Negative Optical Torque

Chen, Jun; Ng, Jack; Ding, Kun; Fung, Kin Hung; Lin, Zhifang; Chan, Che Ting

doi:10.1038/srep06386

Cited by 67 publications

(62 citation statements)

References 42 publications

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“…These equations are seen to be compatible with (33), (36), (58) and (59). Hence, in contrast with some previous work [27][28][29][30][31][32][33] and in agreement with some experiments and calculations [22, 24-26, 34, 36, 38], these equations show that this particle does not experiences a torque and spins due to the so far called intrinsic torque: < Γ 0 >, [which, as we have just seen, is cancelled by a part of the recoil torque on this kind of particles through the optical theorem relating imaginary parts and moduli of the permittivities, Eq.…”

Section: The Total Electromagnetic Torquesupporting

confidence: 62%

“…< Γ 0 > is the extinction electromagnetic torque, analogous to the extinction energy in the optical theorem [36,54,70],…”

Section: Incident Plane Wavementioning

confidence: 99%

“…Observations are more difficult to control and to quantitatively interpret with existing models. With few exceptions [34,36], most experimental [27,28] and theoretical [29][30][31][32][33][34]53] studies employ a static formulation, (perhaps following the path of pioneering work [21]), which was shown [37] to be incomplete and not compatible with energy and angular momentum conservation. Only for extremely small (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Optical torque: Electromagnetic spin and orbital-angular-momentum conservation laws and their significance

Nieto‐Vesperinas

2015

Phys. Rev. A

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The physics involved in the fundamental conservation equations of the spin and orbital angular momenta leads to new laws and phenomena that are disclosed here. To this end, we analyse the scattering of an electromagnetic wavefield by the canonical system constituted by a small particle, which is assumed dipolar in the wide sense. Specifically, under quite general conditions these laws lead to understanding the contribution and weight of each of those angular momenta to the electromagnetic torque exerted by the field on the object, which is shown to consist of an extinction and a scattering, or recoil, part. This leads to an interpretation of its effect different to that taken up till now by many theoretical and experimental works, and implies that a part of the recoil torque cancels the usually called intrinsic torque which was often considered responsible of the particle spinning. In addition, we obtain the contribution of the spatial structure of the wave to this torque, unknown to this date, showing its effect in the orbiting of the object, and demonstrating that it often leads to a negative torque on a single particle, i.e. opposite to the incident helicity, producing an orbital motion contrary to its spinning. Furthermore, we establish a decomposition of the electromagnetic torque into conservative and non-conservative components in which the helicity and the spin angular momentum play a role analogous to the energy and its flux for electromagnetic forces. These phenomena are illustrated with examples of beams, also showing the difficulties of some paraxial formulations whose fields do not hold the transversality condition.

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Section: The Total Electromagnetic Torquesupporting

confidence: 62%

“…< Γ 0 > is the extinction electromagnetic torque, analogous to the extinction energy in the optical theorem [36,54,70],…”

Section: Incident Plane Wavementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optical torque: Electromagnetic spin and orbital-angular-momentum conservation laws and their significance

Nieto‐Vesperinas

2015

Phys. Rev. A

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“…On the other hand, when the incident light carries only SAM or has no angular momentum to begin with, the twist needs to be provided by the optical response of the object; for example, the intrinsic [18][19][20] and mimicked [21] anisotropy of the material, as well as the asymmetry of the structure, such as chirality or structural windmill effects [22][23][24][25]. Very recently, it has also been theoretically predicted that light can exert "negative optical torque" on aggregates of dielectric microspheres [26].…”

Section: Introductionmentioning

confidence: 99%

Optical torque from enhanced scattering by multipolar plasmonic resonance

Lee

Fung²,

Jin

et al. 2014

Nanophotonics

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Abstract:We present a theoretical study of the optical angular momentum transfer from a circularly polarized plane wave to thin metal nanoparticles of different rotational symmetries. While absorption has been regarded as the predominant mechanism of torque generation on the nanoscale, we demonstrate numerically how the contribution from scattering can be enhanced by using multipolar plasmon resonance. The multipolar modes in non-circular particles can convert the angular momentum carried by the scattered field and thereby produce scattering-dominant optical torque, while a circularly symmetric particle cannot. Our results show that the optical torque induced by resonant scattering can contribute to 80% of the total optical torque in gold particles. This scattering-dominant torque generation is extremely mode-specific, and deserves to be distinguished from the absorption-dominant mechanism. Our findings might have applications in optical manipulation on the nanoscale as well as new designs in plasmonics and metamaterials.

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“…It also generates individual vortices in the (lateral) plane perpendicular to the axis of wave propagation corresponding to a cross-section of the incident nondiffracting beam [19]. This specific feature provides the impetus to analyze the optical radiation spin torque exerted on a small dielectric absorptive sphere from the standpoint of the counter-intuitive "negative" optical radiation torque generation, meaning that the sphere would rotate around its center of mass in opposite handedness of the beam's angular momentum [24]. Note that this phenomenon has been originally observed from the standpoint of acoustical radiation spin torque theory using Bessel vortex beams [25].…”

mentioning

confidence: 99%

Negative optical spin torque wrench of a non-diffracting non-paraxial fractional Bessel vortex beam

Mitri

2016

Journal of Quantitative Spectroscopy and Radiative Transfer

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-An absorptive Rayleigh dielectric sphere in a non-diffracting non-paraxial fractional Bessel vortex beam experiences a spin torque. The axial and transverse radiation spin torque components are evaluated in the dipole approximation using the radiative correction of the electric field. Particular emphasis is given on the polarization as well as changing the topological charge  and the beam's half-cone angle. When  is zero, the axial spin torque component vanishes. However, when  becomes a real positive number, the vortex beam induces left-handed (negative) axial spin torque as the sphere shifts off-axially from the center of the beam. The results show that a non-diffracting non-paraxial fractional Bessel vortex beam is capable to induce a spin reversal of an absorptive Rayleigh sphere placed arbitrarily in its path. Potential applications are yet to be explored in particle manipulation, rotation in optical tweezers, optical tractor beams, the design of optically-engineered metamaterials to name a few areas. Keywords: Negative spin torque, dielectric sphere, dipole approximation.The optical radiation torque [1] which arises from the transfer of angular momentum of light to a (lossy) dielectric sphere has received significant attention in optical levitation [2-4] and particle rotation applications in atomic physics [5,6], cell biology [7] and other areas [8,9]. In common optical laser beams, and under some conditions related to the particle absorptive properties, a spin torque causing the particle to rotate around its center of mass arises, in addition to an orbital component causing the particle to rotate around the beam's axis of wave propagation [1]. Note that the orbital torque component exerted on the sphere vanishes at the center of the beam. Moreover, the sphere should be absorptive in order to experience a spin torque [1]. Various standard types of laser beams have been suggested and investigated for this purpose [10,11]. Examples of beams also include optical vortices of Gaussian-like [12,13] and nondiffracting beams [14].A particular kind of vortices with fractional topological charge (or order) has received increasing attention due to their special In contrast, another class for factional vortex beams (which can be realized experimentally using blazed-phase hologram encoded in a programmable liquid crystal display illuminated with a He-Ne laser [19]) and displays limited-diffracting features during propagation exists [19,20]. The physically-realizable apodized beam carrying finite energy preserves the nondiffracting propagation property. It is also known as a high-order Bessel vortex beam of fractional type  (HOBVB-F) [21][22][23]. A HOBVB-F with fractional order  connects standard nondiffracting Bessel (vortex) beams (Fig. 1) of successive integer order in a smooth transition. It also generates individual vortices in the (lateral) plane perpendicular to the axis of wave propagation corresponding to a cross-section of the incident nondiffracting beam [19]. This specific feature provides ...

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Negative Optical Torque

Cited by 67 publications

References 42 publications

Optical torque: Electromagnetic spin and orbital-angular-momentum conservation laws and their significance

Optical torque: Electromagnetic spin and orbital-angular-momentum conservation laws and their significance

Optical torque from enhanced scattering by multipolar plasmonic resonance

Negative optical spin torque wrench of a non-diffracting non-paraxial fractional Bessel vortex beam

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