532 research outputs found
Strong absorption and selective thermal emission from a mid-infrared metamaterial
We demonstrate thin-film metamaterials with resonances in the mid-infrared
wavelength range. Our structures are numerically modeled and experimentally
characterized by reflection and angularly-resolved thermal emission
spectroscopy. We demonstrate strong and controllable absorption resonances
across the mid-infrared wavelength range. In addition, the polarized thermal
emission from these samples is shown to be highly selective and largely
independent of emission angles from normal to 45 degrees. Experimental results
are compared to numerical models with excellent agreement. Such structures hold
promise for large-area, low-cost metamaterial coatings for control of gray- or
black-body thermal signatures, as well as for possible mid-IR sensing
applications.Comment: The following article has been submitted to Appl. Phys. Lett. After
it is published, it will be found at http://apl.aip.org/. 14 pages including
4 figure page
Phonitons as a sound-based analogue of cavity quantum electrodynamics
A quantum mechanical superposition of a long-lived, localized phonon and a
matter excitation is described. We identify a realization in strained silicon:
a low-lying donor transition (P or Li) driven solely by acoustic phonons at
wavelengths where high-Q phonon cavities can be built. This phonon-matter
resonance is shown to enter the strongly coupled regime where the "vacuum" Rabi
frequency exceeds the spontaneous phonon emission into non-cavity modes, phonon
leakage from the cavity, and phonon anharmonicity and scattering. We introduce
a micropillar distributed Bragg reflector Si/Ge cavity, where Q=10^5-10^6 and
mode volumes V<=25*lambda^3 are reachable. These results indicate that single
or many-body devices based on these systems are experimentally realizable.Comment: Published PRL version. Note that the previous arXiv version has more
commentary, figures, etc. Also see http://research.tahan.com
Phonons in Random Elastic Media and the Boson Peak
We show that the density of states of random wave equations, normalized by
the square of the frequency, has a peak - sometimes narrow and sometimes broad
- in the range of wave vectors between the disorder correlation length and the
interatomic spacing. The results of this letter may be relevant for
understanding vibrational spectra and light propagation in disordered solids
Once More About the Possibility of Determining the Local Electron Concentration by the Dispersion Method with the Help of AES and on New Ionization Maxima in the Ionosphere
Reliability of ionospheric density measurements by satellites using dispersion metho
Application of High-Power Electrical Sparks for Dynamic Compaction of Soil
The paper describes an electrical discharge technology, applied for soil compaction around a borehole, filled with hardening grout, in operations for erection of micropiles, cast piles, soil anchors and soil nails. The technology consists in that 150-250 microsecond long electrical sparks are generated with 6-second period in borehole. The sparks have 30-40 kJ energy, which is roughly of the same order of magnitude as a pile drop hammer. But a single electrical spark has 200-250 MW because of its short duration. Such pulses compact the contact layer of soil and thus increase bearing capacity of piles, anchors or soil nails times 1.5-2.0. Electrical spark in soil is a practically non-observable event, prohibiting any instrumentation near it, which so far can only allow its qualitative investigation in water rather than in soil. The experiments in water were staged in lab on a set-up, generating 5 kJ sparks, with electronic registration of time-dependent registration of pulse behavior. It was found that longer pulse efficiency is higher and can be increased by addition of special admixtures. Full-size bored piles, micropiles and soil anchors were tested in-situ on construction sites, having various soil conditions. The test data yielded that pile (anchor, nail) bearing capacity could be increased times 1.5-2.0 by high-energy electrical spark treatment, as compared to conventional technology (without electrical spark treatment)
A non-destructive analytic tool for nanostructured materials : Raman and photoluminescence spectroscopy
Modern materials science requires efficient processing and characterization
techniques for low dimensional systems. Raman spectroscopy is an important
non-destructive tool, which provides enormous information on these materials.
This understanding is not only interesting in its own right from a physicist's
point of view, but can also be of considerable importance in optoelectronics
and device applications of these materials in nanotechnology. The commercial
Raman spectrometers are quite expensive. In this article, we have presented a
relatively less expensive set-up with home-built collection optics attachment.
The details of the instrumentation have been described. Studies on four classes
of nanostructures - Ge nanoparticles, porous silicon (nanowire), carbon
nanotubes and 2D InGaAs quantum layers, demonstrate that this unit can be of
use in teaching and research on nanomaterials.Comment: 32 pages, 13 figure
A scattering approach to Casimir forces and radiative heat transfer for nanostructured surfaces out of thermal equilibrium
We develop an exact method for computing Casimir forces and the power of
radiative heat transfer between two arbitrary nanostructured surfaces out of
thermal equilibrium. The method is based on a generalization of the scattering
approach recently used in investigations on the Casimir effect. Analogously to
the equilibrium case, we find that also out of thermal equilibrium the shape
and composition of the surfaces enter only through their scattering matrices.
The expressions derived provide exact results in terms of the scattering
matrices of the intervening surfaces.Comment: 7 pages, accepted for publication in Physical Review
Thermalization via Heat Radiation of an Individual Object Thinner than the Thermal Wavelength
Modeling and investigating the thermalization of microscopic objects with
arbitrary shape from first principles is of fundamental interest and may lead
to technical applications. Here, we study, over a large temperature range, the
thermalization dynamics due to far-field heat radiation of an individual,
deterministically produced silica fiber with a predetermined shape and a
diameter smaller than the thermal wavelength. The temperature change of the
subwavelength-diameter fiber is determined through a measurement of its optical
path length in conjunction with an ab initio thermodynamic model of the fiber
structure. Our results show excellent agreement with a theoretical model that
considers heat radiation as a volumetric effect and takes the emitter shape and
size relative to the emission wavelength into account
Generation and remote detection of THz sound using semiconductor superlattices
The authors introduce a novel approach to study the propagation of high
frequency acoustic phonons in which the generation and detection involves two
spatially separated superlattices apart. Propagating modes
of frequencies up to escape from the superlattice where they
are generated and reach the second superlattice where they are detected. The
measured frequency spectrum reveals finite size effects, which can be accounted
for by a continuum elastic model.Comment: Submitted to Applied Physics Letter
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