Symmetry and the generation and measurement of optical torque

Nieminen, Timo A.; Asavei, Theodor; Loke, Vincent L. Y.; Heckenberg, N. R.; Rubinsztein‐Dunlop, Halina

doi:10.1016/j.jqsrt.2009.03.013

Cited by 45 publications

(36 citation statements)

References 83 publications

(110 reference statements)

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“…A clear change in the angular momentum is seen, with a large transfer of power from the LG 0,−2 mode to the LG 0,0 , as expected from the second-order rotational symmetry of the rod. 27 There is also a 37% loss in total power, probably due to reflection from the glass rod or the conversion of the transmitted light into higher order modes.…”

Section: Resultsmentioning

confidence: 99%

“…31,32 Instead, it is necessary to consider the total angular momentum carried by the beam. 27 Instead of describing the beam as a superposition of left and right circularly polarized components with ±h spin per photon, and orbital modes with azimuthal phase variation exp(i φ and h orbital angular momentum, the beam can be written as a superposition of TE and TM vector spherical wavefunction (VSWF), or multipole, modes, M nm and N nm , as…”

Section: Indirect Measurement Of Orbital Angular Momentummentioning

confidence: 99%

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Measurement of angular momentum flux in optical tweezers

et al. 2011

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It is well established that a light beam can carry angular momentum and therefore when using optical tweezers it is possible to exert torques to twist or rotate microscopic objects. Both spin and orbital angular momentum can be transferred. This transfer can be achieved using birefringent particles exposed to a Gaussian circularly polarized beam. In this case, a transfer of spin angular momentum will occur. The change in spin, and hence the torque, can be readily measured optically. On the other hand, it is much more challenging to measure orbital angular momentum and torque. Laguerre-Gauss mode decomposition, as used for orbital angular momentum encoding for quantum communication, and rotational frequency shift can be used, and are effective methods in a macro-environment. However, the situation becomes more complicated when a measurement is done on microscale, especially with highly focused laser beams. We review the methods for the measurement of the angular momentum of light in optical tweezers, and the challenges faced when measuring orbital angular momentum. We also demonstrate one possible simple method for a quantitative measurement of the orbital angular momentum in optical tweezers.

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Section: Resultsmentioning

confidence: 99%

Section: Indirect Measurement Of Orbital Angular Momentummentioning

confidence: 99%

Measurement of angular momentum flux in optical tweezers

et al. 2011

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“…For rotating particles, the fit of ACFs with equation 3 gives a direct measurement of the particle rotational frequency, O, which is used to evaluate the averaged optical torque transferred to the trapped particle. As O is set by the equilibrium between optical and rotational drag torques 43 , the optical torque modulus, G þ rad , is equal to the rotational drag torque on a sphere rotating in a fluid at low Reynolds number 10 , G drag ¼ 8pZR 3 0 O. Note that we also monitor the particle dynamics in the trap by video microscopy (Supplementary Movies 1 and 2) so that we can verify the absence of tumbling and the uniform rotation about the light propagation (z À ) axis.…”

Section: Chiral Microparticlesmentioning

confidence: 99%

Polarization-dependent optomechanics mediated by chiral microresonators

et al. 2014

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Chirality is one of the most prominent and intriguing aspects of nature, from spiral galaxies down to aminoacids. Despite the wide range of living and non-living, natural and artificial chiral systems at different scales, the origin of chirality-induced phenomena is often puzzling. Here we assess the onset of chiral optomechanics, exploiting the control of the interaction between chiral entities. We perform an experimental and theoretical investigation of the simultaneous optical trapping and rotation of spherulite-like chiral microparticles. Due to their shell structure (Bragg dielectric resonator), the microparticles function as omnidirectional chiral mirrors yielding highly polarization-dependent optomechanical effects. The coupling of linear and angular momentum, mediated by the optical polarization and the microparticles chiral reflectance, allows for fine tuning of chirality-induced optical forces and torques. This offers tools for optomechanics, optical sorting and sensing and optofluidics.

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“…We fabricate microrotors using two-photon photopolymerization 9 and they are usually driven using LG 02 or LG 04 beams. The method we use to determine torque efficiency experimentally 10,11 involves measuring the rate of rotation and the change in circular polarization.…”

Section: The Microrotormentioning

confidence: 99%

Optimization of optically-driven micromachines

et al. 2009

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While a variety of different optically-driven micromachines have been demonstrated by a number of groups around the world, there is a striking similarity in the designs used. The typical optically-driven rotor consists of a number of arms attached to a central hub, or elongated stalk in the case of free-floating rotors. This is a consequence of the relationship between the symmetry of a scattering object and the transfer of optical angular momentum from a beam to the object.We use a hybrid discrete-dipole approximation/T-matrix method algorithm to computationally model the scattering by such optically-driven rotors. We systematically explore the effects of the most important parameters of rotors, such as the thickness, length, and width of the arms, in order to maximize the torque efficiency.We show that it is possible to use computational modelling to optimize the design of such devices. We also compare the computational results with experiment.

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Symmetry and the generation and measurement of optical torque

Cited by 45 publications

References 83 publications

Measurement of angular momentum flux in optical tweezers

Measurement of angular momentum flux in optical tweezers

Polarization-dependent optomechanics mediated by chiral microresonators

Optimization of optically-driven micromachines

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