963 research outputs found
Epsilon-Near-Zero Al-Doped ZnO for Ultrafast Switching at Telecom Wavelengths: Outpacing the Traditional Amplitude-Bandwidth Trade-Off
Transparent conducting oxides have recently gained great attention as
CMOS-compatible materials for applications in nanophotonics due to their low
optical loss, metal-like behavior, versatile/tailorable optical properties, and
established fabrication procedures. In particular, aluminum doped zinc oxide
(AZO) is very attractive because its dielectric permittivity can be engineered
over a broad range in the near infrared and infrared. However, despite all
these beneficial features, the slow (> 100 ps) electron-hole recombination time
typical of these compounds still represents a fundamental limitation impeding
ultrafast optical modulation. Here we report the first epsilon-near-zero AZO
thin films which simultaneously exhibit ultra-fast carrier dynamics (excitation
and recombination time below 1 ps) and an outstanding reflectance modulation up
to 40% for very low pump fluence levels (< 4 mJ/cm2) at the telecom wavelength
of 1.3 {\mu}m. The unique properties of the demonstrated AZO thin films are the
result of a low temperature fabrication procedure promoting oxygen vacancies
and an ultra-high carrier concentration. As a proof-of-concept, an all-optical
AZO-based plasmonic modulator achieving 3 dB modulation in 7.5 {\mu}m and
operating at THz frequencies is numerically demonstrated. Our results overcome
the traditional "modulation depth vs. speed" trade-off by at least an order of
magnitude, placing AZO among the most promising compounds for
tunable/switchable nanophotonics.Comment: 14 pages, 9 figures, 1 tabl
Ultra-compact modulators based on novel CMOS-compatible plasmonic materials
We propose several planar layouts of ultra-compact plasmonic waveguide
modulators that utilize alternative CMOS-compatible materials. The modulation
is efficiently achieved by tuning the carrier concentration in a transparent
conducting oxide layer, thereby tuning the waveguide either in plasmonic
resonance or off-resonance. Resonance significantly increases the absorption
coefficient of the plasmonic waveguide, which enables larger modulation depth.
We show that an extinction ratio of 86 dB/um can be achieved, allowing for a
3-dB modulation depth in less than one micron at the telecommunication
wavelength. Our multilayer structures can potentially be integrated with
existing plasmonic and photonic waveguides as well as novel semiconductor-based
hybrid photonic/electronic circuits
Navigational infrastructure at the East Pacific Rise 9°50′N area following the 2005–2006 eruption : seafloor benchmarks and near-bottom multibeam surveys
Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008):Q11T04, doi:10.1029/2008GC002070.Four seafloor benchmarks were deployed with ROV Jason2 at frequently visited areas along the northern East Pacific Rise (NEPR) ridge crest near 9°50′N, within the Ridge2000 EPR integrated study site (ISS) bull's eye. When used in concert with established deep-ocean acoustic positioning techniques, these benchmarks provide navigational infrastructure to facilitate the integration of near-bottom data at this site by allowing efficient and quantitative coregistration of data and observations collected on multiple dives and over multiple cruises. High-resolution, near-bottom multibeam bathymetric surveys also were conducted along and across the ridge crest to provide a morphological and geological context for the benchmark areas. We describe the navigation and data processing techniques used to constrain the benchmark positions and outline operational details to effectively use benchmarks at this and other deep-ocean sites where multidisciplinary time series studies are conducted. The well-constrained positions of the benchmarks provide a consistent geospatial framework that can be used to limit navigational uncertainties during seafloor sampling and mapping programs and enable accurate spatial coregistration and integration of observations. These data are important to test a range of multidisciplinary hypotheses that seek to link geological, chemical, and biological processes associated with crustal accretion and energy transfer from the mantle to the hydrosphere at mid-ocean ridges
Cross-sections for nuclide production in 56Fe target irradiated by 300, 500,750, 1000, 1500, and 2600 MeV protons compared with data on hydrogen target irradiation by 300, 500, 750, 1000, and 1500 MeV/nucleon 56Fe ions
Cross-sections for radioactive nuclide production in 56Fe(p,x) reactions at
300, 500, 750, 1000, 1500, and 2600 MeV were measured using the ITEP U-10
proton accelerator. In total, 221 independent and cumulative yields of products
of half-lives from 6.6 min to 312 days have been obtained via the
direct-spectrometry method. The measured data have been compared with the
experimental data obtained elsewhere by the direct and inverse kinematics
methods and with calculations by 15 codes, namely: MCNPX (INCL, CEM2k, BERTINI,
ISABEL), LAHET (BERTINI, ISABEL), CEM03 (.01, .G1, .S1), LAQGSM03 (.01, .G1,
>.S1), CASCADE-2004, LAHETO, and BRIEFF. Most of our data are in a good
agreement with the inverse kinematics results and disprove the results of some
earlier activation measurements that were quite different from the inverse
kinematics measurements. The most significant calculation-to-experiment
differences are observed in the yields of the A<30 light nuclei, indicating
that further improvements in nuclear reaction models are needed, and pointing
out as well to a necessity of more complete measurements of such reactions.Comment: 53 pages, 9 figures, 6 tables, only pdf file, submitted to Phys. Rev.
Controlling hybrid nonlinearities in transparent conducting oxides via two-colour excitation
Nanophotonics and metamaterials have revolutionised the way we think about
optical space (epsilon, mu), enabling us to engineer the refractive index
almost at will, to confine light to the smallest of the volumes, and to
manipulate optical signals with extremely small footprints and energy
requirements. Significant efforts are now devoted to finding suitable materials
and strategies for the dynamic control of the optical properties. Transparent
conductive oxides exhibit large ultrafast nonlinearities under both interband
and intraband excitations. Here, we show that combining these two effects in
aluminium-doped zinc oxide via a two colour laser field discloses new material
functionalities. Owing to the independence of the two nonlinearities the
ultrafast temporal dynamics of the material permittivity can be designed by
acting on the amplitude and delay of the two fields. We demonstrate the
potential applications of this novel degree of freedom by dynamically
addressing the modulation bandwidth and optical spectral tuning of a probe
optical pulse
Enhanced nonlinear refractive index in ε-near-zero materials
New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here, we demonstrate a universal approach based on the low linear permittivity values attained in the ε-near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a sixfold increase of the Kerr nonlinear refractive index (n2) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics.Publisher PDFPeer reviewe
Mid-water current aided localization for autonomous underwater vehicles
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Autonomous Robots 40 (2016): 1207–1227, doi:10.1007/s10514-016-9547-3.Survey-class Autonomous Underwater Vehi-
cles (AUVs) typically rely on Doppler Velocity Logs
(DVL) for precision localization near the seafloor. In
cases where the seafloor depth is greater than the DVL
bottom-lock range, localizing between the surface and
the seafloor presents a localization problem since both
GPS and DVL observations are unavailable in the mid-
water column. This work proposes a solution to this
problem that exploits the fact that current profile layers
of the water column are near constant over short time
scales (in the scale of minutes). Using observations of
these currents obtained with the Acoustic Doppler Cur-
rent Profiler (ADCP) mode of the DVL during descent,
along with data from other sensors, the method dis-
cussed herein constrains position error. The method is
validated using field data from the Sirius AUV coupled
with view-based Simultaneous Localization and Map-
ping (SLAM) and on descents up to 3km deep with the
Sentry AUV.This work is supported in part by NCRIS IMOS, the
Australian Research Council (ARC), the New South
Wales Government and the Woods Hole Oceanographic
Institution.2017-02-1
Modal Logics of Topological Relations
Logical formalisms for reasoning about relations between spatial regions play
a fundamental role in geographical information systems, spatial and constraint
databases, and spatial reasoning in AI. In analogy with Halpern and Shoham's
modal logic of time intervals based on the Allen relations, we introduce a
family of modal logics equipped with eight modal operators that are interpreted
by the Egenhofer-Franzosa (or RCC8) relations between regions in topological
spaces such as the real plane. We investigate the expressive power and
computational complexity of logics obtained in this way. It turns out that our
modal logics have the same expressive power as the two-variable fragment of
first-order logic, but are exponentially less succinct. The complexity ranges
from (undecidable and) recursively enumerable to highly undecidable, where the
recursively enumerable logics are obtained by considering substructures of
structures induced by topological spaces. As our undecidability results also
capture logics based on the real line, they improve upon undecidability results
for interval temporal logics by Halpern and Shoham. We also analyze modal
logics based on the five RCC5 relations, with similar results regarding the
expressive power, but weaker results regarding the complexity
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