Showing papers by "Guilhem Gallot published in 2006"
TL;DR: This achromatic wave plate demonstrates a huge frequency bandwidth (upsilonmax/upsilonmin approximately 7), and therefore can be applied to terahertz time domain spectroscopy and polarimetry.
Abstract: Phase retarders usually present a strong frequency dependence. We discuss the design and characterization of a terahertz achromatic quarter-wave plate. This wave plate is made from six birefringent quartz plates precisely designed and stacked together. Phase retardation has been measured over the whole terahertz range by terahertz polarimetry. This achromatic wave plate demonstrates a huge frequency bandwidth (upsilonmax/upsilonmin approximately 7), and therefore can be applied to terahertz time domain spectroscopy and polarimetry.
268 citations
TL;DR: The coupling between the surface plasmons of two overlapping arrays of orthogonally oriented subwavelength elliptical holes has been demonstrated by terahertz time-domain spectroscopy over the $0.3em, 0.1\char21{}1\phantom{\rule{0.
Abstract: The coupling between the surface plasmons of two overlapping arrays of orthogonally oriented subwavelength elliptical holes has been demonstrated by terahertz time-domain spectroscopy over the $0.1\char21{}1\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ range. This enhanced transmission exhibits polarization sensitive frequency shift. Three-dimensional numerical simulations provide precise insight in the energy redistribution of the surface plasmons through the subwavelength holes. A simple theoretical model, demonstrating a strong coupling between the two subarrays, exhibits good agreement with the experimental data.
55 citations
TL;DR: This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses.
Abstract: We demonstrate the direct and noninvasive imaging of functional neurons by ionic contrast terahertz near-field microscopy. This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore, neuronal activity results from both a precise control of transient variations in ionic conductances and a much less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed ionic contrast terahertz microscopy technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by temperature change or neurotoxin poisoning. Water influx as small as 20 fl per μm of axonal length can be measured. This technique should then provide grounds for the development of advanced functional neuroimaging methods based on diffusion anisotropy of water molecules.
49 citations
TL;DR: In this article, an experimental study of the interaction of ultrashort laser pulses with underdense plasmas in the relativistic regime is presented, where the laser pulse is focused to relativistically intensities and its pulse duration is comparable to or shorter than the plasma period.
Abstract: An experimental study of the interaction of ultrashort laser pulses with underdense plasmas in the relativistic regime is presented. A parameter regime of particular interest was found: the so-called bubble regime. In this regime, the laser pulse is focused to relativistic intensities and its pulse duration is comparable to or shorter than the plasma period. A wealth of physical phenomena occurs for such physical parameters. These phenomena have multiple signatures which have been investigated experimentally: (i) the generation of a high quality electron beam (high energy, very collimated, quasimonoenergetic energy distribution); (ii) the laser pulse temporal shortening in nonlinear plasma waves. In addition, experimental results suggest that the electron beam produced in this way has temporal structures shorter than 50fs.
24 citations
TL;DR: ICT microscopy technique associated with full three-dimensional simulation enabling to measure precisely the fiber sizes should provide the grounds to development of advanced in vivo ion flux measurement in mammalian hearts, allowing the prediction of heart attack from change in K+ fluxes.
Abstract: The authors demonstrate the direct, noninvasive and time resolved imaging of functional frog auricular fibers by ionic contrast terahertz (ICT) near field microscopy. This technique provides quantitative, time-dependent measurement of ionic flow during auricular muscle electrical activity, and opens the way of direct noninvasive imaging of cardiac activity under stimulation. ICT microscopy technique was associated with full three-dimensional simulation enabling to measure precisely the fiber sizes. This technique coupled to waveguide technology should provide the grounds to development of advanced in vivo ion flux measurement in mammalian hearts, allowing the prediction of heart attack from change in K+ fluxes.
23 citations
TL;DR: It is demonstrated that in near field imaging, interaction between light and sample can be divided into two main areas: the true near field and the contrast near field domain.
Abstract: We demonstrate that in near field imaging, interaction between light and sample can be divided into two main areas: the true near field and the contrast near field domain. We performed extensive numerical simulations in order to identify the limits of these areas, and to investigate contrast near field imaging in which much easier propagation calculation can be achieved. Finally, we show an application with terahertz axonal imaging.
9 citations
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TL;DR: In this paper, the authors propose an approach to fully understand the nature of surface electrons in plasmonic systems, by experimentally demonstrating that surface plasmons can be modeled as a phase of surface waves.
Abstract: Carrying digital information in traditional copper wires is becoming a major issue in electronic circuits. Optical connections such as fiber optics offers unprecedented transfer capacity, but the mismatch between the optical wavelength and the transistors size drastically reduces the coupling efficiency. By merging the abilities of photonics and electronics, surface plasmon photonics, or 'plasmonics' exhibits strong potential. Here, we propose an original approach to fully understand the nature of surface electrons in plasmonic systems, by experimentally demonstrating that surface plasmons can be modeled as a phase of surface waves. First and second order phase transitions, associated with percolation transitions, have been experimentally observed in the building process of surface plasmons in lattice of subwavelength apertures. Percolation theory provides a unified framework for surface plasmons description.
2 citations
21 May 2006
TL;DR: In this article, the coupling between the surface plasmons of two overlapping arrays of orthogonally oriented subwavelength elliptical holes has been demonstrated by terahertz spectroscopy.
Abstract: The coupling between the surface plasmons of two overlapping arrays of orthogonally oriented subwavelength elliptical holes has been demonstrated by terahertz spectroscopy. Experimental data are compared to a simple theoretical model and numerical simulations.