Search results for "SPECTRA"

Direct determination of polymerised triacylglycerides in deep-frying vegetable oil by near infrared spectroscopy using Partial Least Squares regressi…

2012

Abstract A green method for the determination of polymerised triacylglyceride (PTG) in deep-frying vegetable oils of different botanic origin has been developed employing near infrared (NIR) spectroscopy and Partial Least Squares (PLS) regression. Four different types of oil were heated during several hours, with and without the addition of foodstuff. NIR transmission spectra were obtained directly from sample aliquots stored in glass vials, thus avoiding the consumption of solvents and minimising waste generation. Variables employed for building the PLS models were selected applying interval PLS (iPLS) as well as Uninformative Variable Elimination-PLS (UVE-PLS). A global PLS model using sp…

The closure of the numerical range of an operator as spectral set

1964

Approximation properties of q-Kantorovich-Stancu operator

2015

In this paper we study some properties of Kantorovich-type generalizations of the q-Stancu operators. We obtain some approximation properties for these operators, estimating the rate of convergence by using the first and second modulus of continuity. Also, we investigate the statistical approximation properties of the q-Kantorovich-Stancu operators using the Korovkin-type statistical approximation theorem.

Radiation hardening of Rare-Earth doped fiber amplifiers

2012

We investigated the radiation hardening of optical fiber amplifiers operating in space environments. Through a real-time analysis in active configuration, we evaluated the role of Ce in the improvement of the amplifier performance against ionizing radiations. Ce-codoping is an efficient hardening solution, acting both in the limitation of defects in the host glass matrix of RE-doped optical fibers and in the stabilization of lasing properties of the Er3+-ions. On the one hand, in the nearinfrared region, radiation induced attenuation measurements show the absence of radiation induced P-related defect species in host glass matrix of the Ce-codoped active fibers; on the other hand, in the Ce-…

Linear and nonlinear fiber propagation of partially coherent fields exhibiting temporal correlations

2019

International audience; Using ultrafast photonic first-order differentiator applied on a partially coherent field, we report the generation of two correlated temporal waveforms and study their correlation properties upon linear and nonlinear propagation along the two orthogonal polarization axis of a dispersive optical fiber. Temporal correlations are maintained in linear propagation whereas Kerr nonlinearity generates anti-correlated temporal intensity patterns for both partially and uncorrelated fields. Experiments are in close agreement with the theoretical analysis.

Tunable microwave photonic filter based on chirped fiber gratings working with a single optical carrier at constant wavelength

2007

This paper presents a tunable transversal filter working with a single optical carrier at constant wavelength. The filter consists of a set of chirped gratings whose time delay is tuned with respect to the emission wavelength of a fiber laser by a piezoelectric actuator; extra lengths of fiber are inserted in the filter arms in order to avoid interferences between signals reflected in different gratings. Two and three taps filters are experimentally demonstrated, the filters transfer function is electronically tuned within the free spectral range.

Ultraviolet-visible light-induced solarisation in silica-based optical fibres for indoor solar applications

2021

Abstract The transmission performances of pure- and doped-silica (a-SiO2) optical fibres are compared during the exposure to a high-power broadband light source approximating the solar spectrum. From the Gaussian decomposition of the attenuation spectra, we found that Al- and P-doped fibres show a fast solarisation effect which leads to transmission degradation in the ultraviolet-visible range. Similarly, Ge-doped fibres undergo photoinduced colour-centre formation which, however, does not prevent visible-light propagation. One of the two tested pure-silica fibres results completely unaffected by light exposure whereas the other shows an absorption band probably due to the presence of chlor…

Design of double-tapered fibers for tailoring the acousto-optic spectral response

2016

A model to shape the spectral response of acousto-optic devices based on tapered fibers is reported. A double-tapered structure was designed in order to obtain a flat attenuation response with 34 nm bandwidth.

Novel spectra in the supercontinuum generation with applications in the biodiversity conservation

2014

This paper presents some spectra of the supercontinuum generation obtained with microstructured fibers and tapered fiber devices excited with quasi-continuous pumps. These spectra are part of a group (collection) of multiple configurations that were studied and evaluated by our working group, and that could be very useful in LIDAR as well as bio-imaging applications. This work is limited to present some spectra that could be useful in applications of biodiversity conservation. The prototypes for specific applications will be evaluated in future research.

Improvement of two-dimensional structured illumination microscopy with an incoherent illumination pattern of tunable frequency.

2018

In two-dimensional structured illumination microscopy (2D-SIM), high-resolution images with optimal optical sectioning (OS) cannot be obtained simultaneously. This tradeoff can be overcome by using a tunable-frequency 2D-SIM system and a proper reconstruction method. The goal of this work is twofold. First, we present a computational approach to reconstruct optical-sectioned images with super-resolution enhancement (OS-SR) by using a tunable SIM system. Second, we propose an incoherent tunable-frequency 2D-SIM system based on a Fresnel biprism implementation. Integration of the proposed computational method with this tunable structured illumination (SI) system results in a new 2D-SIM system…