David Gachet
Aix-Marseille University
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Publication
Featured researches published by David Gachet.
Nano Letters | 2014
Endre Horváth; Massimo Spina; Zsolt Szekrényes; Katalin Kamarás; R. Gaal; David Gachet; László Forró
We report the synthesis of Methylammonium Lead Iodide (CH(3)NH(3)PbI(3)) nanowires by a low temperature solution processed crystallization using a simple slip-coating method. The anisotropic particle shape exhibits advantages over nanoparticles in terms of charge transport under illumination. These results provide a basis for solvent-mediated tailoring of structural properties like the crystallite size and orientation in trihalide perovskite thin films, which, once implemented into a device, may ultimately result in an enhanced charge carrier extraction.
Optics Express | 2008
Davy Gérard; Jérôme Wenger; Alexis Devilez; David Gachet; Brian Stout; Nicolas Bonod; Evgeny Popov; Hervé Rigneault
Latex microspheres are used as a simple and low-cost means to achieve three axis electromagnetic confinement below the standard diffraction limit. We demonstrate their use to enhance the fluorescence fluctuation detection of single molecules. Compared to confocal microscopy with high numerical aperture, we monitor a detection volume reduction of one order of magnitude below the diffraction limit together with a 5-fold gain in the fluorescence rate per molecule. This offers new opportunities for a broad range of applications in biophotonics, plasmonics, optical data storage and ultramicroscopy.
Nano Letters | 2010
David Gachet; Assaf Avidan; Iddo Pinkas; Dan Oron
We experimentally investigate carrier multiplication (CM) in type II CdTe/CdSe quantum dot (QD) heterostructures by the means of a simple and robust subnanosecond transient photoluminescence spectroscopy setup. Experimental conditions were set to minimize the blurring of the CM signature by extraneous effects. The extracted photon energy threshold for CM is consistent with previous studies in CdSe and CdTe QDs (around 2.65 times the type II energy band gap) and we can infer an upper bound to CM yield. This study indicates that, while CM is probably present in type II QD heterostructures below the CM threshold for each constituent separately, it exhibits only a modest yield.
Applied Optics | 2006
Nadia Djaker; David Gachet; Nicolas Sandeau; Pierre-François Lenne; Hervé Rigneault
Coherent anti-Stokes Raman scattering (CARS) microscopy with high sensitivity and high three- dimensional resolution has been developed for the vibrational imaging of chemical species. Due to the coherent nature of the CARS emission, it has been reported that the detection of epi-CARS and forward-CARS (F-CARS) signals depends on the size and shape of the sample. We investigate theoretically and experimentally the effects on the CARS signal of refractive index mismatches between the sample and its surroundings. Backward-CARS and F-CARS signals are measured for different polystyrene bead diameters embedded in different refractive index solvents. We show that index mismatches result in a backward-reflected F-CARS signal that generally dominates the experimentally backward-detected signal. Simulations based on geometrical and wave optics comparing forward- and backward-detected signals for polystyrene beads embedded in different index solvents confirm our findings. Furthermore, we demonstrate that the maxima of forward- and backward-detected signals are generated at different positions along the optical axis in the sample if refractive index mismatches are present between the sample and its surroundings.
ACS Nano | 2010
Heykel Aouani; Stella Itzhakov; David Gachet; E. Devaux; Thomas W. Ebbesen; Hervé Rigneault; Dan Oron; Jérôme Wenger
Optical antennas are essential devices to interface light to nanoscale volumes and locally enhance the electromagnetic intensity. Various experimental methods can be used to quantify the antenna amplification on the emission process, yet characterizing the antenna amplification at the excitation frequency solely is a challenging task. Such experimental characterization is highly needed to fully understand and optimize the antenna response. Here, we describe a novel experimental tool to directly measure the antenna amplification on the excitation field independently of the emission process. We monitor the transient emission dynamics of colloidal quantum dots and show that the ratio of doubly to singly excited state photoluminescence decay amplitudes is an accurate tool to quantify the local excitation intensity amplification. This effect is demonstrated on optical antennas made of polystyrene microspheres and gold nanoapertures, and supported by numerical computations. The increased doubly excited state formation on nanoantennas realizes a new demonstration of enhanced light-matter interaction at the nanoscale.
Beilstein Journal of Organic Chemistry | 2013
Laura Bekere; David Gachet; Vladimir Lokshin; W. Marine; Vladimir Khodorkovsky
Summary Of a series of 4-substituted 1,8-naphthalimides, fluorescent 4-(6-piperidinyl-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzoic acid (4) was found to be a sensitive molecular probe for ZnO nanoparticles. We investigated in detail one- and two-photon absorption properties of this fluorophore. In nonpolar solvents, the acid 4 absorbs at about 400 nm and fluoresces at 500 nm with a fluorescence lifetime of about 7 ns, similar to the ester 6 and typical of the lifetimes of other derivatives of this type. Although the anionic form of this acid is not fluorescent, partial ionization of 4 in polar solvents, such as ethanol and acetonitrile, is not only accompanied by the expected decrease in the fluorescence quantum yield, but also gives rise to bathochromic shifts of both absorption and fluorescence and dual fluorescence with lifetimes of 0.2–0.3 ns and 6 ns ascribed to the formation of anionic complexes. The interaction with the ZnO surface brings about further considerable changes in the fluorescence patterns.
Journal of the European Optical Society: Rapid Publications | 2006
David Gachet; Nicolas Sandeau; Hervé Rigneault
We propose a full-vectorial numerical study of far-field radiation patterns in coherent anti-Stokes Raman scattering(CARS) microscopy. We emphasis the particular role of the Raman depolarization ratio of the observed medium and show how it modifies the radiation pattern of thin objects.
Biomedical optics | 2006
David Gachet; Nicolas Sandeau; Hervé Rigneault
Far field radiation pattern under tight focusing condition is investigated in Coherent Anti-stokes Raman Scattering (CARS) microscopy both in the forward (F-CARS) and backward (E-CARS) directions. While we assume no refraction index mismatch between the sample and the environing medium, our rigorous numerical electromagnetic computation takes into account the exact polarizations of the excitation laser beams and of the induced nonlinear dipoles. F-CARS and E-CARS radiation patterns, as well as their divergence, are studied as a function of the size of the sample object and compared to the excitation beams.
Archive | 2012
Hervé Rigneault; David Gachet
We present here the various methodologies that permit to achieve high speed Raman imaging through stimulated processes. Both coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) are considered. Because CARS imaging is affected by a non-resonant contribution, we concentrate here on methods that can remove this non-resonant background in CARS microscopy. We next present the principles of SRS imaging and its implementation in microscopy. We finally present a hyperspectral microscopy setup that is able to perform CARS and SRS together with other nonlinear optical contrasts [second harmonic generation (SHG), two-photon excited fluorescence (TPEF)] and show some results in the field of skin imaging.
Optics Letters | 2009
David Gachet; Franck Billard; Hervé Rigneault
We study tight focus coherent anti-Stokes Raman scattering (CARS) emission in a microcavity where the active medium is squeezed between two independent planar mirrors. We show strong modifications in the CARS forward and backward far-field radiation patterns. For low-order cavities, we demonstrate that most of the emitted power can be concentrated into a direction perpendicular to the mirrors.