Search results for "tunable"

Real-time measurements of Volcanic Gases based by Infrared Spectroscopy

2014

Near-infrared Tunable Diode Lasers have recently found increased usage in atmospheric chemistry and air monitoring research, but applications in Volcanology are still limited to a few examples. The Tunable Diode Laser Spectroscopy technique (TDLS) relies on measuring the absorbance at specific wavelengths due to the absorption of IR radiation by a target gas. Here, we report on the application of the GasFinder 2.0, a commercial infrared laser-receiver unit operating in the 1.3-1.7 m wavelength range, to measuring CO2 concentrations and fluxes in volcanic gas emissions. Our field tests were conducted at Campi Flegrei volcano (near Pozzuoli, Southern Italy), where the GasFinder was used (duri…

Frequency-modulation spectroscopy with blue diode lasers

2000

Frequency-modulation spectroscopy provides ultrasensitive absorption measurements. The technique is especially adaptable to diode lasers, which can be modulated easily, and has been used extensively in the near-infrared and infrared spectral regions. The availability of blue diode lasers now means that the accessible wavelength region can be increased. We successfully demonstrate wavelength-modulation spectroscopy and two-tone frequency-modulation spectroscopy for the weak second resonance line of potassium at 404.8 nm and for the transition at 405.8 nm in lead, starting from the thermally populated 6p(2) P-3(2) metastable level, information on the modulation parameters is obtained with a f…

Subpicosecond Laser Spectroscopy of Blue-Light-Induced Absorption in KNbO3 and LiNbO3

2000

Pulses of 427-nm light from am amplified Ti:sapphire frequency-doubled laser are absorbed in two-photon band-gap excitations of KNbO3 and LiNbO3. Induced absorption spectra measured in the visible and recently extended in the infrared have been recorded as a function of delay from 0 to 250 ps after two-photon blue excitation. Samples include stoichiometric as well as congruent LiNbO3. Comparison is made to transient absorption in the nanosecond and longer time range induced by electron pulses of~10 ns width and 270 keV energy. Parts of the absorption can be attributed to bound and free polarons, including the intrinsic electron polaron.

Violet Diode Laser in Time-Resolved Stored-Ion Spectroscopy

2004

Lifetime measurements of the metastable 3d D-2(3/2) level in singly charged calcium were performed using the newly developed violet diode laser operated in an external cavity arrangement. The laser was employed on stored ions at the CRYRING facility to optically pump the resonance line at 397 nm. In combination with laser probing at 866 nm this detection scheme gave the possibility to record the lifetime of this level. which has a radiative lifetime of about 1 s.

Tunable radical scavenging activity of carbonaceous structures and their anti-oxidant behaviour in polymer based nanocomposites

2017

Introduction: Carbon nanotubes (CNTs), due to their electronic properties, show radical scavenging activity toward the radical formed during the degradation processes of polymeric materials. In this work, we propose a novel strategy to control the CNTs anti-oxidant features through the application of an ultrasound treatment (us). Materials and Methods: Ultra high molecular weight polyethylene (UHMWPE); multi-walled carbon nanotubes (CNTs); CNTs have been sonicated at room temperature for different time intervals. Nanocomposites have been prepared though hot compaction and fully characterized. Results: The content of CNTs structural defects, evaluated through Raman-spectroscopy, increases wi…

REAL-TIME MEASUREMENT OF VOLCANIC GASES BASED ON INFRARED SPECTROSCOPY

The interpretation of volcanic gas datasets offers key information to build/validate geological models relevant to a variety of volcanic processes and behaviours, including eruptions. Major efforts have therefore been spent in recent years to improve our ability to measure volcanic gas compositions and fluxes. In the last decades, near-infrared room-temperature diode lasers, though in an experimental phase, are finding applications in volcanic gas studies. In this PhD dissertation, I use the GasFinder 2.0, a commercial tunable diode infrared laser transmitter-receiver unit, operating in the 1.3-1.7 m wavelength range, in the attempt to measure CO2 mixing ratios and fluxes in volcanic gas e…

Céramiques diélectriques commandables pour applications micro-ondes : composites à base de titanate de baryum-strontium et d'un oxyde non ferroélectr…

2001

Since the last decades, dielectric ceramics have been considered as attractive for microwave applications as tunable dielectric resonators or phase shifters. For that, ceramic devices should be tunable – change in dielectric constant with applied voltage- with moderate to low dielectric constant (30 to 1000) and loss tangent as low as possible. To reconcile these properties, composite ceramics based on Ba0.6Sr0.4TiO3 (BSTO) and a non-ferroelectric oxide with a low dielectric constant (MgTiO3 or MgO) were synthesised. The aim of this study was to correlate the microstructure with the dielectric properties, especially the Curie temperature and the dielectric relaxation phenomena.Ceramics with…

Automated detection and localization system of myocardial infarction in single-beat ECG using Dual-Q TQWT and wavelet packet tensor decomposition

2020

Background and objective. It is challenging to conduct real-time identification of myocardial infarction (MI) due to artifact corruption and high dimensionality of multi-lead electrocardiogram (ECG). In the present study, we proposed an automated single-beat MI detection and localization system using dual-Q tunable Q-factor wavelet transformation (Dual-Q TQWT) denoising algorithm. Methods. After denoising and segmentation of ECG, a fourth-order wavelet tensor (leads × subbands × samples × beats) was constructed based on thediscretewavelet packet transform (DWPT), to represent the features considering the information of inter-beat, intra-beat, inter-frequency, and inter-lead. To reduce the t…

FLUMO: FLexible Underwater MOdem

2019

The last years have seen a growing interest in underwater acoustic communications because of its applications in marine research, oceanography, marine commercial operations, the offshore oil industry and defense. High-speed communication in the underwater acoustic channel has been challenging because of limited bandwidth, extended multipath, refractive properties of the medium, severe fading, rapid time variation and large Doppler shifts. In this paper, we show an implementation of a flexible Software-Defined Acoustic (SDA) underwater modem, where modulation parameters are completely tunable to optimize performance. In particular, we develop the system architecture following two key ideas. …

Volcanic CO_2 detection with a DFM/OPA-based lidar

2015

The DFM/OPA-based lidar BILLI was used to investigate the volcanic plume released by the hydrothermal vent of Pisciarelli, in the Campi Flegrei volcano. BILLI remotely measured CO2 concentrations in cross-sections of the nearvent plume using the differential absorption technique. To our knowledge, this is the first example of lidar-based measurement of volcanic CO2 . The spatial resolution was 1.5 m and the temporal resolution 20 s. © 2015 Optical Society of America.