Suppression of four-wave mixing in hot rubidium vapor using ladder scheme Raman absorption

We experimentally investigate the effectiveness of four-wave mixing suppression in a double-interaction scheme by introducing an additional ladder-type two-photon Raman absorption resonance for one of the optical fields. We propose several possible interaction configurations involving either one or two isotopes of Rb and experimentally demonstrate the possibility of efficient four-wave mixing suppression in both electromagnetically induced transparency and far-detuned Raman cases. (C) 2017 Optical Society of Americ

Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts

Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (similar to 10-1000 s) GW emission associated with the accretion disk of a collapsed star or with its protoneutron star remnant. Using data from LIGO\u27s fifth science run, and GRB triggers from the Swift experiment, we perform a search for unmodeled long-lived GW transients. Finding no evidence of GW emission, we place 90% confidence-level upper limits on the GW fluence at Earth from long GRBs for three waveforms inspired by a model of GWs from accretion disk instabilities. These limits range from F \u3c 3.5 ergs cm(-2) to F \u3c 1200 ergs cm(-2), depending on the GRB and on the model, allowing us to probe optimistic scenarios of GW production out to distances as far as approximate to 33 Mpc. Advanced detectors are expected to achieve strain sensitivities 10X better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs

Hydrogeological monitoring of karst activity based on regime observations in the territory of karst lakes

This article shows that the most sensitive indicator of local and regional karst activity in territories of apparent karst processes is the behaviour of karst lakes. The authors propose a hydrogeological monitoring methodology for the karst process based on the phase-measuring geoelectric control method in the coastal zone of karst lakes. The geoelectric current control of hydrogeological changes in the medium at local levels uses a multi-frequency vertical electric sounding combined with a phase-measuring method of registering the geoelectric signal. These proven methods permit to distinguish variations of spatial parameters and the electric conductivity of several layers at a time. Moreover, they significantly increase the noise resistance and sensitivity of the measuring system. An adaptive algorithm function of the measuring complex for geoelectric monitoring of karst lakes’ coastal zones was developed to control the operation of facilities and data collection systems. Based on an example of a lake where karst processes are active, the key zones of hydrogeological control were identified depending on karst manifestations. The research confirmed the possibility of local and regional monitoring of the development and forecasting of destructive karst-suffosion processes based on hydrogeological regime observations of karst lakes

Tunable optical properties of transition metal dichalcogenide nanoparticles synthesized by femtosecond laser ablation and fragmentation

International audienceManipulation of resonant dielectric nanostructures is of paramount importance for next-generation photonic devices. Traditionally, researchers use two-dimensional or phase-change materials for this purpose. However, the former leads to small efficiency, while the latter lacks continuous changes. Here, we provide an alternative approach through laser-induced modification. Specifically, via a laser ablation process we synthesized molybdenum disulfide (MoS 2) nanoparticles (NPs), the composition of which we then controlled through laser fragmentation. It causes a transformation of MoS 2 into its oxide MoO 3Àx , which, in turn, results in pronounced modification of the optical response, owing to a large difference between their optical constants. In addition, laser-fragmented NPs have a several times larger photothermal response, compared to the original MoS 2 and classical silicon NPs. Thus, our MoS 2-based laser-tunable NPs open up a new perspective for resonant nanophotonics, in particular, photothermal therapy

Optical Constants and Structural Properties of Epitaxial MoS2 Monolayers

Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality flakes with a size limited to a few micrometers, the latter gives large-area layers but with a nonuniform surface resulting from multiple defects and randomly oriented domains. The use of epitaxy growth can produce continuous, crystalline and uniform films with fewer defects. Here, we present a comprehensive study of the optical and structural properties of a single layer of MoS2 synthesized by molecular beam epitaxy (MBE) on a sapphire substrate. For optical characterization, we performed spectroscopic ellipsometry over a broad spectral range (from 250 to 1700 nm) under variable incident angles. The structural quality was assessed by optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy through which we were able to confirm that our sample contains a single-atomic layer of MoS2 with a low number of defects. Raman and photoluminescence spectroscopies revealed that MBE-synthesized MoS2 layers exhibit a two-times higher quantum yield of photoluminescence along with lower photobleaching compared to CVD-grown MoS2, thus making it an attractive candidate for photonic applications

Optical Constants of Chemical Vapor Deposited Graphene for Photonic Applications

Graphene is a promising building block material for developing novel photonic and optoelectronic devices. Here, we report a comprehensive experimental study of chemical-vapor deposited (CVD) monolayer graphene’s optical properties on three different substrates for ultraviolet, visible, and near-infrared spectral ranges (from 240 to 1000 nm). Importantly, our ellipsometric measurements are free from the assumptions of additional nanometer-thick layers of water or other media. This issue is critical for practical applications since otherwise, these additional layers must be included in the design models of various graphene photonic, plasmonic, and optoelectronic devices. We observe a slight difference (not exceeding 5%) in the optical constants of graphene on different substrates. Further, the optical constants reported here are very close to those of graphite, which hints on their applicability to multilayer graphene structures. This work provides reliable data on monolayer graphene’s optical properties, which should be useful for modeling and designing photonic devices with graphene

Chemical Synapses without Synaptic Vesicles: Purinergic Neurotransmission through a CALHM1 Channel-mitochondrial Signaling Complex

Conventional chemical synapses in the nervous system involve a presynaptic accumulation of neurotransmitter-containing vesicles, which fuse with the plasma membrane to release neurotransmitters that activate postsynaptic receptors. In taste buds, type II receptor cells do not have conventional synaptic features but nonetheless show regulated release of their afferent neurotransmitter, ATP, through a large-pore, voltage-gated channel, CALHM1. Immunohistochemistry revealed that CALHM1 was localized to points of contact between the receptor cells and sensory nerve fibers. Ultrastructural and super-resolution light microscopy showed that the CALHM1 channels were consistently associated with distinctive, large (1- to 2-μm) mitochondria spaced 20 to 40 nm from the presynaptic membrane. Pharmacological disruption of the mitochondrial respiratory chain limited the ability of taste cells to release ATP, suggesting that the immediate source of released ATP was the mitochondrion rather than a cytoplasmic pool of ATP. These large mitochondria may serve as both a reservoir of releasable ATP and the site of synthesis. The juxtaposition of the large mitochondria to areas of membrane displaying CALHM1 also defines a restricted compartment that limits the influx of Ca2+ upon opening of the nonselective CALHM1 channels. These findings reveal a distinctive organelle signature and functional organization for regulated, focal release of purinergic signals in the absence of synaptic vesicles