Optical Motion Control Applied to the Atmospheric Cloud Physics Laboratory (ACPL)

Eaton, L. R.; Neste, S. L.

doi:10.2514/3.61110

Cited by 3 publications

(2 citation statements)

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“…It is very difficult to estimate the magnitude of possible thermal effects like the photophoretic forces known to act on illuminated particles in air [12], but they could be expected to be smaller in our experiments because of the much higher thermal conductivities of the liquid media and the particles used. We have been unable to find any reports of such forces in liquids.…”

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confidence: 97%

Direct Observation of Transfer of Angular Momentum to Absorptive Particles from a Laser Beam with a Phase Singularity

et al. 1995

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manuscript received pri r rejective articles can be trappe in t e ar d h dark central minimum of a doughnut laser beam d h 1 ram. Such beams carry angular momentum ed usin a hi h efficiency computer generate o ogram. uc d ith the central phase singularity even when linearly due to the h helical wave-front structure associate wit t e cen ra b tion of this angular momentum transferred polarized. rapp Tra ed abso tive particles spin due to a sorp ion o an be reversed b changing the sign of the singularity. from the singularity beam. The direction of spin can e reverse y c a PACS numbers: 42.25.Md, 42.40.My It is well known that a circularly polarized beam carries angular momentum. Each photon of such a beam has the optical angular momentum are hard to observe in most circumstances as they represent extremely small quantities. The angular momentum flux carried by a circularly polarized 10 mW He-Ne laser beam is of the order of 10-18 mN. The first attempt to measure the torque produced by the optical angular momentum was made b B h [1] 59 years ago. Beth reported that his results agreed with theory in sign and magnitude. More recent y Santamato et al. [2] observed the light induced rotation of liquid crystal molecules, Chang and Lee [3] calculated the optical torque acting on a weakly absorbing optically levitated sphere, and Ashkin and Dziedzic [4] observed rotation of particles optically levitated in air.A linearly polarized wave containing a central phase singularity also carries angular momentum associated with its helical structure. Figure 1 shows this structure for a TEMot beam [5]. Each photon carries I Tt angular momentum where l is called the topological charge of the singularity. This contribution to the angular momentum is sometimes referred to as "orbital angular momentum" to d h t f om "spin" angular momentum associated aistinguis i ro with circular polarization [6,7]. Allen et al. [6] have proposed to measure the angular momentum carried by a doughnut laser beam by measuring the torque acting on an optical device which reverses the chirality of the beam. We have demonstrated in a previous paper [8] that black or rejective particles of sizes of 1 -2 p, m can be trapped optically in a liquid by higher order doughnuts produced by high efficiency computer generated holograms. We also mentioned that some bigger absorptive particles were set into rotation by slightly defocused doughnuts.In this paper we report on further experiments concerned with the transfer of angular momentum to absorptive particles and their subsequent rotation. The detection is performed using a video camera. A large number of small particles have been trapped and have been recorded. Our results clearly show that the rotation directions of all these trapped particles agree with the sign of the doughnut.In this Letter we analyze the results of the rotating particles in terms of possible torques acting on a trapped absorptive particle. ! / f ofa TEM qr, tu e e e (~" t" ' '"'] beam containing a first order phase singularity. FIG. 1. Snapsho...

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Direct Observation of Transfer of Angular Momentum to Absorptive Particles from a Laser Beam with a Phase Singularity

et al. 1995

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“…The angular momentum flux carried by a circularly polarized 10 mW He-Ne laser beam is of the order of [10][11][12][13][14][15][16][17][18] A linearly polarized wave containing a central phase singularity also carries angular momentum associated with its helical structure. Figure 1 shows this structure for a TEMot beam [5].…”

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Direct observation of transfer of angular momentum to absorptive particles from a laser beam with a phase singularity

He¹,

Friese²,

Heckenberg³

et al.

Optical Angular Momentum

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Applications of Laser Radiation Pressure

Ashkin¹

1980

Science

576

281

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Use of lasers has revolutionized the study and applications of radiation pressure. Light forces have been achieved which strongly affect the dynamics of individual small particles. It is now possible to optically accelerate, slow, stably trap, and manipulate micrometer-sized dielectric particles and atoms. This leads to a diversity of new scientific and practical applications in fields where small particles play a role, such as light scattering, cloud physics, aerosol science, atomic physics, quantum optics, and high-resolution spectroscopy.

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Optical Motion Control Applied to the Atmospheric Cloud Physics Laboratory (ACPL)

Cited by 3 publications

References 4 publications

Direct Observation of Transfer of Angular Momentum to Absorptive Particles from a Laser Beam with a Phase Singularity

Direct Observation of Transfer of Angular Momentum to Absorptive Particles from a Laser Beam with a Phase Singularity

Direct observation of transfer of angular momentum to absorptive particles from a laser beam with a phase singularity

Applications of Laser Radiation Pressure

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