Perfect absorption in GaAs metasurfaces near the bandgap edge.

Perfect optical absorption occurs in a metasurface that supports two degenerate and critically-coupled modes of opposite symmetry. The challenge in designing a perfectly absorbing metasurface for a desired wavelength and material stems from the fact that satisfying these conditions requires multi-dimensional optimization often with parameters affecting optical resonances in non-trivial ways. This problem comes to the fore in semiconductor metasurfaces operating near the bandgap wavelength, where intrinsic material absorption varies significantly. Here we devise and demonstrate a systematic process by which one can achieve perfect absorption in GaAs metasurfaces for a desired wavelength at different levels of intrinsic material absorption, eliminating the need for trial and error in the design process. Using this method, we show that perfect absorption can be achieved not only at wavelengths where GaAs exhibits high absorption, but also at wavelengths near the bandgap edge. In this region, absorption is enhanced by over one order of magnitude compared a layer of unstructured GaAs of the same thickness.

Near-field spectroscopy and tuning of sub-surface modes in plasmonic terahertz resonators.

Highly confined modes in THz plasmonic resonators comprising two metallic elements can enhance light-matter interaction for efficient THz optoelectronic devices. We demonstrate that sub-surface modes in such double-metal resonators can be revealed with an aperture-type near-field probe and THz time-domain spectroscopy despite strong mode confinement in the dielectric spacer. The sub-surface modes couple a fraction of their energy to the resonator surface via surface waves, which we detected with the near-field probe. We investigated two resonator geometries: a λ/2 double-metal patch antenna with a 2 µm thick dielectric spacer, and a three-dimensional meta-atom resonator. THz time-domain spectroscopy analysis of the fields at the resonator surface displays spectral signatures of sub-surface modes. Investigations of strong light-matter coupling in resonators with sub-surface modes therefore can be assisted by the aperture-type THz near-field probes. Furthermore, near-field interaction of the probe with the resonator enables tuning of the resonance frequency for the spacer mode in the antenna geometry from 1.6 to 1.9 THz (~15%).

Knowledge of bisphosphonate-related osteonecrosis of the Jawsamong Mexican dentists.

BACKGROUND: Bisphosphonate-related osteonecrosis is an infrequent but potentially serious complication. Its treatment remains complex, and in some cases can be mutilating. Prevention, a correct diagnosis and opportune management are crucial. MATERIAL AND METHODS: A cross-sectional study was made, interviewing 410 dentists with the aim of assessing their knowledge of the subject. RESULTS: Practically all of the dental professionals (99.7%) were found to lack sufficient knowledge of the prevention, diagnosis and management of bisphosphonate-related osteonecrosis. CONCLUSIONS: Actions including increased diffusion in the professional media and inclusion of the subject in training programs are needed in order to enhance the knowledge of bisphosphonate-related osteonecrosis among dentists and thus prevent complications in this group of patients.

Strong coupling in the sub-wavelength limit using metamaterial nanocavities.

The interaction between cavity modes and optical transitions leads to new coupled light-matter states in which the energy is periodically exchanged between the matter states and the optical mode. Here we present experimental evidence of optical strong coupling between modes of individual sub-wavelength metamaterial nanocavities and engineered optical transitions in semiconductor heterostructures. We show that this behaviour is generic by extending the results from the mid-infrared (~10 µm) to the near-infrared (~1.5 µm). Using mid-infrared structures, we demonstrate that the light-matter coupling occurs at the single resonator level and with extremely small interaction volumes. We calculate a mode volume of 4.9 × 10(-4) (λ/n)(3) from which we infer that only ~2,400 electrons per resonator participate in this energy exchange process.

Substrate-modified scattering properties of silicon nanostructures for solar energy applications.

Enhanced light trapping is an attractive technique for improving the efficiency of thin film silicon solar cells. In this paper, we use FDTD simulations to study the scattering properties of silicon nanostructures on a silicon substrate and their application as enhanced light trappers. We find that the scattered spectrum and angular scattering distribution strongly depend on the excitation direction, that is, from air to substrate or from substrate to air. At the dipole resonance wavelength the scattering angles tend to be very narrow compared to those of silicon nanostructures in the absence of a substrate. Based on these properties, we propose a new thin film silicon solar cell design incorporating silicon nanostructures on both the front and back surfaces for enhanced light trapping.

Monolithic metallic nanocavities for strong light-matter interaction to quantum-well intersubband excitations.

We present the design, realization and characterization of strong coupling between an intersubband transition and a monolithic metamaterial nanocavity in the mid-infrared spectral range. We use a ground plane in conjunction with a planar metamaterial resonator for full three-dimensional confinement of the optical mode. This reduces the mode volume by a factor of 1.9 compared to a conventional metamaterial resonator while maintaining the same Rabi frequency. The conductive ground plane is implemented using a highly doped n+ layer which allows us to integrate it monolithically into the device and simplify fabrication.

Nonresonant broadband funneling of light via ultrasubwavelength channels.

Enhancing and funneling light efficiently through deep subwavelength apertures is essential in harnessing light-matter interaction. Thus far, this has been accomplished resonantly, by exciting the structural surface plasmons of perforated nanostructured metal films, a phenomenon known as extraordinary optical transmission. Here, we present a new paradigm structure which possesses all the capabilities of extraordinary optical transmission platforms, yet operates nonresonantly on a distinctly different mechanism. Our proposed platform demonstrates efficient ultrabroadband funneling of optical power confined in an area as small as ∼(λ/500)(2), where optical fields are enhanced, thus exhibiting functional possibilities beyond resonant platforms. We analyze the nonresonant mechanism underpinning such a phenomenon with a simple quasistatic picture, which shows excellent agreement with our numerical simulations.

Strong coupling between nanoscale metamaterials and phonons.

We use split ring resonators (SRRs) at optical frequencies to study strong coupling between planar metamaterials and phonon vibrations in nanometer-scale dielectric layers. A series of SRR metamaterials were fabricated on a semiconductor wafer with a thin intervening SiO(2) dielectric layer. The dimensions of the SRRs were varied to tune the fundamental metamaterial resonance across the infrared (IR) active phonon band of SiO(2) at 130 meV (31 THz). Strong anticrossing of these resonances was observed, indicative of strong coupling between metamaterial and phonon excitations. This coupling is very general and can occur with any electrically polarizable resonance including phonon vibrations in other thin film materials and semiconductor band-to-band transitions in the near to far IR. These effects may be exploited to reduce loss and to create unique spectral features that are not possible with metamaterials alone.

Effect of thin silicon dioxide layers on resonant frequency in infrared metamaterials.

Infrared metamaterials fabricated on semiconductor substrates exhibit a high degree of sensitivity to very thin (as small as 2 nm) layers of low permittivity materials between the metallic elements and the underlying substrate. We have measured the resonant frequencies of split ring resonators and square loops fabricated on Si wafers with silicon dioxide thicknesses ranging from 0 to 10 nm. Resonance features blue shift with increasing silicon dioxide thickness. These effects are explained by the silicon dioxide layer forming a series capacitance to the fringing field across the elements. Resonance coupling to the Si-O vibrational absorption has been observed. Native oxide layers which are normally ignored in numerical simulations of metamaterials must be accounted for to produce accurate predictions.

[Autonomic control and functional condition of suprasegmental structures of the brain in patients with heart rhythm disorders and vasculo-autonomic dystonia]. / Otsenka vegetativnoi reguliatsii i funktsional'nogo sostoianiia nadsegmentarnykh struktur mozga u bol'nykh s narusheniiami ritma serdtsa i vegetativno-sosudistoi distoniei.

A study was made by the method of combination of electroencephalography (EEG) and variational pulsimetry in 157 patients to determine the background vegetative tone and that very tone during conducting functional tests aimed at activating of sympathetic and parasympathetic portions of the nervous system. Criteria have been established characterizing the vegetative tone. Particular features are described of changes in the power of the EEG wave spectra while conducting tests in those groups being different in their baseline vegetative tone. The percentage is estimated of the incidence rate of the cardiac rhythm disturbances in those groups being different in their vegetative tone.

Multiple-channel wavelength conversion by use of engineered quasi-phase-matching structures in LiNbO(3) waveguides.

We report difference frequency generation-based wavelength converters with multiple phase-matching wavelengths that use engineered quasi-phase-matching structures in LiNbO(3) waveguides. Multiple-channel wavelength conversion is demonstrated within the 1.5-mum band and between the 1.3- and 1.5-mum bands. With simultaneous use of M pump wavelengths, these devices can also be used to perform wavelength broadcasting, in which each of N input signals is converted into M output wavelengths.

Multistage dispersion compensator using ring resonators.

A compact, multichannel dispersion-compensating filter is demonstrated with D=-4200 ps/nm, a +/-5-ps group delay ripple, <3-dB loss, and a 4.5-GHz passband width out of a 12.5-GHz free spectral range. We show that multistage designs can achieve a substantial increase in passband width and peak dispersion for a given group-delay ripple compared with single-stage designs. The dispersion-compensation effectiveness was demonstrated in a 320-km, seven-channel nonlinear system simulation for OC48 signals.

High-resolution zero-dispersion wavelength mapping in single-mode fiber.

We present a new noninvasive technique for measuring the spatial variation of the zero-dispersion wavelength (lambda(0)) in single-mode fibers. This technique uses low-power continuous-wave lasers and is simple to implement. When applying this technique to dispersion-shifted fibers, we can resolve subnanometer fluctuations in lambda(0) with a potential spatial resolution of better than 100 m. We also discuss and show the limits of this and other techniques that arise from polarization-mode dispersion in the fibers.

Terahertz emission from electric field singularities in biased semiconductors.

We use electric field singularities in biased metal semiconductor microstructures to enhance the generation of terahertz (THz) radiation from semiconductors. We find that, regardless of the mechanism that is responsible for enhanced THz emission near the anode, singular electric fields near sharp anode features will enhance this emission by as much as an order of magnitude. We show scanning THz measurements of several of these structures and discuss the physical mechanism responsible for this enhanced emission. A new family of more efficient terahertz emitters based on these effects can be designed that will improve the dynamic range of THz imaging and spectroscopy systems.