176 research outputs found
The low-temperature infrared optical functions of SrTIO3 determined by reflectance spectroscopy and spectroscopic ellipsometry
Transmission of light through periodic arrays of square holes: From a metallic wire mesh to an array of tiny holes
J. Bravo-Abad, L. Martín-Moreno, F. J. García-Vidal, Euan Hendry, and J. Gómez Rivas, Physical Review B, Vol. 76, article 241102(R) (2007). "Copyright © 2007 by the American Physical Society."A complete landscape is presented of the electromagnetic coupling between square holes forming a two-dimensional periodic array in a metallic film. By combining both experimental and theoretical results along with a first-principles Fano model, we study the crossover between the physics of metallic wire meshes (when holes occupy most of the unit cell) and the phenomenon of extraordinary optical transmission, which appears when the size of the holes is very small in comparison with the period of the array
Near-field spectroscopy of silicon dioxide thin films
We analyze the results of scanning near-field infrared spectroscopy performed
on thin films of a-SiO2 on Si substrate. The measured near-field signal
exhibits surface-phonon resonances whose strength has a strong thickness
dependence in the range from 2 to 300 {nm}. These observations are compared
with calculations in which the tip of the near-field infrared spectrometer is
modeled either as a point dipole or an elongated spheroid. The latter model
accounts for the antenna effect of the tip and gives a better agreement with
the experiment. Possible applications of the near-field technique for depth
profiling of layered nanostructures are discussed.Comment: 8 pages, 6 figure
Frequency Comb Assisted Diode Laser Spectroscopy for Measurement of Microcavity Dispersion
While being invented for precision measurement of single atomic transitions,
frequency combs have also become a versatile tool for broadband spectroscopy in
the last years. In this paper we present a novel and simple approach for
broadband spectroscopy, combining the accuracy of an optical fiber-laser-based
frequency comb with the ease-of-use of a tunable external cavity diode laser.
This scheme enables broadband and fast spectroscopy of microresonator modes and
allows for precise measurements of their dispersion, which is an important
precondition for broadband optical frequency comb generation that has recently
been demonstrated in these devices. Moreover, we find excellent agreement of
measured microresonator dispersion with predicted values from finite element
simulations and we show that tailoring microresonator dispersion can be
achieved by adjusting their geometrical properties
Spectral Line-by-Line Pulse Shaping of an On-Chip Microresonator Frequency Comb
We report, for the first time to the best of our knowledge, spectral phase
characterization and line-by-line pulse shaping of an optical frequency comb
generated by nonlinear wave mixing in a microring resonator. Through
programmable pulse shaping the comb is compressed into a train of
near-transform-limited pulses of \approx 300 fs duration (intensity full width
half maximum) at 595 GHz repetition rate. An additional, simple example of
optical arbitrary waveform generation is presented. The ability to characterize
and then stably compress the frequency comb provides new data on the stability
of the spectral phase and suggests that random relative frequency shifts due to
uncorrelated variations of frequency dependent phase are at or below the 100
microHertz level.Comment: 18 pages, 4 figure
Infrared nanoscopy of Dirac plasmons at the graphene-SiO2 interface
We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac
fermions in graphene. This is achieved by confining mid-IR radiation at the
apex of a nanoscale tip: an approach yielding two orders of magnitude increase
in the value of in-plane component of incident wavevector q compared to free
space propagation. At these high wavevectors, the Dirac plasmon is found to
dramatically enhance the near-field interaction with mid-IR surface phonons of
SiO2 substrate. Our data augmented by detailed modeling establish graphene as a
new medium supporting plasmonic effects that can be controlled by gate voltage.Comment: 12 pages, 4 figure
Phase-resolved terahertz self-detection near-field microscopy
At terahertz (THz) frequencies, scattering-type scanning near-field optical microscopy (s-SNOM) based on continuous wave sources mostly relies on cryogenic and bulky detectors, which represents a major constraint for its practical application. Here, we devise a THz s-SNOM system that provides both amplitude and phase contrast and achieves nanoscale (60-70nm) in-plane spatial resolution. It features a quantum cascade laser that simultaneously emits THz frequency light and senses the backscattered optical field through a voltage modulation induced inherently through the self-mixing technique. We demonstrate its performance by probing a phonon-polariton-resonant CsBr crystal and doped black phosphorus flakes
Aggregating sequences that occur in many proteins constitute weak spots of bacterial proteostasis
Aggregation is a sequence-specific process, nucleated by short aggregation-prone regions (APRs) that can be exploited to induce aggregation of proteins containing the same APR. Here, we find that most APRs are unique within a proteome, but that a small minority of APRs occur in many proteins. When aggregation is nucleated in bacteria by such frequently occurring APRs, it leads to massive and lethal inclusion body formation containing a large number of proteins. Buildup of bacterial resistance against these peptides is slow. In addition, the approach is effective against drug-resistant clinical isolates of Escherichiacoli and Acinetobacterbaumannii, reducing bacterial load in a murine bladder infection model. Our results indicate that redundant APRs are weak points of bacterial protein homeostasis and that targeting these may be an attractive antibacterial strategy
Adaptive real-time dual-comb spectroscopy
With the advent of laser frequency combs, coherent light sources that offer
equally-spaced sharp lines over a broad spectral bandwidth have become
available. One decade after revolutionizing optical frequency metrology,
frequency combs hold much promise for significant advances in a growing number
of applications including molecular spectroscopy. Despite its intriguing
potential for the measurement of molecular spectra spanning tens of nanometers
within tens of microseconds at Doppler-limited resolution, the development of
dual-comb spectroscopy is hindered by the extremely demanding high-bandwidth
servo-control conditions of the laser combs. Here we overcome this difficulty.
We experimentally demonstrate a straightforward concept of real-time dual-comb
spectroscopy, which only uses free-running mode-locked lasers without any
phase-lock electronics, a posteriori data-processing, or the need for expertise
in frequency metrology. The resulting simplicity and versatility of our new
technique of adaptive dual-comb spectroscopy offer a powerful transdisciplinary
instrument that may spark off new discoveries in molecular sciences.Comment: 10 pages, 5 figure
Hearing loss in Pompe disease revisited: results from a study of 24 children
Little information is available regarding the auditory function in Pompe patients. Hearing loss has been reported in classic infantile patients, but it is still unknown whether central nervous system involvement interferes with auditory function and whether enzyme replacement therapy can improve hearing. Audi
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