle at λ d emits purely circularly polarized light with a handedness defined by K and, eventually, by the OAM of the incident beam. Even though this results in SAM in the far-field, since the scatterer is dual-symmetric at λ d , we observe no total generation of helicity [31,33,36]. Nevertheless, this is different for the second regime at a wavelength λ = λ d , with the scatterer breaking the duality symmetry.…”

Section: Introductionmentioning

confidence: 73%

“…Importantly, σ is the generator of the duality transformation [31] and, hence, is preserved in systems and processes that posses duality symmetry, irrespective of the underlying geometry. Typical examples of dual-symmetric pro- * sergey.nechayev@mpl.mpg.de † peter.banzer@mpl.mpg.de; http://www.mpl.mpg.de/ cesses include scattering by dual scatterers [32][33][34], propagation in piecewise-homogeneous impedance matched media [3,31,35] or focusing by an aplanatic objective designed to have equal Fresnel coefficients for s-and ppolarized incident beams [3,7,29]. Helicity is very intuitive in the far-field, where its density K reduces to the proportion of circular polarization in each individual plane-wave component.…”

Section: Introductionmentioning

confidence: 99%

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Orbital-to-spin angular momentum conversion employing local helicity

et al. 2019

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Spin-orbit interactions in optics traditionally describe an influence of the polarization degree of freedom of light on its spatial properties. The most prominent example is the generation of a spin-dependent optical vortex upon focusing or scattering of a circularly polarized plane-wave by a nanoparticle, converting spin to orbital angular momentum of light. Here, we present a mechanism of conversion of orbital-to-spin angular momentum of light upon scattering of a linearly polarized vortex beam by a spherical silicon nanoparticle. We show that focused linearly polarized Laguerre-Gaussian beams of first order ( = ±1) exhibit an -dependent spatial distribution of helicity density in the focal volume. By using a dipolar scatterer the helicity density can be manipulated locally, while influencing globally the spin and orbital angular momentum of the beam. Specifically, the scattered light can be purely circularly polarized with the handedness depending on the orbital angular momentum of the incident beam. We corroborate our findings with theoretical calculations and an experimental demonstration. Our work sheds new light on the global and local properties of helicity conservation laws in electromagnetism.

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Section: Introductionmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Orbital-to-spin angular momentum conversion employing local helicity

et al. 2019

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“…The observed effect can be understood by considering the helicity conservation laws, symmetry and the duality properties of our system [12][13][14][15][16]. Electric-dipole scat-terers break the electromagnetic duality symmetry by reacting selectively to electric field only.…”

Section: Discussionmentioning

confidence: 99%

“…Thirdly, helicity is extinct by a scatterer positioned at a point where the helicity density of the excitation field K ψ foc is zero, in sharp contrast to the mechanism of energy extinction that requires non-zero energy density [19,33]. Lastly, it is remarkable that the scattered helicity ∝ (p · m * ) [13,34] is also zero, since there is no excited magnetic dipole moment m=0 for an ideal electric-dipole scatterer. In this case, the extinction of helicity from the incoming beam W H can be calculated as a projection of the induced electric dipole moment on the magnetic focal field W H ∝− p · H ψ * foc (r 0 ) [13].…”

Section: Theorymentioning

confidence: 99%

“…Lastly, it is remarkable that the scattered helicity ∝ (p · m * ) [13,34] is also zero, since there is no excited magnetic dipole moment m=0 for an ideal electric-dipole scatterer. In this case, the extinction of helicity from the incoming beam W H can be calculated as a projection of the induced electric dipole moment on the magnetic focal field W H ∝− p · H ψ * foc (r 0 ) [13]. On the one hand, substituting the expression for the dipole moment p, we get W H ∝ a 1 E ψ foc (r 0 ) · H ψ * foc (r 0 ) , which resembles the definition of the helicity density of the focal fields K ψ foc modified by the Mie coefficient a 1 .…”

Section: Theorymentioning

confidence: 99%

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Mimicking chiral light-matter interaction

Nechayev

Banzer

2019

Phys. Rev. B

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We demonstrate that electric-dipole scatterers can mimic chiral light-matter interaction by generating far-field circular polarization upon scattering, even though the optical chirality of the incident field as well as that of the scattered light is zero. The presented effect originates from the fact that electric-dipole scatterers respond selectively only to the incident electric field, which eventually results in depolarization of the transmitted beam and in generation of far-field circular polarization. To experimentally demonstrate this effect we utilize a cylindrical vector beam with spiral polarization and a spherical gold nanoparticle positioned on the optical axis -the axis of rotational symmetry of the system. Our experiment and a simple theoretical model address the fundamentals of duality symmetry in optics and chiral light-matter interactions, accentuating their richness and ubiquity yet in highly symmetric configurations.

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Magnetoelectric‐Field Electrodynamics: Search for Magnetoelectric Point Scatterers

Kamenetskii

2022

Annalen der Physik

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Resonant scattering of electromagnetic (EM) waves by small particles is considered as one of the basic problems in metamaterial science. At present, special subwavelength resonators are considered as structural elements in chiral and bianisotropic metamaterials. There is a general consensus that these small scatterers behave like "artificial atoms" with strong electrical and magnetic responses and an interconnection between these responses. However, the observed effect of magnetoelectric (ME) coupling in these meta-atoms is not associated with the near-field manipulation properties caused by intrinsic magnetoelectricity. This arises the question whether ME point scatterers of EM radiation really exist. In this paper, we show that there are mesoscopic structures with electric and magnetic dipole-carrying excitations that behave like point scatterers with their inherent magnetoelectricity. In such subwavelength resonators, coherent oscillations of the electric polarization and magnetization can be considered as quasistatic oscillations described by electrostatic (ES) and magnetostatic (MS) scalar wave functions. The ME resonance effect arises from the coupling of two, ES and MS, oscillations. The near fields of these resonators, called the ME near fields, are characterized by simultaneous violation of time reversal and inversion symmetry. In study of ME fields and EM problems associated with these fields, we put forward the concept of ME-field electrodynamics.

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Optical theorem for the conservation of electromagnetic helicity: Significance for molecular energy transfer and enantiomeric discrimination by circular dichroism

Cited by 64 publications

References 43 publications

Orbital-to-spin angular momentum conversion employing local helicity

Orbital-to-spin angular momentum conversion employing local helicity

Mimicking chiral light-matter interaction

Magnetoelectric‐Field Electrodynamics: Search for Magnetoelectric Point Scatterers

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