397 research outputs found
Programming scale-free optics in disordered ferroelectrics
Using the history-dependence of a dipolar glass hosted in a
compositionally-disordered lithium-enriched potassium-tantalate-niobate
(KTN:Li) crystal, we demonstrate scale-free optical propagation at tunable
temperatures. The operating equilibration temperature is determined by previous
crystal spiralling in the temperature/cooling-rate phase-space
Evidence of double-loop hysteresis in disordered ferroelectric crystal
Double-loop electric-field vs polarization hysteresis is investigated in a depoled compositionally disordered lithium-enriched potassium tantalate niobate crystal. Comparing electro-optic response and dielectric spectroscopy indicates that the anomalous response occurs for those temperatures in which the sample also manifests a temperature hysteresis in the low-frequency dielectric function. An electric-field hysteresis at concurrent temperatures suggests an underlying role of reorienting mesoscopic polar regions that accompany the nonergodic phase. Published under license by AIP Publishing
Photorefractive light needles in glassy nanodisordered KNTN
We study the formation of 2D self-trapped beams in nanodisordered potassium-sodium-tantalate-niobate (KNTN) cooled below the dynamic glass transition. Supercooling is shown to accelerate the photorefractive response and enhance steady-state anisotropy. Effects in the excited state are attributed to the anomalous slim-loop polarization curve typical of relaxors dominated by non-interacting polar-nano-regions
Observation of an intrinsic nonlinearity in the electro-optic response of freezing relaxors ferroelectrics
We demonstrate an electro-optic response that is linear in the
amplitude but independent of the sign of the applied electric field. The
symmetry-preserving linear electro-optic effect emerges at low applied
electric fields in freezing nanodisordered KNTN above the dielectric peak
temperature, deep into the nominal paraelectric phase. Strong temperature
dependence allows us to attribute the phenomenon to an anomalously
reduced thermal agitation in the reorientational response of the underlying
polar-nanoregions
Line-Shaped Illumination: A Promising Configuration for a Flexible Two-Photon Microscopy Setup
An innovative two-photon microscope exploiting a line-shaped illumination has been recently devised and then implemented. Such configuration allows to carry out a real-time detection by means of standard CCD cameras and is able to maintain the same resolution as commonly used point-scanning devices, thus overcoming what is usually regarded as the main limitation of linescanning microscopes. Here, we provide an overview of the applications in which this device has been tested and has proved to be a flexible and efficient tool, namely imaging of biological samples, in-depth sample reconstruction, two-photon spectra detection, and dye cross-section measurements. These results demonstrate that the considered setup is promising for future developments in many areas of research and applications
Observation of electro-activated localized structures in broad area VCSELs
We demonstrate experimentally the electro-activation of a localized optical
structure in a coherently driven broad-area vertical-cavity surface-emitting
laser (VCSEL) operated below threshold. Control is achieved by
electro-optically steering a writing beam through a pre-programmable switch
based on a photorefractive funnel waveguide.Comment: 5 Figure
Nonlinear optics in a high-index of refraction material
Nonlinear response in a material increases with its index of refraction as
. Commonly, 1 so that diffraction, dispersion, and chromatic
walk-off limit nonlinear scattering. Ferroelectric crystals with a periodic 3D
polarization structure overcome some of these constraints through versatile
Cherenkov and quasi-phase-matching mechanisms. Three-dimensional
self-structuring can also lead to a giant broadband refraction
\cite{DiMei2018}. We here perform second-harmonic-generation experiments in
KTN:Li with . Enhanced response causes wavelength conversion to occur in
the form of bulk Cherenkov radiation without diffraction and chromatic
walk-off, even in the presence of strong wave-vector mismatch and highly
focused beams. The process occurs with an arbitrarily wide spectral acceptance,
more than 100 nm in the near infrared spectrum, an ultra-wide angular
acceptance, up to , with no polarization selectivity, and can
be tuned to allow bulk supercontinuum generation. Results pave the way to
highly efficient versatile and adaptable nonlinear optical devices with the
promise of single-photon-to-single-photon nonlinear optics.Comment: 9 pages, 5 figure
Nitrogen enrichment in macroalgae following mass coral mortality
Scleractinian corals are engineers on coral reefs that provide both structural complexity as habitat and sustenance for other reef-associated organisms via the release of organic and inorganic matter. However, coral reefs are facing multiple pressures from climate change and other stressors, which can result in mass coral bleaching and mortality events. Mass mortality of corals results in enhanced release of organic matter, which can cause significant alterations to reef biochemical and recycling processes. There is little known about how long these nutrients are retained within the system, for instance, within the tissues of other benthic organisms. We investigated changes in nitrogen isotopic signatures (δ15N) of macroalgal tissues (a) ~ 1 year after a bleaching event in the Seychelles and (b) ~ 3 months after the peak of a bleaching event in Mo’orea, French Polynesia. In the Seychelles, there was a strong association between absolute loss in both total coral cover and branching coral cover and absolute increase in macroalgal δ15N between 2014 and 2017 (adjusted r2 = 0.79, p = 0.004 and adjusted r2 = 0.86, p = 0.002, respectively). In Mo’orea, a short-term transplant experiment found a significant increase in δ15N in Sargassum mangarevense after specimens were deployed on a reef with high coral mortality for ~ 3 weeks (p < 0.05). We suggest that coral-derived nutrients can be retained within reef nutrient cycles, and that this can affect other reef-associated organisms over both short- and long-term periods, especially opportunistic species such as macroalgae. These species could therefore proliferate on reefs that have experienced mass mortality events, because they have been provided with both space and nutrient subsidies by the death and decay of corals. © 2021, The Author(s)
Aging solitons in photorefractive dipolar glasses
We study experimentally the aging of optical spatial solitons in a dipolar glass hosted by a nanodisordered sample of photorefractive potassium-sodium-tantalate-niobate (KNTN). As the system ages, the waves erratically explore varying strengths of the nonlinear response, causing them to break up and scatter. We show that this process can still lead to solitons, but in a generalized form for which the changing response is compensated by changing the normalized wave size and intensity so as to maintain fixed the optical waveform
Anti-diffracting beams through the diffusive optical nonlinearity
Anti-diffraction is a theoretically predicted nonlinear optical
phenomenon that occurs when a light beam spontaneously focalizes independently of its intensity. We observe anti-diffracting beams supported by the peak-intensity-independent diffusive nonlinearity that are able to shrink below their diffraction-limited size in photorefractive lithium-enriched potassium-tantalate-niobate (KTN:Li)
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