Transmission d'image assistée par le bruit en imagerie cohérente et incohérente

La possibilité d'une influence bénéfique du bruit est étudiée sur les performances d'un système imageur non linéaire à seuil, en présence de bruit multiplicatif de type speckie ou de bruit additif comme le bruit thermique, tels qu'on les rencontre en imagerie cohérente et incohérente. Nous montrons, pour ces deux types de bruit, l'existence de régimes de fonctionnement où leur action peut améliorer la qualité de l'image transmise par le système imageur. Des expressions analytiques exactes de la performance optimale, ainsi que du niveau de bruit correspondant à injecter, sont obtenues. Ces expressions permettent de mieux comprendre les effets de bruit utile spécifiques à l'imagerie

Tunable circularly polarized lasing emission in distributed feedback dye lasers

A tunable circularly polarized distributed feedback (DFB) laser based on reflection grating configuration was realized in a solution of 4- (dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) doped methanol. Chiral photonic DFB structures with tunable photonic bandgap were generated by controlling the state of polarization of the two interfering pump beams. The dual-peak lasing emission spectrum indicates that the periodic chiral DFB grating is affected by a combination of modulations of gain and refractive index

Study of crystalline molecular machines by nonlinear microscopy

Date du colloque : 09/2011International audienc

Photochemical properties of side-chain coumarin polymers

Date du colloque&nbsp;: 12/2008Photosensitive materials attract many attention due to their potential application in optical devices such as optical data storage, optical communication, ...[1]. Coumarines and their analogues are well-known for their reversible photoinduced cyclodimerisation properties, leading to cyclobutane-based dimers (scheme) [2]. This equilibrium can be tuned according to the wavelength which is applied, and the resulting systems are of course dramatically structurally and electronically different. Therefore, the coumarine system offers a unique opportunity for applications in various fields involving conjugated molecular frameworks. In the area of photonics and nonlinear optics one of the great advantages of functionalized materials lies on the photochemical properties of the polymer. In the present work, homo- and copolymers built from the free radical polymerization of methacrylic monomers incorporating a coumarin side-group have been synthesized and structurally characterized. Results of photochemical and optical activities of the corresponding polymers will be presented.</p

Single-Particle Tracking with Scanning Non-Linear Microscopy

This study describes the adaptation of non-linear microscopy for single-particle tracking (SPT), a method commonly used in biology with single-photon fluorescence. Imaging moving objects with non-linear microscopy raises difficulties due to the scanning process of the acquisitions. The interest of the study is based on the balance between all the experimental parameters (objective, resolution, frame rate) which need to be optimized to record long trajectories with the best accuracy and frame rate. To evaluate the performance of the setup for SPT, several basic estimation methods are used and adapted to the new detection process. The covariance-based estimator (CVE) seems to be the best way to evaluate the diffusion coefficient from trajectories using the specific factors of motion blur and localization error

3-(p-nitrophenyl)Coumarin derivatives: Synthesis, linear and nonlinear optical properties

International audienc

Functional Low Molecular Weight Gelators: Towards Spontaneous Second Harmonic Generation

International audienc

High resolution patterning of quadratic non-linear optical properties in doped photopolymer thin films

We demonstrate the patterning of the quadratic non-linear optical (QNLO) properties in a photopolymerizable resin doped with push–pull chromophores. Advantage is taken of the crosslinking process to perform the patterning directly. QNLO gratings with a period of 8.5 μm have been achieved over areas of a few cm2. This spacing is comparable to the typical visible and near infrared coherence lengths in this material and is therefore suitable for the elaboration of quasi-phase matched waveguides. An accurate characterization of the QNLO gratings has been performed using a high spatial resolution second harmonic generation microscope with a femtosecond laser source