Search results for "Lasers"
showing 10 items of 316 documents
Refractive micro-optical elements for surface plasmons: from classical to gradient index optics.
2010
Controlling the propagation of surface plasmons along a metal-dielectric interface is a key feature for the development of surface plasmon based circuits. We have designed various two-dimensional refractive dielectric optical elements for surface plasmons (SP) and characterized their capacity to route SP, using near- or far-field techniques. We first present basic devices analogous to usual optical components and the associated challenges for SP optics. We then use a metamaterial approach to locally vary the refractive index and fabricate gradient index structures for SP circuitry.
Alterations in membrane and firing properties of layer 2/3 pyramidal neurons following focal laser lesions in rat visual cortex.
2013
Focal cortical injuries are well known to cause changes in function and excitability of the surviving cortical areas but the cellular correlates of these physiological alterations are not fully understood. In the present study we employed a well established ex vivo-in vitro model of focal laser lesions in the rat visual cortex and we studied membrane and firing properties of the surviving layer 2/3 pyramidal neurons. Patch-clamp recordings, performed in the first week post-injury, revealed an increased input resistance, a depolarized spike threshold as well as alterations in the firing pattern of neurons in the cortex ipsilateral to the lesion. Notably, the reported lesion-induced alteratio…
Remote estimation of blood pulse pressure via temporal tracking of reflected secondary speckles pattern
2011
We present a novel technique for remote noncontact blood pulse pressure measurement. It is based on tracking both temporal and amplitude changes of reflected secondary speckle produced in human skin when illuminated by a laser beam. The implemented technique extracts the difference between the systolic and the diastolic blood pressure. Experimental results are presented showing good agreement when compared with conventional measurement methods.
Low level 809-nm diode laser-induced in vitro stimulation of the proliferation of human gingival fibroblasts
2002
Background and Objective The authors investigated the effects of low level laser irradiation on the proliferation rate of human gingival fibroblasts (HGF) in vitro. Study Design/Materials and Methods HGF were obtained from gingival connective tissue explants and cultured under standard conditions. 110 cell cultures in their logarithmic growth phase were spread on 96-well tissue culture plates and were irradiated at energy fluences of 1.96–7.84 J/cm2. Another 110 cultures served as control. An 809-nm semiconductor laser operated at a power output of 10 mW in the cw-mode was used. The time of exposure varied between 75 and 300 seconds. Laser treatment was performed alternatively once, twice, …
Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopy.
2015
International audience; We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. Data at the Fe K-edge reveal that the photoinduced structural changes at the heme occur in two steps, with a faster (∼70 fs) relaxation preceding a slower (∼400 fs) one. We tentatively attribute the first relaxation to a structural rearrangement induced by photolysis involving essentially only the heme chromophore and the second relaxation to a residual Fe motion out of the heme plane that is coupled to the displacement of myoglobin F-helix
Current status of AlInN layers lattice-matched to GaN for photonics and electronics
2007
We report on the current properties of Al1-x InxN (x approximate to 0.18) layers lattice- matched ( LM) to GaN and their specific use to realize nearly strain- free structures for photonic and electronic applications. Following a literature survey of the general properties of AlInN layers, structural and optical properties of thin state- of- the- art AlInN layers LM to GaN are described showing that despite improved structural properties these layers are still characterized by a typical background donor concentration of ( 1 - 5) x 10(18) cm(-3) and a large Stokes shift (similar to 800 meV) between luminescence and absorption edge. The use of these AlInN layers LM to GaN is then exemplified …
Blue lasing at room temperature in high quality factor GaN/AlInN microdisks with InGaN quantum wells
2007
The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of InGaN/GaN quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found (Q>4000). Laser action at similar to 420 nm is achieved under pulsed excitation at room temperature for a peak power density of 400 kW/cm(2). The lasing emission linewidth is down to 0.033 nm.
A laser-based system for a fast and accurate measurement of gain and linearity of photomultipliers
2018
This paper describes a method for the measurement of gain and linearity of photomultipliers (PMTs). Gain and linearity are two fundamental parameters to use properly a PMT in several physics experiments. In the developed system light is laser generated and adressed to the PMT through a set of optical fibers. The data acquisition system consists in a commercial 16 channel digitizer coupled to a custom front-end board. With the chosen digitizer the system is scalable to test up to 16 PMTs, with the aid of a light distribution system and a multi-channel version of the front-end board. Data analysis is performed by a custom acquisition software. A 1.5» Hamamatsu PMT is used to validate the syst…
Nanoparticle One-Dimensional Photonic-Crystal Dye Laser
2009
The stimulated emission from an organic dye adsorbed within the void network of a NP 1D (photonic crystals) PC, was studied. The nanoparticle one-dimensional photonic crystals (NP 1DPCs) were assembled by polyelectrolyte-assisted layer-by-layer deposition with subsequent calcination of the films to remove the polymer components. Each layer was prepared by spin-coating a block-copolymer-templated titania- or silica-based sol solution followed by a calcination step. To maximize the photonic-crystal effect, PCs consisting of eleven bilayers, compared to the four-bilayer NP 1D PCs, were fabricated with good structural and optical quality over 2 cm ×2 cm areas. The effective refractive index of …
Subpicosecond transient signal spectroscopy of Prodan in dimethylformamide solution.
2008
We report a pump-probe experiment revealing the temporal evolution of subpicosecond evolution of Prodan's excited-state absorption in dimethylformamide. Also, we present calculation of the first spectral moment of this spectral band and estimation of different relaxation components on the subpicosecond time scale.