122 research outputs found
Normal and lateral Casimir force: Advances and prospects
We discuss recent experimental and theoretical results on the Casimir force
between real material bodies made of different materials. Special attention is
paid to calculations of the normal Casimir force acting perpendicular to the
surface with the help of the Lifshitz theory taking into account the role of
free charge carriers. Theoretical results for the thermal Casimir force acting
between metallic, dielectric and semiconductor materials are presented and
compared with available experimental data. Main attention is concentrated on
the possibility to control the magnitude and sign of the Casimir force for
applications in nanotechnology. In this respect we consider experiments on the
optical modulation of the Casimir force between metal and semiconductor test
bodies with laser light. Another option is the use of ferromagnetic materials,
specifically, ferromagnetic dielectrics. Under some conditions this allows to
get Casimir repulsion. The lateral Casimir force acting between sinusoidally
corrugated surfaces can be considered as some kind of noncontact friction
caused by zero-point oscillations of the electromagnetic field. Recent
experiments and computations using the exact theory have demonstrated the role
of diffraction-type effects in this phenomenon and the possibility to get
asymmetric force profiles. Conclusion is made that the Casimir force may play
important role in the operation of different devices on the nanoscale.Comment: 27 pages, 13 figures; Invited keynote lecture at the 2nd
International Conference on Science of Friction, Ise-Shima, Mie, Japan,
September 13-18, 2010; to appear in J. Phys.: Conf. Se
On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration
We report on measurements of forces acting between two conducting surfaces in
a spherical-plane configuration in the 35 nm-1 micrometer separation range. The
measurements are obtained by performing electrostatic calibrations followed by
a residual analysis after subtracting the electrostatic-dependent component. We
find in all runs optimal fitting of the calibrations for exponents smaller than
the one predicted by electrostatics for an ideal sphere-plane geometry. We also
find that the external bias potential necessary to minimize the electrostatic
contribution depends on the sphere-plane distance. In spite of these anomalies,
by implementing a parametrixation-dependent subtraction of the electrostatic
contribution we have found evidence for short-distance attractive forces of
magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss
the relevance of our findings in the more general context of Casimir-Lifshitz
force measurements, with particular regard to the critical issues of the
electrical and geometrical characterization of the involved surfaces.Comment: 22 pages, 15 figure
Electromagnetic field correlations near a surface with a nonlocal optical response
The coherence length of the thermal electromagnetic field near a planar
surface has a minimum value related to the nonlocal dielectric response of the
material. We perform two model calculations of the electric energy density and
the field's degree of spatial coherence. Above a polar crystal, the lattice
constant gives the minimum coherence length. It also gives the upper limit to
the near field energy density, cutting off its divergence. Near an
electron plasma described by the semiclassical Lindhard dielectric function,
the corresponding length scale is fixed by plasma screening to the Thomas-Fermi
length. The electron mean free path, however, sets a larger scale where
significant deviations from the local description are visible.Comment: 15 pages, 7 figure files (.eps), \documentclass[global]{svjour},
accepted in special issue "Optics on the Nanoscale" (Applied Physics B, eds.
V. Shalaev and F. Tr\"ager
Photon Management in Two-Dimensional Disordered Media
Elaborating reliable and versatile strategies for efficient light coupling
between free space and thin films is of crucial importance for new technologies
in energy efficiency. Nanostructured materials have opened unprecedented
opportunities for light management, notably in thin-film solar cells. Efficient
coherent light trapping has been accomplished through the careful design of
plasmonic nanoparticles and gratings, resonant dielectric particles and
photonic crystals. Alternative approaches have used randomly-textured surfaces
as strong light diffusers to benefit from their broadband and wide-angle
properties. Here, we propose a new strategy for photon management in thin films
that combines both advantages of an efficient trapping due to coherent optical
effects and broadband/wide-angle properties due to disorder. Our approach
consists in the excitation of electromagnetic modes formed by multiple light
scattering and wave interference in two-dimensional random media. We show, by
numerical calculations, that the spectral and angular responses of thin films
containing disordered photonic patterns are intimately related to the in-plane
light transport process and can be tuned through structural correlations. Our
findings, which are applicable to all waves, are particularly suited for
improving the absorption efficiency of thin-film solar cells and can provide a
novel approach for high-extraction efficiency light-emitting diodes
Thermal correction to the Casimir force, radiative heat transfer, and an experiment
The low-temperature asymptotic expressions for the Casimir interaction
between two real metals described by Leontovich surface impedance are obtained
in the framework of thermal quantum field theory. It is shown that the Casimir
entropy computed using the impedance of infrared optics vanishes in the limit
of zero temperature. By contrast, the Casimir entropy computed using the
impedance of the Drude model attains at zero temperature a positive value which
depends on the parameters of a system, i.e., the Nernst heat theorem is
violated. Thus, the impedance of infrared optics withstands the thermodynamic
test, whereas the impedance of the Drude model does not. We also perform a
phenomenological analysis of the thermal Casimir force and of the radiative
heat transfer through a vacuum gap between real metal plates. The
characterization of a metal by means of the Leontovich impedance of the Drude
model is shown to be inconsistent with experiment at separations of a few
hundred nanometers. A modification of the impedance of infrared optics is
suggested taking into account relaxation processes. The power of radiative heat
transfer predicted from this impedance is several times less than previous
predictions due to different contributions from the transverse electric
evanescent waves. The physical meaning of low frequencies in the Lifshitz
formula is discussed. It is concluded that new measurements of radiative heat
transfer are required to find out the adequate description of a metal in the
theory of electromagnetic fluctuations.Comment: 19 pages, 4 figures. svjour.cls is used, to appear in Eur. Phys. J.
Resonant Thermoelectric Nanophotonics
Photodetectors are typically based either on photocurrent generation from electronâhole pairs in semiconductor structures or on bolometry for wavelengths that are below bandgap absorption. In both cases, resonant plasmonic and nanophotonic structures have been successfully used to enhance performance. Here, we show subwavelength thermoelectric nanostructures designed for resonant spectrally selective absorption, which creates large localized temperature gradients even with unfocused, spatially uniform illumination to generate a thermoelectric voltage. We show that such structures are tunable and are capable of wavelength-specific detection, with an input power responsivity of up to 38 VâW^(â1), referenced to incident illumination, and bandwidth of nearly 3 kHz. This is obtained by combining resonant absorption and thermoelectric junctions within a single suspended membrane nanostructure, yielding a bandgap-independent photodetection mechanism. We report results for both bismuth telluride/antimony telluride and chromel/alumel structures as examples of a potentially broader class of resonant nanophotonic thermoelectric materials for optoelectronic applications such as non-bandgap-limited hyperspectral and broadband photodetectors
Near-field Electrical Detection of Optical Plasmons and Single Plasmon Sources
Photonic circuits can be much faster than their electronic counterparts, but
they are difficult to miniaturize below the optical wavelength scale. Nanoscale
photonic circuits based on surface plasmon polaritons (SPs) are a promising
solution to this problem because they can localize light below the diffraction
limit. However, there is a general tradeoff between the localization of an SP
and the efficiency with which it can be detected with conventional far-field
optics. Here we describe a new all-electrical SP detection technique based on
the near-field coupling between guided plasmons and a nanowire field-effect
transistor. We use the technique to electrically detect the plasmon emission
from an individual colloidal quantum dot coupled to an SP waveguide. Our
detectors are both nanoscale and highly efficient (0.1 electrons/plasmon), and
a plasmonic gating effect can be used to amplify the signal even higher (up to
50 electrons/plasmon). These results enable new on-chip optical sensing
applications and are a key step towards "dark" optoplasmonic nanocircuits in
which SPs can be generated, manipulated, and detected without involving
far-field radiation.Comment: manuscript followed by supplementary informatio
Metal nanoparticles for microscopy and spectroscopy
Metal nanoparticles interact strongly with light due to a resonant response of their free electrons. These âplasmonâ resonances appear as very strong extinction and scattering for particular wavelengths, and result in high enhancements of the local field compared to the incident electric field. In this chapter we introduce the reader to the optical properties of single plasmon particles as well as finite clusters and periodic lattices, and discuss several applications
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