Observation of the Transfer of the Local Angular Momentum Density of a Multiringed Light Beam to an Optically Trapped Particle

Garcés-Chávez, V.; McGloin, David; Padgett, Miles J.; Dultz, W.; Schmitzer, Heidrun; Dholakia, Kishan

doi:10.1103/physrevlett.91.093602

Cited by 331 publications

(240 citation statements)

References 16 publications

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“…In particular, the orbital and spinning motions of probe particles in circularly-polarized vortex beams [15][16][17][18] originate exactly due to the force from the azimuthal component of p O and the torque from the longitudinal component of the spin density s. Furthermore, the quantum-mechanical resonant momentum transfer from light to a two-level atom is also determined by the canonical momentum density 37,38 . Finally, a remarkable recent experiment 36 , which realized quantum weak measurements of the local momentum of photons, also measured p O (ref.…”

Section: Resultsmentioning

confidence: 99%

“…At the same time, the spin s is proportional to the polarization helicity s and is also collinear with the wave vector. The optical momentum and spin densities can be measured experimentally by placing a small absorbing particle in the field and observing its linear and spinning motion [15][16][17][18][19] . Naturally, the radiation force and torque (with respect to the particle's centre) quantify the momentum and AM transfer to the particle and are proportional to the densities (2) in the plane wave (1): Fpp and Tps (refs 19-25), Fig.…”

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confidence: 99%

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Extraordinary momentum and spin in evanescent waves

2014

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Momentum and spin represent fundamental dynamic properties of quantum particles and fields. In particular, propagating optical waves (photons) carry momentum and longitudinal spin determined by the wave vector and circular polarization, respectively. Here we show that exactly the opposite can be the case for evanescent optical waves. A single evanescent wave possesses a spin component, which is independent of the polarization and is orthogonal to the wave vector. Furthermore, such a wave carries a momentum component, which is determined by the circular polarization and is also orthogonal to the wave vector. We show that these extraordinary properties reveal a fundamental Belinfante's spin momentum, known in field theory and unobservable in propagating fields. We demonstrate that the transverse momentum and spin push and twist a probe Mie particle in an evanescent field. This allows the observation of 'impossible' properties of light and of a fundamental field-theory quantity, which was previously considered as 'virtual'.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Extraordinary momentum and spin in evanescent waves

2014

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“…Recently, experimentalists [13,14] showed that the spin and orbital AM of a non-paraxial beam play distinct roles in the interaction with microscopic birefringent particles trapped off the beam axis in optical tweezers. It was observed [14] that the spin of light makes the particle rotate around its own axis and the orbital AM makes the particle rotate around the beam's axis.…”

Section: Introductionmentioning

confidence: 99%

Spin and orbital angular momentum of a class of nonparaxial light beams having a globally defined polarization

2009

Phys. Rev. A

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It is shown that the momentum density of free electromagnetic field splits into two parts. One has no contribution to the net momentum due to the transversality condition. The other yields all the momentum. The angular momentum that is associated with the former part is spin, and the angular momentum that is associated with the latter part is orbital angular momentum. Expressions for the spin and orbital angular momentum are given in terms of the electric vector in reciprocal space. The spin and orbital angular momentum defined this way are used to investigate the angular momentum of nonparaxial beams that are described in a recently published paper [Phys. Rev. A 78, 063831 (2008)]. It is found that the orbital angular momentum depends, apart from an l-dependent term, on two global quantities, the polarization represented by a generalized Jones vector and a new characteristic represented by a unit vector I, though the spin depends only on the polarization. The polarization dependence of orbital angular momentum through the impact of I is obtained and discussed. Some applications of the result obtained here are also made. The fact that the spin originates from the momentum density that has no contribution to the net momentum is used to show that there does not exist the paradox on the spin of circularly polarized plane wave. The polarization dependence of both spin and orbital angular momentum is shown to be the origin of conversion from the spin of a paraxial Laguerre-Gaussian beam into the orbital angular momentum of the focused beam through a high numerical aperture.

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“…This is accompanied by a steady improvement in particle manipulation techniques and theories [8][9][10][11][12][13][14], and by the use of spatially structured waves [15] with enhanced helicity [16] to increase the signal in circular dichroism [17,18] for enantiomeric discrimination [19][20][21]. In addition, recent studies [22] in fluorescence resonance energy transfer (FRET) [23,24], (see also [25,26]), show an electromagnetic force between excited molecules, different from the Van der Waals force when they are in their ground-state.…”

Section: Introductionmentioning

confidence: 99%

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

Nieto‐Vesperinas¹

2015

Phys. Rev. A

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We put forward the physical meaning of the conservation equation for the helicity on scattering of an electromagnetic field with a generally magnetodielectric bi-isotropic dipolar object. This is the optical theorem for the helicity that, as we find, plays a role for this quantity analogous to that of the optical theorem for energy. We discuss its consequences for helicity transfer between molecules and for new detection procedures of circular dichroism based on ellipsometric measurements.

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Observation of the Transfer of the Local Angular Momentum Density of a Multiringed Light Beam to an Optically Trapped Particle

Cited by 331 publications

References 16 publications

Extraordinary momentum and spin in evanescent waves

Extraordinary momentum and spin in evanescent waves

Spin and orbital angular momentum of a class of nonparaxial light beams having a globally defined polarization

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

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