Search results for "Optoelectronics"
showing 10 items of 2306 documents
Radiation tolerant fiber Bragg gratings for high temperature monitoring at MGy dose levels
2014
International audience; We report a method for fabricating fiber Bragg gratings (FBG) resistant to very severe environments mixing high radiation doses (up to 3 MGy) and high temperatures (up to 230 degrees C). Such FBGs have been written in two types of radiation resistant optical fibers (pure-silica and fluorine-doped cores) by exposures to a 800 nm femtosecond IR laser at power exceeding 500 mW and then subjected to a thermal annealing treatment of 15 min at 750 degrees C. Under radiation, our study reveals that the radiation induced Bragg wavelength shift (BWS) at a 3 MGy dose is strongly reduced compared to responses of FBGs written with nonoptimized conditions. The BWS remains lower t…
Recent improvements in PbO2 nanowire electrodes for lead-acid battery
2015
Abstract Lead oxide nanowires are an attractive alternative to conventional pasted electrodes, owing to their high surface area leading to high specific energy batteries. Here, we report the performance of template electrodeposited PbO 2 nanowires used as positive electrodes. Nanostructured electrodes were tested at constant charge/discharge rate from 2 C to 10 C, with a cut-off potential of 1.2 V and discharge depth up to 90% of the gravimetric charge. These new type of electrodes are able to work at very high C-rate without fading, reaching an efficiency of about 90% with a very good cycling stability. In particular, after an initial stabilization, a specific capacity of about 200 mAh g −…
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
2016
Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source which relies on tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photo-induced spin currents, the inverse spin-Hall effect an…
Terahertz electrical writing speed in an antiferromagnetic memory
2018
The speed of writing of state-of-the-art ferromagnetic memories is physically limited by an intrinsic gigahertz threshold. Recently, realization of memory devices based on antiferromagnets, in which spin directions periodically alternate from one atomic lattice site to the next has moved research in an alternative direction. We experimentally demonstrate at room temperature that the speed of reversible electrical writing in a memory device can be scaled up to terahertz using an antiferromagnet. A current-induced spin-torque mechanism is responsible for the switching in our memory devices throughout the 12-order-of-magnitude range of writing speeds from hertz to terahertz. Our work opens the…
Surface plasmon interference fringes in back-reflection
2010
We report the experimental observation of surface plasmon polariton (SPP) interference fringes with near-unity visibility and half-wavelength periodicity obtained in back reflection on a Bragg mirror. The presented method based on leakage radiation microscopy (LRM) represents an alternative solution to optical near-field analysis and opens new ways for the quantitative analysis of SPP fringes. With LRM we investigate various SPP interference patterns and analyze the high reflectivity of Bragg mirror in comparison with theoretical models.
Influence of spectral composition on the temperature coefficients of solar cells from Elkem Solar
2014
The temperature coefficients of solar cells from two different feedstocks — a compensated silicon, the Elkem Solar Silicon (ESS®), and polysilicon - under full and selective parts of the light spectrum are presented based on results obtained using a AAA sun simulator. These results are of particular interest in understanding the possible causes behind the better temperature coefficients usually observed for ESS® compared to polysilicon solar cells when measured with a full AM1.5 spectrum. The optical filtered lights from four different regions of the spectrum have been used to examine the influence of temperature coefficients on the spectral composition. ESS® solar cells showed considerable…
Theoretical analysis of the optimum energy band gap of semiconductors for fabrication of solar cells for applications in higher latitudes locations
2005
In this work some results of theoretical analysis on the selection of optimum band gap semiconductor absorbers for application in either single or multijunction (up to five junctions) solar cells are presented. For calculations days have been taken characterized by various insolation and ambient temperature conditions defined in the draft of the IEC 61836 standard (Performance testing and energy rating of terrestrial photovoltaic modules) as a proposal of representative set of typical outdoor conditions that may influence performance of photovoltaic devices. Besides various irradiance and ambient temperature ranges, these days additionally differ significantly regarding spectral distributio…
Chalcopyrite Semiconductors for Quantum Well Solar Cells
2011
We explore here the possibilities of using highly absorbing chalcopyrite semiconductors of the type Cu(In,Ga)Se2 in a quantum well solar cell structure. Thin alternating layers of 50 nm CuInSe2 and CuGaSe2 were grown epitaxially on a GaAs(100) substrate employing metalorganic vapor phase epitaxy. The optical properties of a resulting structure of three layers were investigated by photoluminescence and photoreflectance, indicating charge carrier confinement ∗To whom correspondence should be addressed †Helmholtz-Zentrum Berlin ‡Universidad Politecnica de Madrid ¶University of Illinois §University of Jyvaskyla ‖Current address: Universitat des Saarlandes, Uni Campus, Gebaude A5.1, 66123 Saarbr…
Fabrication and Characterization of Polymeric Optical Waveguides Using Standard Silicon Processing Technology
2005
We report the fabrication and characterization of a rib polymeric waveguide having a thick layer of oxidized porous silicon as an innovative solution for the lower cladding. The waveguide was fabricated using standard silicon substrates and Si-based technology. The multimodal guiding structure has a polymethylmetacrylate (PMMA) core and the innovative lower cladding was obtained by thermal oxidation of a porous silicon layer. The waveguide does not have the upper cladding. Propagation loss measurements were performed at 1.48 /spl mu/m using the cut-back method. We obtained propagation loss of about 1.7 dB/cm, confirming the possibility to use the porous silicon oxide as the lower cladding l…
A fully planar approach to the construction of X-Ray microcalorimeters with doped Germanium sensors
2008
We have investigated a fully planar technology for the development of arrays of X-ray microcalorimeters with doped germanium thermal sensor. We describe the proposed approach and show promising results obtained with the deep etching of germanium, the most critical step of the whole process.