164 research outputs found
Co-word maps of biotechnology: an example of cognitive scientometrics
To analyse developments of scientific fields, scientometrics provides useful tools, provided one is prepared to take the content of scientific articles into account. Such cognitive scientometrics is illustrated by using as data a ten-year period of articles from a biotechnology core journal. After coding with key-words, the relations between articles are brought out by co-word analysis. Maps of the field are given, showing connections between areas and their change over time, and with respect to the institutions in which research is performed. In addition, other approaches are explored, including an indicator of lsquotheoretical levelrsquo of bodies of articles
Metamaterials for light rays: ray optics without wave-optical analog in the ray-optics limit
Volumes of sub-wavelength electromagnetic elements can act like homogeneous
materials: metamaterials. In analogy, sheets of optical elements such as prisms
can act ray-optically like homogeneous sheet materials. In this sense, such
sheets can be considered to be metamaterials for light rays (METATOYs).
METATOYs realize new and unusual transformations of the directions of
transmitted light rays. We study here, in the ray-optics and scalar-wave
limits, the wave-optical analog of such transformations, and we show that such
an analog does not always exist. Perhaps, this is the reason why many of the
ray-optical possibilities offered by METATOYs have never before been
considered.Comment: 10 pages, 3 figures, references update
Local light-ray rotation
We present a sheet structure that rotates the local ray direction through an
arbitrary angle around the sheet normal. The sheet structure consists of two
parallel Dove-prism sheets, each of which flips one component of the local
direction of transmitted light rays. Together, the two sheets rotate
transmitted light rays around the sheet normal. We show that the direction
under which a point light source is seen is given by a Mobius transform. We
illustrate some of the properties with movies calculated by ray-tracing
software.Comment: 9 pages, 6 figure
Graphene-like optical light field and its interaction with two-level atoms
The theoretical basis leading to the creation of a light field with a hexagonal honeycomb structure resembling graphene is considered along with its experimental realization and its interaction with atoms. It is argued that associated with such a light field is an optical dipole potential which leads to the diffraction of the atoms, but the details depend on whether the transverse spread of the atomic wave packet is larger than the transverse dimensions of the optical lattice (resonant Kapitza-Dirac effect) or smaller (optical Stern-Gerlach effect). Another effect in this context involves the creation of gauge fields due to the Berry phase acquired by the atom moving in the light field. The experimental realization of the light field with a honeycomb hexagonal structure is described using holographic methods and we proceed to explore the atom diffraction in the Kapitza-Dirac regime as well as the optical Stern-Gerlach regime, leading to momentum distributions with characteristic but different hexagonal structures. The artificial gauge fields too are shown to have the same hexagonal spatial structure and their magnitude can be significantly large. The effects are discussed with reference to typical parameters for the atoms and the fields
Robust interferometer for the routing of light beams carrying orbital angular momentum
We have developed an interferometer requiring only minimal angular alignment for the routing of beams carrying orbital angular momentum. The MachāZehnder interferometer contains a Dove prism in each arm where each has a mirror plane around which the transverse phase profile is inverted. One consequence of the inversions is that the interferometer needs no alignment. Instead the interferometer defines a unique axis about which the input beam must be coupled. Experimental results are presented for the fringe contrast, reaching a maximum value of 93Ā±1%
Rotational Doppler shift of the phase-conjugated photon
The rotational Doppler shift of a photon with orbital angular momentum is shown to be an even multiple of the angular frequency
of the reference frame rotation when photon is reflected from the
phase-conjugating mirror. We consider the one-arm phase-conjugating
interferometer which contains Dove prisms or other angular momentum
altering elements rotating in opposite directions. When such interferometer is
placed in the rotating vehicle the
rotational Doppler shift appears and rotation of the helical interference
pattern with angular frequency occurs. The
accumulation of angular Doppler shift via successive passage through the
image-inverting prisms is due to the phase conjugation, for conventional
parabolic retroreflector the accumulation is absent. The features of such a
vortex phase conjugating interferometry at the single photon level are
discussed.Comment: 6 pages, 3 figures, submitted to referred journa
Arrays of dark optical traps on a toroidal surface
We have theoretically constructed light fields that can generate optical potentials representing rectangular arrays of dark optical traps on the surface of a torus. The arrays are not diffraction-limited, and their period can in principle be deeply sub-wavelength. We discuss the challenges anticipated in realising such potentials which will be of great interest for quantum simulations
Fourier transforming a trapped Bose-Einstein condensate by waiting a quarter of the trap period: simulation and applications
We investigate the property of isotropic harmonic traps to Fourier transform a weakly interacting BoseāEinstein condensate (BEC) every quarter of a trap period. We solve the GrossāPitaevskii equation numerically to investigate the time evolution of interacting BECs in the context of the Fourier transform, and we suggest potential applications
Simulation of superresolution holography for optical tweezers
Optical tweezers manipulate microscopic particles using foci of light beams. Their performance is therefore limited by diffraction. Using computer simulations of a model system, we investigate the application of superresolution holography for two-dimensional (2D) light shaping in optical tweezers, which can beat the diffraction limit. We use the direct-search and Gerchberg algorithms to shape the center of a light beam into one or two bright spots; we do not constrain the remainder of the beam. We demonstrate that superresolution algorithms can significantly improve the normalized stiffness of an optical trap and the minimum separation at which neighboring traps can be resolved. We also test if such algorithms can be used interactively, as is desirable in optical tweezers
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