Search results for "Pulse"
showing 10 items of 1508 documents
Comparison of Single Event Transients Generated at Four Pulsed-Laser Test Facilities-NRL, IMS, EADS, JPL
2012
Four pulsed-laser single-event effects systems, differing in wavelength and pulse width, were used to generate single event transients in a large-area silicon photodiode and an operational amplifier (LM124) to determine how transient amplitude and charge collection varied among the different systems. The optical wavelength and the focused spot size are the primary factors influencing the resultant charge density profile. In the large-area photodiode the transients can be distorted by high charge-injection densities that occur for tightly focused, higher energy optical pulses. When the incident laser-pulse energies are corrected for reflection losses and photon efficiency, with collection de…
Mixed-Mode Operation of Hybrid Phase-Change Nanophotonic Circuits
2016
Phase change materials (PCMs) are highly attractive for nonvolatile electrical and all-optical memory applications because of unique features such as ultrafast and reversible phase transitions, long-term endurance, and high scalability to nanoscale dimensions. Understanding their transient characteristics upon phase transition in both the electrical and the optical domains is essential for using PCMs in future multifunctional optoelectronic circuits. Here, we use a PCM nanowire embedded into a nanophotonic circuit to study switching dynamics in mixed-mode operation. Evanescent coupling between light traveling along waveguides and a phase-change nanowire enables reversible phase transition b…
Single crystal-like thin films of blue bronze
2021
Abstract Pulsed laser deposition technique was employed to grow thin films of K 0.3 M o O 3 on A l 2 O 3 (1-102) and S r T i O 3 (510) substrates. Structural and imaging characterization revealed good quality films with well oriented grains of few microns in length. Both non-selective (transport) and order-selective (femtosecond pump-probe spectroscopy) probes revealed charge density wave properties that are very close to those of the single crystals. The films exhibit metal-semiconductor phase transition in resistivity, pump-probe data show phase transition at the same temperature as the single crystal and the threshold for the photo-induced phase transition is approximately the same as in…
Correlation between in situ structural and optical characterization of the semiconductor-to-metal phase transition of VO2 thin films on sapphire
2020
A detailed structural investigation of the semiconductor-to-metal transition (SMT) in vanadium dioxide thin films deposited on sapphire substrates by pulsed laser deposition was performed by in situ temperature-dependent X-ray diffraction (XRD) measurements. The structural results are correlated with those of infrared radiometry measurements in the SWIR (2.5-5 μm) and LWIR (8-10.6 μm) spectral ranges. The main results indicate a good agreement between XRD and optical analysis, therefore demonstrating that the structural transition from monoclinic to tetragonal phases is the dominating mechanism for controlling the global properties of the SMT transition. The picture that emerges is a SMT tr…
Interface evolution during magnetic pulse welding under extremely high strain rate collision: mechanisms, thermomechanical kinetics and consequences
2020
Abstract Magnetic pulse welding enables to produce perplexing interfacial morphologies due to the complex material response during the high strain rate collision. Thus, a thermomechanical model is used in this study to investigate the formation mechanism of the wake, vortex, swirling and mesoscale cavities with the increase of the impact intensity at the interface. The formation of these interfacial features are difficult to characterize by insitu methods, thus the origin of phenomena still remain a subject of open discussion. Our studies identify the governing mechanisms and the associated thermomechanical kinetics, which are responsible for the formation mechanism of interfacial features.…
Stealth dicing with ultrafast Bessel beams with engineered transverse profiles
2017
International audience; We investigate high-speed glass cleaving with ultrafast laser beams with engineered transverse intensity profile. We achieve accuracy of ~ 1 µm at 25 mm/s and drastically enhance cleavability compared to standard Bessel beams.
Review of the PEA Method for Space Charge Measurements on HVDC Cables and Mini-Cables
2019
This review takes into account articles and standards published in recent years concerning the application of the Pulsed Electro Acoustic (PEA) method for space charge measurement on High Voltage Direct Current (HVDC) cables and mini-cables. Since the 80s, the PEA method has been implemented for space charge measurements on flat specimens in order to investigate space charge phenomena and to evaluate the ageing of dielectrics. In recent years, this technique has been adapted to cylindrical geometry. Several studies and experiments have been carried out on the use of the PEA method for full size cables and HVDC cable models. The experiments have been conducted using different arrangements of…
Plasma sloshing in pulse-heated solar and stellar coronal loops
2016
There is evidence that coronal heating is highly intermittent, and flares are the high energy extreme. The properties of the heat pulses are difficult to constrain. Here hydrodynamic loop modeling shows that several large amplitude oscillations (~ 20% in density) are triggered in flare light curves if the duration of the heat pulse is shorter that the sound crossing time of the flaring loop. The reason is that the plasma has not enough time to reach pressure equilibrium during the heating and traveling pressure fronts develop. The period is a few minutes for typical solar coronal loops, dictated by the sound crossing time in the decay phase. The long period and large amplitude make these os…
Flashing light emitting diodes (LEDs) induce proteins, polyunsaturated fatty acids and pigments in three microalgae
2020
As the periodic emission of light pulses by light emitting diodes (LEDs) is known to stimulate growth or induce high value biocompounds in microalgae, this flashing light regime was tested on growth and biochemical composition of the microalgae Nannochloropsis gaditana, Koliella antarctica and Tetraselmis chui. At low flashing light frequencies (e.g., 5 and 50 Hz, Duty cycle = 0.05), a strain-dependent growth inhibition and an accumulation of protein, polyunsaturated fatty acids, chlorophyll or carotenoids (lutein, β-carotene, violaxanthin and neoxanthin) was observed. In addition, a 4-day application of low-frequency flashing light to concentrated cultures increased productivities of eicos…
Rigid Core and Flexible Terminus
2012
The structure of the major light-harvesting chlorophyll a/b complex (LHCII) was analyzed by pulsed EPR measurements and compared with the crystal structure. Site-specific spin labeling of the recombinant protein allowed the measurement of distance distributions over several intra- and intermolecular distances in monomeric and trimeric LHCII, yielding information on the protein structure and its local flexibility. A spin label rotamer library based on a molecular dynamics simulation was used to take the local mobility of spin labels into account. The core of LHCII in solution adopts a structure very similar or identical to the one seen in crystallized LHCII trimers with little motional freed…