176 research outputs found
Photophoretic manipulation of absorbing aerosol particles with vortex beams: theory versus experiment
We develop a theoretical approach for describing the optical trapping and manipulation of carbon nanoclusters in air with a dual-vortex optical trap, as realized recently in experiment [V. Shvedov et al., Opt. Express 17, 5743 (2009)]. We calculate both longitudinal and transverse
photophoretic forces acting on a spherical absorbing particle, and then compare our theoretical predictions with the experimental data
Momentum transfer in a standing optical vortex
A field superposition of singular beams incident on, and then reflected from
a mirror has been investigated. It was demonstrated that the standing optical
wave, which contains a vortex, possesses an orbital angle momentum where the
energy flux circulates only in the azimuth direction of the beam. We show in
this paper that the standing light wave containing the optical vortex transfers
angular momentum to a substance located in the field of the vortex without
moving the substance in the azimuth or radial directions. This property of the
standing vortex present an opportunity to form the three-dimensional optical
traps, gasdynamic and hydrodynamic vortices, in a localised volume by a direct
transfer of the orbital angular momentum from the optical vortex.Comment: English has been corrected; a second address entered; Eq.(13) and
(14) corrected. 11 pages, including 1 figur
Exponentially Large Probabilities in Quantum Gravity
The problem of topology change transitions in quantum gravity is investigated
from the Wheeler-de Witt wave function point of view. It is argued that for all
theories allowing wormhole effects the wave function of the universe is
exponentially large. If the wormhole action is positive, one can try to
overcome this difficulty by redefinition of the inner product, while for the
case of negative wormhole action the more serious problems arise.Comment: 9 pages in LaTeX, 4 figures in PostScript, the brief version of this
paper is to appear in Proceedings of the XXIV ITEP Winter School of Physic
Renormalization of Poincare Transformations in Hamiltonian Semiclassical Field Theory
Semiclassical Hamiltonian field theory is investigated from the axiomatic
point of view. A notion of a semiclassical state is introduced. An "elementary"
semiclassical state is specified by a set of classical field configuration and
quantum state in this external field. "Composed" semiclassical states viewed as
formal superpositions of "elementary" states are nontrivial only if the Maslov
isotropic condition is satisfied; the inner product of "composed" semiclassical
states is degenerate. The mathematical proof of Poincare invariance of
semiclassical field theory is obtained for "elementary" and "composed"
semiclassical states. The notion of semiclassical field is introduced; its
Poincare invariance is also mathematically proved.Comment: LaTeX, 40 pages; short version of hep-th/010307
Optical guiding of absorbing nanoclusters in air
We suggest a novel approach in all-optical trapping employing
a photophoretic force for manipulation of absorbing particles in open air.
We demonstrate experimentally the robust three-dimensional guiding, over
the distances of a few millimeters, of agglomerates of carbon nanoparticles
with the size spanned from 100 nm to 10μm, as well as their acceleration
up to velocities of 1 cm/sec. We achieve stable positioning and guiding of
particles as well as simultaneous trapping of a large number of particles in a
dual beam optical trap created by two counter-propagating and co-rotating
optical vortex beams
Selective trapping of multiple particles by volume speckle field
We suggest a new approach for selective trapping of light
absorbing particles in gases by multiple optical bottle-beam-like traps
created by volume speckle field. We demonstrate stable simultaneous
confinement of a few thousand micro-particles in air with a single lowpower
laser beam. The size distribution of trapped particles exhibits a
narrow peak near the average size of an optical speckle. Thus, the speckleformed
traps act as a sieve with the holes selecting particles of a similar size
Generation of optical bottle beams by incoherent white-light vortices
We generate experimentally optical bottle beams from incoherent
double-charge white-light vortices, and show that their parameters can
be efficiently controlled by varying the beam focusing conditions
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