Spin-to-orbital angular momentum conversion in focusing, scattering, and imaging systems

Bliokh, Konstantin Y.; Ostrovskaya, Elena A.; Alonso, Miguel A.; Rodríguez-Herrera, Oscar G.; Lara, David; Dainty, Chris

doi:10.1364/oe.19.026132

Cited by 255 publications

(221 citation statements)

References 54 publications

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“…This contradicts numerous observable SOI effects (spin-dependent orbital characteristics), known for both electron [9,[39][40][41][43][44][45][46]62] and optical (photon) [24,25,[47][48][49][50][51][52][53] fields. …”

Section: B Newton-wigner-foldy-wouthuysen Operatorsmentioning

confidence: 82%

Position, spin, and orbital angular momentum of a relativistic electron

2017

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Motivated by recent interest in relativistic electron vortex states, we revisit the spin and orbital angular momentum properties of Dirac electrons. These are uniquely determined by the choice of the position operator for a relativistic electron. We consider two main approaches discussed in the literature: (i) the projection of operators onto the positive-energy subspace, which removes the Zitterbewegung effects and correctly describes spin-orbit interaction effects, and (ii) the use of Newton-Wigner-Foldy-Wouthuysen operators based on the inverse Foldy-Wouthuysen transformation. We argue that the first approach [previously described in application to Dirac vortex beams in K. Y. Bliokh et al., Phys. Rev. Lett. 107, 174802 (2011)] has a more natural physical interpretation, including spin-orbit interactions and a nonsingular zero-mass limit, than the second one [S. M.

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Section: B Newton-wigner-foldy-wouthuysen Operatorsmentioning

confidence: 82%

Position, spin, and orbital angular momentum of a relativistic electron

2017

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“…However, although perfect duality symmetry is impossible to achieve without such a material, some systems can be designed in such a way that helicity is preserved to a very good approximation. 13,14 In particular, microscope objectives designed to fulfill the aplanatic lens model do not change the helicity of light: 2,15 an effectively dual response is restored by special antireflection coatings. The following key outcomes make the experimental handling of helicity simple: (i) helicity can be manipulated and measured for collimated light beams through the polarization of the field; and (ii) using microscope objectives, transformation between paraxial and non-paraxial regimes without changing the helicity content is possible.…”

Section: Methodsmentioning

confidence: 99%

Experimental control of optical helicity in nanophotonics

et al. 2014

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An analysis of light-matter interactions based on symmetries can provide valuable insight, particularly because it reveals which quantities are conserved and which ones can be transformed within a physical system. In this context, helicity can be a useful addition to more commonly considered observables such as angular momentum. The question arises how to treat helicity, the projection of the total angular momentum onto the linear momentum direction, in practical experiments. In this paper, we put forward a simple but versatile experimental treatment of helicity. We then apply the proposed method to the scattering of light by isolated cylindrical nanoapertures in a gold film. This allows us to study the helicity transformation taking place during the interaction of focused light with the nanoapertures. In particular, we observe from the transmitted light that the scaling of the helicity transformed component with the aperture size is very different to the direct helicity component.

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“…A remarkable SOI effect is the generation of optical vortices from circularly polarized beams, a process accompanied by spin to orbital angular momentum conversion. Standard procedures to achieve vortex generation are focusing by high-numerical aperture lens [2,3], scattering by small particles [3], propagation along the optical axis of a uniaxial crystal [4,5] and propagation through semiconductor microcavities [6]. Similar SOI effects involving Bessel beams have been considered in uniaxial crystals [7] and at reflection and transmission by a planar interface between two homogeneous media [8].…”

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Efficient Vortex Generation in Subwavelength Epsilon-Near-Zero Slabs

Ciattoni¹,

Marini

Rizza³

2017

Phys. Rev. Lett.

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We show that a homogeneous and isotropic slab, illuminated by a circularly polarized beam with no topological charge, produces vortices of order two in the opposite circularly polarized components of the reflected and transmitted fields, as a consequence of the difference between transverse magnetic and transverse electric dynamics. In the epsilon-near-zero regime, we find that vortex generation is remarkably efficient in sub-wavelength thick slabs up to the paraxial regime. This physically stems from the fact that a vacuum paraxial field can excite a nonparaxial field inside an epsilon-near-zero slab since it hosts slowly varying fields over physically large portion of the bulk. Our theoretical predictions indicate that epsilon-near-zero media hold great potential as nanophotonic elements for manipulating the angular momentum of the radiation, since they are available without resorting to complicated micro/nano fabrication processes and can operate even at very small (ultraviolet) wavelengths.Spin-orbit interaction (SOI) of light is a very important research topic since it provides a tool for manipulating the spatial degrees of freedom of the radiation by acting on its circular polarization state [1]. A remarkable SOI effect is the generation of optical vortices from circularly polarized beams, a process accompanied by spin to orbital angular momentum conversion. Standard procedures to achieve vortex generation are focusing by high-numerical aperture lens [2,3], scattering by small particles [3], propagation along the optical axis of a uniaxial crystal [4,5] and propagation through semiconductor microcavities [6]. Similar SOI effects involving Bessel beams have been considered in uniaxial crystals [7] and at reflection and transmission by a planar interface between two homogeneous media [8]. The advent of metamaterials has further increased the SOI research effort [9], mostly in the use of ultra-thin metasurfaces for manipulating the angular momentum of light [10,11] and for vortex generation [12,13].Epsilon near zero (ENZ) media are nowadays attracting an increasing research interest due to the very unconventional way they affect the electromagnetic radiation. The effective wavelength in ENZ media is much larger than the vacuum wavelength and this entails a regime quite opposite to geometrical optics where the field is slowly-varying over relatively large portions of the bulk. Such feature has been exploited for squeezing electromagnetic waves at will [14], for tailoring the antenna radiation pattern [15] and for enhancing nonlinear response of matter [16][17][18][19][20]. In the context of light SOI, it has recently been proposed that a thin epsilon-near-zero slab can enhance the spin Hall effect of transmitted light [21].In this letter we show that a homogeneous, isotropic and ultra-thin (sub-wavelength thick) slab can support vortex generation. We prove that such genuine SOI effect is physically due to the mutual difference between the dynamics of transverse magnetic and transverse electric fields upon refl...

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Spin-to-orbital angular momentum conversion in focusing, scattering, and imaging systems

Cited by 255 publications

References 54 publications

Position, spin, and orbital angular momentum of a relativistic electron

Position, spin, and orbital angular momentum of a relativistic electron

Experimental control of optical helicity in nanophotonics

Efficient Vortex Generation in Subwavelength Epsilon-Near-Zero Slabs

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