The Lorenz model for single-mode homogeneously broadened laser: analytical determination of the unpredictible zone

We have applied harmonic expansion to derive an analytical solution for the Lorenz-Haken equations. This method is used to describe the regular and periodic self-pulsing regime of the single mode homogeneously broadened laser. These periodic solutions emerge when the ratio of the population decay rates is smaller than 0.11. We have also demonstrated the tendency of the Lorenz-Haken dissipative system to behave periodic for a characteristic pumping rate "2CP" [4], close to the second laser threshold "2C2th" (threshold of instability). When the pumping parameter "2C" increases, the laser undergoes a period-doubling sequence. This cascade of period doubling leads towards chaos. We study this type of solutions and indicate the zone of the control parameters for which the system undergoes irregular pulsing solutions. We had previously applied this analytical procedure to derive the amplitude of the first, third and the fifth order harmonics for the laser-field expansion [4, 14]. In this work, we extend this method in the aim of obtaining the higher harmonics. We show that this iterative method is indeed limited to the fifth order, and that above, the obtained analytical solution diverges from the numerical direct resolution of the equations.Comment: 20 pages, 4 figures, 1 anne

Kindling molecules: a new way to ‘break’ the Abbe limit

International audienceFluorescence microscopy is a key tool for biological investigations. However, compared to other techniques like electron microscopy, the achievable resolution is still limited. Tremendous efforts have been devoted to improve the resolution of far-field optical microscopy. Several techniques do exist; however their adoption by biologists has been slowed by several technical limitations. We propose a new method based on a recently discovered family of optically switchable fluorescent molecules. Kindling proteins open the way to very high resolution in far-field fluorescence 3-D microscopy with relatively simple techniques

Polarized confocal theta microscopy

International audienceWe propose a comprehensive treatment of theta microscopy based on dipole emission, which better describes fluorescence emission than the isotropic emission model, as fluorescence emission is often polarized. Formulas describing the point spread function for polarized confocal fluorescence theta microscopy are given. Examples are given and some advantages of polarized theta fluorescence microscopy are presented

Isotropic-Resolution Tomographic Diffractive Microscopy

International audienceMicroscopy techniques based on recording of the optical field diffracted by the specimen, in amplitude and phase, like Digital Holographic Microscopy (DHM) have been a growing research topic in recent years. Tomographic acquisitions are possible if one is able to record information, while controlling variations of the specimen illumination. Classical approaches consider either illumination variation, simple to implement, but suffering fro the classical "missing cone" problem, or sample rotation, delivering images with quasi-isotropic, but lower resolution. We have developed an original-, combined tomographic diffractive microscope setup, making use of specimen rotation as well as illumination rotation, which is able to deliver images with an almost isotropic resolution better than 200 nm

Mécanismes d'usure de revêtements de nitrure de titane et d'aluminium en microtribologie

Le comportement à l’usure de films minces de Ti1-xAlxN (0 ≤ x ≤ 1) déposés par PVD est caractérisé et analysé en fonction de la micro et nano-structure des couches. La structure de ces films est à l’origine de leurs propriétés fonctionnelles. Les directions de croissance des films nanostructurés ont été mesurées par diffraction des rayons X. Les modes d’endommagement des films ont été obtenus par des essais de microtribologie à température ambiante contre une bille d’alumine pour pallier l’usure du pion, à faible chargement et faible vitesse de glissement, pour éviter la formation de couches d’oxyde en surface. Pour comprendre les mécanismes d’usure engendrés par le frottement de la bille, plusieurs essais ont été mis en œuvre : détermination de la ténacité par des essais de rayure, observation de la trace par microscopie électronique à balayage et mesure du volume d’usure après plusieurs allers-retours par profilométrie interférométrique par holographie. Lorsque les débris d’usure restent piégés dans le sillon, leur quantité, directement liée à la résistance à l’initiation de fissures du revêtement, et leur nature, ductiles ou fragiles, ont une grande influence sur l’endommagement final. Les films à forte teneur en aluminium texturés selon la direction [002] du réseau hexagonal, présentent un comportement fragile. Lorsque la teneur en aluminium augmente, le nombre de cycles au bout duquel le coefficient de frottement subit un accroissement considérable diminue. Le nombre de cycles à partir duquel le coefficient de frottement augmente considérablement diminue lorsque la concentration en aluminium augmente. Les films riches en titane dont la direction principale de croissance est [200] du réseau cubique, présentent un meilleur comportement à l’usure. Pour ces films ductiles, l’existence de domaines orientés suivant la direction [111] semble jouer un rôle important sur la ténacité. En effet, la quantité de débris générés est liée à une plus ou moins grande proportion de domaines cristallisant dans cette direction

Validation of image processing tools for 3-D fluorescence microscopy

International audience3-D optical fluorescent microscopy becomes nowadays an efficient tool for volumic investigation of living biological samples. Using optical sectioning technique, a stack of 2-D images is obtained. However, due to the nature of the system optical transfer function and non-optimal experimental conditions, acquired raw data usually suffer from some distortions. In order to carry out biological analysis, raw data have to be restored by deconvolution. The system identification by the point-spread function is useful to obtain the knowledge of the actual system and experimental parameters, which is necessary to restore raw data. It is furthermore helpful to precise the experimental protocol. In order to facilitate the use of image processing techniques, a multi-platform-compatible software package called VIEW3D has been developed. It integrates a set of tools for the analysis of fluorescence images from 3-D wide-field or confocal microscopy. A number of regularisation parameters for data restoration are determined automatically. Common geometrical measurements and morphological descriptors of fluorescent sites are also implemented to facilitate the characterisation of biological samples. An example of this method concerning cytogenetics is presented