A correct-by-construction model for asynchronously communicating systems

The design and verification of distributed software systems is often hindered by their ever-increasing complexity and their asynchronous operational semantics. This article considers choreography specifications for distributed systems to reduce that complexity. We use labelled state-transitions systems as ground model for both choreographies and the corresponding distributed systems. Based on Event-B method, we propose a stepwise correct-by-construction model to build asynchronous distributed systems which a priori realise their choreographies. We rely on a sufficient and necessary realisability condition and we apply several refinement steps w.r.t. that condition to generate the distributed peers. The first refinement returns peer behaviours obtained by synchronous projection. The previously computed system is then refined into its asynchronous version using unbounded FIFO buffers. We prove, thanks to invariant preservation, that a sequence of exchanged messages is preserved at each refinement step. We provide a formalised proof of a realisability algorithm for deterministic choreographies. Besides that, our contribution is twofold: the approach is a priori and the problackposed solution scales up to any number of peers communicating with each other

Reconstruction-free sensitive wavefront sensor based on continuous position sensitive detectors

International audienceWe propose a new device that is able to perform highly sensitive wavefront measurements based on the use of continuous position sensitive detectors and without resorting to any reconstruction process. We demonstrate experimentally its ability to measure small wavefront distortions through the characterization of pump-induced refractive index changes in laser material. In addition, it is shown using computer-generated holograms that this device can detect phase discontinuities as well as improve the quality of sharp phase variations measurements. Results are compared to reference Shack-Hartmann measurements, and dramatic enhancements are obtained

The Advantages and Disadvantages of Using Structured High-Order but Single Laguerre–Gauss <i>LG</i>_<i>p</i>0 Laser Beams

Most laser applications are based on the focusing of a Gaussian laser beam (GLB). When the latter is subject to a phase aberration such as the optical Kerr effect (OKE) or spherical aberration (SA), it is recognised that the focusing performance of the GLB is degraded. In this paper, it is demonstrated that high-order radial Laguerre–Gauss LGp0 beams are more resilient than the GLB when subject to the OKE or SA. This opens up opportunities to replace with advantages the usual GLB with a high-order LGp0 beam for some applications

Caractérisation et modélisation des lasers solides pompés optiquement

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

A generic formal specification of fusion of modalities in a multimodal HCI

International audienc

Utilisation d'éléments optiques diffractifs binaires pour la mise en forme et l'amélioration des performances des lasers solides

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Caractérisation des effets de lentille de population dans les lasers à solide

Les variations de l indice de réfraction d origine électronique, proportionnelles au nombre d ions actifs du matériau laser portés dans leur état excité et à la variation de polarisabilité entre le niveau excité et le niveau fondamental, peuvent avoir un impact considérable sur les propriétés spatio-temporelles des résonateurs laser. Il est ainsi nécessaire de disposer de méthodes sensibles afin de les évaluer. Ce travail de thèse est donc centré autour de la métrologie de ces effets dits de population , afin d être en mesure de mieux appréhender le comportement des lasers à solide voire d être capable d utiliser ces effets pseudo-nonlinéaires pour diverses applications. La première partie de cette thèse consiste donc à quantifier les effets de population dans des cristaux laser dopés Chrome et Ytterbium à l aide de la technique Z-scan. Dans cette optique, nous avons mis en place une expérience résolue en temps afin de nous affranchir des effets thermiques, phénomène inhérent à tout processus de pompage optique. Nous avons par la suite mis au point une technique originale, appelée Baryscan, permettant de mesurer de très faibles variations d indice et d atteindre une sensibilité parmi les plus grande rencontrée à ce jour. Cette technique est basée sur l utilisation d un Position Sensitive Detector (PSD) et les propriétés non-linéaires des cristaux sont déduites de l évolution du barycentre d un faisceau laser pompe-sonde. Nous présentons de plus des résultats concernant la focalisant diffractive de faisceaux laser à l aide d optiques de phase ainsi que des techniques de mise en forme permettant de forcer une cavité laser à osciller sur le mode transverse souhaité.In ion-doped solid-state laser materials, the pump-induced refractive index changes (RIC) have an electronic component, the so-called population lens effect, which can be related to the change in excited state population and to the polarizability difference between the excited and ground states. These population effects have a tremendous influence upon the spatiotemporal characteristics of laser resonators and it is thus a challenging problem to have sensitive techniques for measuring them. Hence, this PhD thesis is focused on the metrology of the RIC for a better understanding of the solid-state lasers behavior and in order to be able to use these effects for various applications.The first part of this manuscript consists in measuring the population effects in Chromium and Ytterbium-doped laser crystals with the Z-scan technique. For doing so, a time-resolved experiment has been designed in order to discriminate between thermal and electronic effects. In a second part, we have developed a new efficient technique, called Baryscan, able to measure very weak RIC and to reach among the highest sensitivity levels to date. This method is based upon the measurement of optical nonlinearities by means of beam centroid displacements with a Position Sensitive Detector. Besides, interesting results about the diffractive focusing of laser beams with a cascade of phase plates are presented and two beam shaping techniques for forcing a laser to oscillate on a high-order mode are detailed.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Q-switch of a continuously pumped CO2 laser with a scanning coupled-cavity Michelson mirror

International audienceWe report on the possibility of Q-switching a continuously pumped CO2 laser using a scanning Michelson interferometer as an end mirror, instead of the habitual well-known strategies. This method, in addition to its simplicity, produces free tail relaxation pulses having duration of about 1.3 µs, which is comparable to what can be obtained when using a saturable absorber. A pulse repetition frequency as high as 90 kHz is obtained

Un cadre formel générique pour la modélisation d'IHM multi-modales (cas de la multi-modalité en entrée)

Nos travaux proposent un cadre méthodologique formel générique permettant la conception formelle d IHM multi-modales et la formalisation de l expression et de la validation de propriétés d utilisabilité associées. Ce cadre s appuie sur un même modèle formel unifié autour des systèmes de transitions. Dans une seconde partie, nous montrons comment les modèles issus du cadre générique sont mis en oeuvre dans des techniques formelles particulières et hétérogènes du point de vue de la sémantique. Deux catégories de techniques sont abordées. La première fondée sur le model-checking avec deux approches, l une à base de variables d'états et de la logique temporelle arborescente CTL avec l outil SMV et l autre à base d'actions et de la logique temporelle linéaire LTL avec l outil Promela/Spin. La seconde catégorie de technique mise en oeuvre est fondée sur la preuve interactive et sur le raffinement. Elle met en oeuvre la méthode B dans sa version événementielle.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Modelling of a Nd:YAG laser Q-switched by a scanning interferometric mirror

International audienceWe have modelled a continuously pumped Nd:YAG actively Q-switched by a variable interferometric mirror made up of a scanning Michelson or Fabry–Pérot mirror. We have characterised the three-mirror laser dynamics by using a bifurcation diagram constructed from the plot of peak power-enhancement factor as a function of mirror speed. One observes different chaotic windows separated by period-doubling bifurcations, and stable periodic regime. It is demonstrated that the best performance of the Q-switched laser is obtained rather for low than for high mirror speed (pulse width of 20 ns, and high peak power up to 400 times greater than the continuous emission)