Search results for "Optoelectronics"
showing 10 items of 2306 documents
Enhancing single-parameter quantum charge pumping in carbon-based devices
2011
We present a theoretical study of quantum charge pumping with a single ac gate applied to graphene nanoribbons and carbon nanotubes operating with low resistance contacts. By combining Floquet theory with Green's function formalism, we show that the pumped current can be tuned and enhanced by up to two orders of magnitude by an appropriate choice of device length, gate voltage intensity and driving frequency and amplitude. These results offer a promising alternative for enhancing the pumped currents in these carbon-based devices.
Towards combined multispectral, FLIM and Raman imaging for skin diagnostics
2020
To explore challenges for further improvement of diagnostic performance, a project aimed at development of technology for tri-modal skin imaging by combining multispectral, fluorescence lifetime and Raman band imaging was initiated. In this study, each of the mentioned imaging modalities has been preliminary tested and updated. Four different multispectral imaging devices were tested on color standards. Picosecond laser-excited fluorescence lifetime imaging equipment was examined on ex-vivo skin samples. Finally, a new Raman spectroscopy setup with 785 nm laser was launched and tested on cell cultures and ex-vivo skin. Advantages and specific features of the tri-modal skin imaging are discu…
Fluorescence and spin properties of defects in single digit nanodiamonds
2009
International audience; This article reports stable photoluminescence and high-contrast optically detected electron spin resonance (ODESR) from single nitrogen-vacancy (NV) defect centers created within ultrasmall, disperse nanodiamonds of radius less than 4 nm. Unexpectedly, the efficiency for the production of NV fluorescent defects by electron irradiation is found to be independent of the size of the nanocrystals. Fluorescence lifetime imaging shows lifetimes with a mean value of around 17 ns, only slightly longer than the bulk value of the defects. After proper surface cleaning, the dephasing times of the electron spin resonance in the nanocrystals approach values of some microseconds, …
Self-pumped phase conjugation in a BaTiO3:Rh waveguide
2002
We present a self-pumped phase conjugator originated by self-bending of the incident beam at λ = 515 nm in a BaTiO3:Rh waveguide elaborated by three successive He+ ion implantations. Phase conjugate reflectivity reached is 28 %.
Internal photoemission in solar blind AlGaN Schottky barrier photodiodes
2005
We have analyzed the photoresponse of solar blind AlGaN Schottky barrier photodiodes below the alloy band gap energy, in the 3.5-4.5 eV range, and we show that it is dominated by internal photoemission. The n-type Schottky barrier height is shown to increase linearly with the band gap energy of the AlGaN alloy. The amplitude of the internal photoemission signal is about 20 times smaller than the value given by the Fowler theory based on a free electron model. We explain this result by taking into account the interband transitions and the ballistic transport of photoexcited electrons in the metal. This low value of internal photoemission allows us to achieve a spectral rejection ratio betwee…
How does graphene enhance the photoelectric conversion efficiency of dye sensitized solar cells? An insight from a theoretical perspective
2019
The main goal of this work is to clearly answer the question from a theoretical perspective: how does graphene enhance the photoelectric conversion efficiency in the semiconducting layer of a dye sensitized solar cell? Several arrangements of the graphene layer between the dye molecule and the TiO2 (101) surface are carefully studied and discussed. The dynamic interfacial electron propagations are simulated with consideration of the underlying nuclear motion effect. Theoretical investigation shows that graphene can speed up the electron injection from the dye molecules to the semiconductor layer, only when the graphene sheet is bonded to the TiO2 surface via C–Ti bonds. The excited electron…
Miniature magnetic devices for laser-based, table-top free-electron lasers
2007
Truly table-top sized radiation sources based on compact laser-plasma accelerators require compact and strong focusing devices and efficient short-period undulators. Complementing our recent theoretical work on the feasibility of a table-top FEL, we here present the design and successful experimental characterizations of a 5 mm period length undulator and miniature quadrupole magnets with field gradients of the order of $500\text{ }\text{ }\mathrm{T}/\mathrm{m}$.
Frequency comb generation in whispering gallery mode silica microsphere resonators
2021
Optical frequency combs (OFC) using different kinds of whispering-gallery-mode (WGM) microresonators have already shown different applications and especially their applications in fiber optical communication systems as replacements of laser-arrays. For this application the free spectral range (FSR) of 200 GHz or less is desirable. Besides the fabrication material for microspheres, the resonator radius can be modified to change the FSR. In this paper use of silica microspheres for OFC represents an inexpensive alternative over the other microcombs: microring, microdisk, and microtoroid. We experimentally present a microsphere fabrication process from a different kind of silica (SiO2) fibers …
Thermally Tunable Surface Acoustic Wave Cavities
2020
We experimentally demonstrate the dynamical tuning of the acoustic field in a surface acoustic wave (SAW) cavity defined by a periodic arrangement of metal stripes on LiNbO3 substrate. Applying a dc voltage to the ends of the metal grid results in a temperature rise due to resistive heating that changes the frequency response of the device up to 0.3%, which can be used to control the acoustic transmission through the structure. The timescale of the switching is demonstrated to be of about 200 ms. In addition, we have also performed finite-element simulations of the transmission spectrum of a model system, which exhibits a temperature dependence consistent with the experimental data. The adv…
Interface engineering in efficient vacuum deposited perovskite solar cells
2016
Abstract We studied the effect of the charge transport layers in p-i-n perovskite solar cells using vacuum deposited methylammonium lead iodide thin-film absorbers. While solution-processed perovskite films are frequently deposited directly on PEDOT:PSS leading to good solar cell performances, in some cases even to very good Voc values, we show that in devices employing vacuum deposited MAPbI3 perovskites, the removal of the polyTPD electron blocker substantially reduces the photovoltaic behavior. This is indicative of rather different charge transport properties in the vacuum deposited MAPbI3 perovskites compared to those prepared from solution. On the other hand, we investigated the use o…