927 research outputs found
Optically bound microscopic particles in one dimension
Counter-propagating light fields have the ability to create self-organized
one-dimensional optically bound arrays of microscopic particles, where the
light fields adapt to the particle locations and vice versa. We develop a
theoretical model to describe this situation and show good agreement with
recent experimental data (Phys. Rev. Lett. 89, 128301 (2002)) for two and three
particles, if the scattering force is assumed to dominate the axial trapping of
the particles. The extension of these ideas to two and three dimensional
optically bound states is also discussed.Comment: 12 pages, incl. 5 figures, accepted by Phys. Rev.
Coupled Dipole Method Determination of the Electromagnetic Force on a Particle over a Flat Dielectric Substrate
We present a theory to compute the force due to light upon a particle on a
dielectric plane by the Coupled Dipole Method (CDM). We show that, with this
procedure, two equivalent ways of analysis are possible, both based on
Maxwell's stress tensor. The interest in using this method is that the nature
and size or shape of the object, can be arbitrary. Even more, the presence of a
substrate can be incorporated. To validate our theory, we present an analytical
expression of the force due to the light acting on a particle either in
presence, or not, of a surface. The plane wave illuminating the sphere can be
either propagating or evanescent. Both two and three dimensional calculations
are studied.Comment: 10 pages, 8 figures and 3 table
Processing carbon nanotubes with holographic optical tweezers
We report the first demonstration that carbon nanotubes can be trapped and
manipulated by optical tweezers. This observation is surprising because
individual nanotubes are substantially smaller than the wavelength of light,
and thus should not be amenable to optical trapping. Even so, nanotube bundles,
and perhaps even individual nanotubes, can be transported at high speeds,
deposited onto substrates, untangled, and selectively ablated, all with visible
light. The use of holographic optical tweezers, capable of creating hundreds of
independent traps simultaneously, suggests opportunities for highly parallel
nanotube processing with light.Comment: 3 pages, 1 figur
Optical binding of particles with or without the presence of a flat dielectric surface
Optical fields can induce forces between microscopic objects, thus giving
rise to new structures of matter. We study theoretically these optical forces
between two spheres, either isolated in water, or in presence of a flat
dielectric surface. We observe different behavior in the binding force between
particles at large and at small distances (in comparison with the wavelength)
from each other. This is due to the great contribution of evanescent waves at
short distances. We analyze how the optical binding depends of the size of the
particles, the material composing them, the wavelength and, above all, on the
polarization of the incident beam. We also show that depending on the
polarization, the force between small particles at small distances changes its
sign. Finally, the presence of a substrate surface is analyzed showing that it
only slightly changes the magnitudes of the forces, but not their qualitative
nature, except when one employs total internal reflection, case in which the
particles are induced to move together along the surface.Comment: 8 pages, 9 figures, and 1 tabl
Selective nanomanipulation using optical forces
We present a detailed theoretical study of the recent proposal for selective
nanomanipulation of nanometric particles above a substrate using near-field
optical forces [Chaumet {\it et al.} Phys. Rev. Lett. {\bf 88}, 123601 (2002)].
Evanescent light scattering at the apex of an apertureless near-field probe is
used to create an optical trap. The position of the trap is controlled on a
nanometric scale via the probe and small objects can be selectively trapped and
manipulated. We discuss the influence of the geometry of the particles and the
probe on the efficiency of the trap. We also consider the influence of multiple
scattering among the particles on the substrate and its effect on the
robustness of the trap.Comment: 12 pages, 17 figure
Resonant radiation pressure on neutral particles in a waveguide
A theoretical analysis of electromagnetic forces on neutral particles in an
hollow waveguide is presented. We show that the effective scattering cross
section of a very small (Rayleigh) particle can be strongly modified inside a
waveguide. The coupling of the scattered dipolar field with the waveguide modes
induce a resonant enhanced backscattering state of the scatterer-guide system
close to the onset of new modes. The particle effective cross section can then
be as large as the wavelength even far from any transition resonance. As we
will show, a small particle can be strongly accelerated along the guide axis
while being highly confined in a narrow zone of the cross section of the guide.Comment: RevTeX,4 pages,3 PS figure
Optically controlled grippers for manipulating micron-sized particles
We report the development of a joystick controlled gripper for the real-time manipulation of micron-sized objects, driven using holographic optical tweezers (HOTs). The gripper consists of an arrangement of four silica beads, located in optical traps, which can be positioned and scaled in order to trap an object indirectly. The joystick can be used to grasp, move (lateral or axial), and change the orientation of the target object. The ability to trap objects indirectly allows us to demonstrate the manipulation of a strongly scattering micron-sized metallic particle
Theory of Optical Tweezers
We derive a partial-wave (Mie) expansion of the axial force exerted on a
transparent sphere by a laser beam focused through a high numerical aperture
objective. The results hold throughout the range of interest for practical
applications. The ray optics limit is shown to follow from the Mie expansion by
size averaging. Numerical plots show large deviations from ray optics near the
focal region and oscillatory behavior (explained in terms of a simple
interferometer picture) of the force as a function of the size parameter.
Available experimental data favor the present model over previous ones.Comment: 4 pages, 3 figure
Investigation of superconducting interactions and amorphous semiconductors
Research papers on superconducting interactions and properties and on amorphous materials are presented. The search for new superconductors with improved properties was largely concentrated on the study of properties of thin films. An experimental investigation of interaction mechanisms revealed no new superconductivity mechanism. The properties of high transition temperature, type 2 materials prepared in thin film form were studied. A pulsed field solenoid capable of providing fields in excess of 300 k0e was developed. Preliminary X-ray measurements were made of V3Si to determine the behavior of cell constant deformation versus pressure up to 98 kilobars. The electrical properties of amorphous semiconducting materials and bulk and thin film devices, and of amorphous magnetic materials were investigated for developing radiation hard, inexpensive switches and memory elements
Can a charged ring levitate a neutral, polarizable object? Can Earnshaw's Theorem be extended to such objects?
Stable electrostatic levitation and trapping of a neutral, polarizable object
by a charged ring is shown to be theoretically impossible. Earnshaw's Theorem
precludes the existence of such a stable, neutral particle trap.Comment: 11 pages, 1 figur
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