624 research outputs found
Engineered Optical Nonlocality in Nanostructured Metamaterials
We analyze dispersion properties of metal-dielectric nanostructured
metamaterials. We demonstrate that, in a sharp contrast to the results for the
corresponding effective medium, the structure demonstrates strong optical
nonlocality due to excitation of surface plasmon polaritons that can be
engineered by changing a ratio between the thicknesses of metal and dielectric
layers. In particular, this nonlocality allows the existence of an additional
extraordinary wave that manifests itself in the splitting of the TM-polarized
beam scattered at an air-metamaterial interface
Anomalous transparency of water-air interface for low-frequency sound
Sound transmission through water-air interface is normally weak because of a
strong mass density contrast. Here we show that the transparency of the
interface increases dramatically at low frequencies. Rather counterintuitively,
almost all acoustic energy emitted by a sufficiently shallow monopole source
under water is predicted to be radiated into atmosphere. Physically, increased
transparency at lower frequencies is due to the increasing role of
inhomogeneous waves and a destructive interference of direct and
surface-reflected waves under water. The phenomenon of anomalous transparency
has significant implications for acoustic communication across the water-air
interface, generation of ambient noise, and detection of underwater explosions.Comment: 29 pages, including 4 figure
Disorder-induced cavities, resonances, and lasing in randomly-layered media
We study, theoretically and experimentally, disorder-induced resonances in
randomly-layered samples,and develop an algorithm for the detection and
characterization of the effective cavities that give rise to these resonances.
This algorithm enables us to find the eigen-frequencies and pinpoint the
locations of the resonant cavities that appear in individual realizations of
random samples, for arbitrary distributions of the widths and refractive
indices of the layers. Each cavity is formed in a region whose size is a few
localization lengths. Its eigen-frequency is independent of the location inside
the sample, and does not change if the total length of the sample is increased
by, for example, adding more scatterers on the sides. We show that the total
number of cavities, , and resonances, , per
unit frequency interval is uniquely determined by the size of the disordered
system and is independent of the strength of the disorder. In an active,
amplifying medium, part of the cavities may host lasing modes whose number is
less than . The ensemble of lasing cavities behaves as
distributed feedback lasers, provided that the gain of the medium exceeds the
lasing threshold, which is specific for each cavity. We present the results of
experiments carried out with single-mode optical fibers with gain and
randomly-located resonant Bragg reflectors (periodic gratings). When the fiber
was illuminated by a pumping laser with an intensity high enough to overcome
the lasing threshold, the resonances revealed themselves by peaks in the
emission spectrum. Our experimental results are in a good agreement with the
theory presented here.Comment: minor correction
Ray-based description of normal mode amplitudes in a range-dependent waveguide
An analogue of the geometrical optics for description of the modal structure
of a wave field in a range-dependent waveguide is considered. In the scope of
this approach the mode amplitude is expressed through solutions of the ray
equations. This analytical description accounts for mode coupling and remains
valid in a nonadiabatic environment. It has been used to investigate the
applicability condition of the adiabatic approximation. An applicability
criterion is formulated as a restriction on variations of the action variable
of the ray.Comment: 11 pages, 5 figure
Surface plasmon resonance study of the actin-myosin sarcomeric complex and tubulin dimers
Biosensors based on the principle of surface plasmon resonance (SPR)
detection were used to measure biomolecular interactions in sarcomeres and
changes of the dielectric constant of tubulin samples with varying
concentration. At SPR, photons of laser light efficiently excite surface
plasmons propagating along a metal (gold) film. This resonance manifests itself
as a sharp minimum in the reflection of the incident laser light and occurs at
a characteristic angle. The dependence of the SPR angle on the dielectric
permittivity of the sample medium adjacent to the gold film allows the
monitoring of molecular interactions at the surface. We present results of
measurements of cross-bridge attachment/detachment within intact mouse heart
muscle sarcomeres and measurements on bovine tubulin molecules pertinent to
cytoskeletal signal transduction models.Comment: Submitted to Journal of Modern Optics *Corresponding author: Andreas
Mershin ([email protected]
Acoustic scattering from double-diffusive microstructure
Author Posting. © Acoustical Society of America, 2007. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 122 (2007): 1449-1462, doi:10.1121/1.2764475.Laboratory measurements of high-frequency broadband acoustic backscattering (200–600 kHz) from the diffusive regime of double-diffusive microstructure have been performed. This type of microstructure, which was characterized using direct microstructure and optical shadowgraph techniques, is identified by sharp density and sound speed interfaces separating well-mixed layers. Vertical acoustic backscattering measurements were performed for a range of physical parameters controlling the double-diffusive microstructure. The echoes have been analyzed in both the frequency domain, providing information on the spectral response of the scattering, and in the time domain, using pulse compression techniques. High levels of variability were observed, associated with interface oscillations and turbulent plumes, with many echoes showing significant spectral structure. Acoustic estimates of interface thickness (1–3 cm), obtained for the echoes with exactly two peaks in the compressed pulse output, were in good agreement with estimates based on direct microstructure and optical shadowgraph measurements. Predictions based on a one-dimensional weak-scattering model that includes the actual density and sound speed profiles agree reasonably with the measured scattering. A remote-sensing tool for mapping oceanic microstructure, such as high-frequency broadband acoustic scattering, could lead to a better understanding of the extent and evolution of double-diffusive layering, and to the importance of double diffusion to oceanic mixing.Funding for this project was provided
by the Ocean Acoustics program at the Office of Naval
Research and by the Woods Hole Oceanographic Institution
Cecil and Ida Greene Technology Award. Tetjana Ross was
supported by the WHOI Postdoctoral Scholarship through
the generous support of the Doherty Foundation
Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media
Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal
the exis-tence of an unusually long-lived acoustic mode at ~ 0.6 THz, which
couples weakly to the environment by evading the sample boundaries. Classical
as well as quantum states that steer clear of surfaces are generally shown to
occur in the spectrum of periodic struc-tures, for most boundary conditions.
These surface-avoiding waves are associated with frequencies outside forbidden
gaps and wavevectors in the vicinity of the center and edge of the Brillouin
zone. Possible consequences for surface science and resonant cavity
ap-plications are discussed.Comment: 16 pages, 3 figure
Influence of positional correlations on the propagation of waves in a complex medium with polydisperse resonant scatterers
We present experimental results on a model system for studying wave
propagation in a complex medium exhibiting low frequency resonances. These
experiments enable us to investigate a fundamental question that is relevant
for many materials, such as metamaterials, where low-frequency scattering
resonances strongly influence the effective medium properties. This question
concerns the effect of correlations in the positions of the scatterers on the
coupling between their resonances, and hence on wave transport through the
medium. To examine this question experimentally, we measure the effective
medium wave number of acoustic waves in a sample made of bubbles embedded in an
elastic matrix over a frequency range that includes the resonance frequency of
the bubbles. The effective medium is highly dispersive, showing peaks in the
attenuation and the phase velocity as functions of the frequency, which cannot
be accurately described using the Independent Scattering Approximation (ISA).
This discrepancy may be explained by the effects of the positional correlations
of the scatterers, which we show to be dependent on the size of the scatterers.
We propose a self-consistent approach for taking this "polydisperse
correlation" into account and show that our model better describes the
experimental results than the ISA
Head Wave Correlations in Ambient Noise
Ambient ocean noise is processed with a vertical line array to reveal coherent time-separated arrivals suggesting the presence of head wave multipath propagation. Head waves, which are critically propagating water waves created by seabed waves traveling parallel to the water-sediment interface, can propagate faster than water-only waves. Such eigenrays are much weaker than water-only eigenrays, and are often completely overshadowed by them. Surface-generated noise is different whereby it amplifies the coherence between head waves and critically propagating water-only waves, which is measured by cross-correlating critically steered beams. This phenomenon is demonstrated both experimentally and with a full wave simulation
Enhanced transmission band in periodic media with loss modulation
Copyright (2014) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
The following article appeared in: Applied Physics Letters 105, 204104 (2014); doi: 10.1063/1.4902387 and may be found at: http://dx.doi.org/10.1063/1.490238.We study the propagation of waves in a periodic array of absorbing layers. We report an anomalous increase of wave transmission through the structure related to a decrease of the absorption around the Bragg frequencies. The effect is first discussed in terms of a generic coupled wave model extended to include losses, and its predictions can be applied to different types of waves propagating in media with periodic modulation of the losses at the wavelength scale. The particular case of sound waves in an array of porous layers embedded in air is considered. An experiment designed to test the predictions demonstrates the existence of the enhanced transmission band. (C) 2014 AIP Publishing LLC.The work was supported by Spanish Ministry of Science and Innovation and European Union FEDER through Projects FIS2011-29731-C02-01 and -02, also MAT2009-09438. A.M.Y. would like to thank the Erasmus Mundus Project (WELCOME program) for supporting him. V.R.G. acknowledges financial support from the "Pays-de-la-Loire" through the post-doctoral program.Cebrecos Ruiz, A.; Picó Vila, R.; Romero García, V.; Yasser, AM.; Maigyte, L.; Herrero, R.; Botey, M.... (2014). Enhanced transmission band in periodic media with loss modulation. Applied Physics Letters. 105(20):204104-1-204104-4. doi:10.1063/1.4902387S204104-1204104-410520Figotin, A., & Vitebskiy, I. (2008). Absorption suppression in photonic crystals. Physical Review B, 77(10). doi:10.1103/physrevb.77.104421Figotin, A., & Vitebskiy, I. (2010). Magnetic Faraday rotation in lossy photonic structures. Waves in Random and Complex Media, 20(2), 298-318. doi:10.1080/17455030.2010.482575Erokhin, S. G., Lisyansky, A. A., Merzlikin, A. M., Vinogradov, A. P., & Granovsky, A. B. (2008). Photonic crystals built on contrast in attenuation. Physical Review B, 77(23). doi:10.1103/physrevb.77.233102Kumar, N., Botey, M., Herrero, R., Loiko, Y., & Staliunas, K. (2012). High-directional wave propagation in periodic loss modulated materials. Photonics and Nanostructures - Fundamentals and Applications, 10(4), 644-650. doi:10.1016/j.photonics.2012.06.003Staliunas, K., Herrero, R., & Vilaseca, R. (2009). Subdiffraction and spatial filtering due to periodic spatial modulation of the gain-loss profile. Physical Review A, 80(1). doi:10.1103/physreva.80.013821Kumar, N., Herrero, R., Botey, M., & Staliunas, K. (2013). Flat lensing by periodic loss-modulated materials. Journal of the Optical Society of America B, 30(10), 2684. doi:10.1364/josab.30.002684Psarobas, I. E. (2001). Viscoelastic response of sonic band-gap materials. Physical Review B, 64(1). doi:10.1103/physrevb.64.012303Lee, C.-Y., Leamy, M. J., & Nadler, J. H. (2010). Frequency band structure and absorption predictions for multi-periodic acoustic composites. Journal of Sound and Vibration, 329(10), 1809-1822. doi:10.1016/j.jsv.2009.11.030Laude, V., Escalante, J. M., & Martínez, A. (2013). Effect of loss on the dispersion relation of photonic and phononic crystals. Physical Review B, 88(22). doi:10.1103/physrevb.88.224302Hwan Oh, J., Jae Kim, Y., & Young Kim, Y. (2013). Wave attenuation and dissipation mechanisms in viscoelastic phononic crystals. Journal of Applied Physics, 113(10), 106101. doi:10.1063/1.4795285Hussein, M. I. (2009). Theory of damped Bloch waves in elastic media. Physical Review B, 80(21). doi:10.1103/physrevb.80.212301Andreassen, E., & Jensen, J. S. (2013). Analysis of Phononic Bandgap Structures With Dissipation. Journal of Vibration and Acoustics, 135(4). doi:10.1115/1.4023901Allard, J. F., & Atalla, N. (2009). Propagation of Sound in Porous Media. doi:10.1002/9780470747339Tournat, V., Pagneux, V., Lafarge, D., & Jaouen, L. (2004). Multiple scattering of acoustic waves and porous absorbing media. Physical Review E, 70(2). doi:10.1103/physreve.70.026609Umnova, O., Attenborough, K., & Linton, C. M. (2006). Effects of porous covering on sound attenuation by periodic arrays of cylinders. The Journal of the Acoustical Society of America, 119(1), 278-284. doi:10.1121/1.2133715Romero-García, V., Sánchez-Pérez, J. V., & Garcia-Raffi, L. M. (2010). Evanescent modes in sonic crystals: Complex dispersion relation and supercell approximation. Journal of Applied Physics, 108(4), 044907. doi:10.1063/1.3466988Christensen, J., Romero-García, V., Picó, R., Cebrecos, A., de Abajo, F. J. G., Mortensen, N. A., … Sánchez-Morcillo, V. J. (2014). Extraordinary absorption of sound in porous lamella-crystals. Scientific Reports, 4(1). doi:10.1038/srep04674Kogelnik, H., & Shank, C. V. (1972). Coupled‐Wave Theory of Distributed Feedback Lasers. Journal of Applied Physics, 43(5), 2327-2335. doi:10.1063/1.166149
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