Calculation of electromagnetic scattering by a large chiral sphere

Wu, Zhensen; Shang, Qingchao; Li, Zhengjun

doi:10.1364/ao.51.006661

Cited by 45 publications

(23 citation statements)

References 35 publications

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“…To this end, the condition we now apply is an approximation based on the physical case of a molecule that is essentially isotropic, yet chiral. (The study of notionally chiral spheres is a subject that has itself attracted recent interest [24][25][26][27].) Applying this assumption means that we can write G g, α a, G α 3ag, α α 3a 2 , G αα 9a 2 g, α αα 9a 3 , G ααα 27a 3 g, α ααα 27a 4 , where a and g are isotropic electric-electric and electricmagnetic scattering scalars, respectively.…”

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confidence: 99%

Laser optical separation of chiral molecules

Bradshaw

Andrews

2015

Opt. Lett.

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The optical trapping of molecules with an off-resonant laser beam involves a forward-Rayleigh scattering mechanism. It is shown that discriminatory effects arise on irradiating chiral molecules with circularly polarized light; the complete representation requires ensemble-weighted averaging to account for the influence of the trapping beam on the distribution of molecular orientations. Results of general application enable comparisons to be drawn between the results for two limits of the input laser intensity. It emerges that, in a racemic mixture, there is a differential driving force whose effect, at high laser intensities, is to produce differing local concentrations of the two enantiomers. Trapping of this type usually relates to the interaction of the laser field with a transition electric dipole, as shown by Fig. 1(a). Interactions between the irradiating beam and a transition magnetic dipole are also possible, but the associated coupling strength is usually much smaller in magnitude, and the effects are generally ignored. However, when considering the possibility of chiral discrimination (in which input light of left-handed circular polarization offers different observables compared to right-handed polarization), the conventional trapping mechanism involving only electric dipole transition moments has to be extended to accommodate transition magnetic dipoles [7]. In fact, the forward-Rayleigh scattering events most relevant in chiral discrimination involve a mixture of magnetic and electric dipole interactions, as illustrated by Fig. 1(b), with one kind of coupling involved in the input photon annihilation and the other in the output photon release.To understand the energetics in greater detail, we note that the underlying mechanism for the optical trapping of molecules is based on the variation of intensity within the optical beam, which produces a position-dependent lowering of energy for the molecules it encounters: the alternating electric field of the radiation may be interpreted as producing a dynamic Stark shift to the molecular ground state energy. In terms of quantum electrodynamics, the energy shift (which is quadratically dependent on the electric field of the light) has to originate in forward-Rayleigh scattering, i.e., the concerted annihilation and creation of photons with identical energy and wave-vector. In such a case, the optical wavelengths will lie in a region of transparency for the irradiated molecule-the throughput laser beam therefore emerges unchanged. The primary physical determinant of optical trapping is the potential energy U, whose evaluation from quantum theory requires that the initial and final states (here denoted by I) are identical [8]. An expression for U per molecule is determined from second-order time-dependent perturbation theory, i.e.,where S is an intermediate state of the system comprising both molecule and radiation, E is the energy of the state denoted by its subscript, and H int is the dipolar interaction Hamiltonian given byHere, μ and m are the electric and...

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confidence: 99%

Laser optical separation of chiral molecules

Bradshaw

Andrews

2015

Opt. Lett.

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“…It becomes even trickier when considering droplets. In particular, scattering of light by a chiral particle is an issue that has started to be addressed only recently [14,15]. Moreover, Maxwell stress tensor formalism for inhomogeneous, chiral, and anisotropic optical media should be included as well as possible light-induced deformation of the shape of the droplet [16].…”

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Spin Controlled Optical Radiation Pressure

Tkachenko

Brasselet

2013

Phys. Rev. Lett.

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International audienceWe report on the full control of the optical radiation pressure at fixed photon flux and incident angle by the photon spin. This is done by using transparent chiral liquid crystal droplets that enable a strong coupling between the linear and angular degrees of freedom of a light field. From these results, we anticipate optical sorting of particles with different chirality as well as novel optical trapping and micromanipulation strategies

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“…Shang et al studied the radiation force on a chiral sphere for Gaussian beam incidence [118]. Electromagnetic scattering by a chiral sphere was also considered by Wu et al [119], and by Zhu et al [110]. Wang et al [125].…”

Section: Glmts For Non-spherical and Spherical Non-homogeneous Particmentioning

confidence: 99%