Interferometrie a grande difference de marche en lumiere blanche

A new method for measuring the visibility of the spectral modulation in an interferometry experiment where the path difference is made much larger than the coherence length has been described recently. A measure of the visibility of the spectral modulation using a white light source over a path difference up to 10.7 meters is reported.     

Determination des lignes de niveau par double photographie en lumiere coherente

Two images of a rough curved object, illuminated by a coherent parallel beam are recorded on the same photographic plate. The incident beam is slightly tilted between the two exposures. In a suitable filtering set-up we observe the depth contours of the object (parallel to the photographic plate); the experimental limitations are discussed.     

Transmission optique,en lumiere polarisse,de couches tres minces de potassium,sous incidence oblique

The transmission factors of potassium thin films have been determined for incidence angles of 0°, 45°, 70°, the electric field E being either parallel or perpendicular to the incidence plane. These factors present important differences according to the polarization. Evidence has been found for the existence of two anomalous absorption bands. These bands can be connected with the existence of two plasma frequencies, which are associated with an electric field component parallel or perpendicular to the thin film.     

Transmission optique,en lumiere polarisee,de couches tres minces de sodium,sous incidence oblique

The transmission factors of sodium in thin films have been determined for incidence angles of 0°, 45°, 70°; the electric field E being either parallel or perpendicular to the incidence plane. These factors present important differences according to polarization.     

Enregistrement et selection de mode d'une fibre optique par spectroscopie optique cohérente

Résumé En utilisant des techniques de spectroscopie optique cohérente, on réalise, avec une résolution subpicoseconde, une sélection temporelle des différentes modes qui se propagent dans une fibre optique multimodale. La structure spatiale, en intensité, des modes excités est visualisée par filtrage optique d'un hologramme de Fourier. Une démonstration expérimentale est présentée dans le cas élémentaire d'une fibre bimodale.

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Using coherent optical spectroscopic techniques, we perform a temporal selection of the different modes propagating in a multimode optical fibre, with subpicosecond resolution. The intensity patterns of the excited modes are visualized by optical filtering of a Fourier hologram. An experimental demonstration is presented in the elementary case of a bimodal fibre.

     

Les effets causes par les dimensions de la source dans les systemes optiques eclaires en lumiere spatialement incoherente

It has been shown recently that in order for an incoherent optical system to be linear and space invariant, the image of the source at the filter plane must be larger than the filter aperture. We show in this paper that the source image must be larger than the filter by an amount equal to twice the highest spatial frequency of the object, the frequency being measured in the filter plane.     

Extraction d'invariants morphologiques d'une information par correlation optique et filtrage spatial

The set of characters on a page of text may be described as a two-dimensional random distribution of morphological constants (linguistic data and spread function of the writer) to which a gaussian noise is superimposed. Processing the whole page by using optical correlation and spatial filtering techniques allow one to extract these constants, thus supplying a recognition test of the writer. The general principles are explained, and the distinction of two type writer founts is experimentally verified.     

Mesure en temps réel des variations du temps de transit dans un câble optique multifibre

Measurements in real time of the delay time of the signal in optical fibres in a cable have been performed both by the pulse method and a phase method. The experimental arrangement and principle of the methods are presented. The evolution of the results against temperature is discussed.

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Cette étude a été financée par un contrat de l'Institut National d'Astronomie et de Géophysique (I.N.A.G.).     

Propagation soliton et auto-confinement de faisceaux laser par non linearité optique de kerr

An experimental demonstration is presented of the stable monomode self-trapping of laser beams with adequate shape and power when they are propagating through homogeneous transparent dielectrics whose refractive index exhibits fluctuations proportional to the local intensity. The field evolution in such material is governed by a nonlinear scalar wave equation, that possesses stable solutions called solitons. Those solutions correspond to the exact balance of the natural diffraction divergence of the beam by the convergence of the self-induced refractive index gradient.     

Mise en oeuvre et optimisation d'un modulateur de retard optique

An optical phase modulator using a polarization interferometer described by Jamin is studied. The best theoretical and experimental modulation amplitude of the phase is searched for, to obtain the best accuracy conditions to measure the optical path difference between the two beams of the interferometer. Effects of finite values of numerical aperture and effective wavelength range are also studied.     

Obtention des bandes de cameron par photo excitation de co en matrices d'argon de krypton et de xenon

CO trapped in solid matrices of argon, krypton and xenon has been excited by 10 eV photons. Cameron bands v′=0, v″=0,1,2,3,4 are observed during the irradiation. If red shifts are observed in argon and krypton matrices, the transition in xenon shows no differences with gas phase data.     

Transmission d'images et d'hologrammes par une nappe de fibres optiques au moyen d'un codage chromatique

A new method of addition of 2-D complex optical signals is proposed. The addition is performed by suitably matched spatial filtering. For that purpose the effect of compacting of periodic objects images is employed.     

Etude de l'absorption optique du vanadium en couches minces interpretation par la theorie des bandes d'energie

Optical absorption of vanadium thin films has been determinated from 0.32 to 5.5 eV from reflectance and transmittance data. The films have been deposited in ultra high vacuum and the measurements have been realised in situ. Between 1 to 5.5 eV, we note a large absorption band which is independant of the photons angle of incidence and polarisation; with an important maximum and a shoulder respectively at 3.1 and 2 eV. We explain this absorption band by direct interband transitions deduced from theorical bands calculated by Yasui et al. From 0.32 to 1 eV, the observed absorption is principally due to intraband transitions.     

Excitation par un rayonnement optique d'ondes de plasma de surface dans des structures multicouches: Coefficient de réflexion et répartition locale de l'énergie

The general dispersion relation of surface plasma oscillations (SPO) excited in a multilayered medium made of n thin films having a complex permittivity is given, using a formalism well adapted to numerical calculations. The electromagnetic (EM) energy density repartition in the films — and along the interface — as well as the reflection coefficient R of the system illuminated by a plane p-polarized wave under variable incidence are then calculated. Practical examples concerning typical metal-insulator (MI) or metal-insulator-metal (MIM) devices are then given, showing the exact localization of the excited SPO corresponding to a minimum of R and the resulting enhancement of the energy density.     

Etude en fonction du temps de l'oxydation des magnetites substituees a l'aluminium et au chrome au moyen de la conductivite electrique

The oxidation of substituted magnetites (Fe²⁺Fe_2?x³⁺M_x³⁺O₄^2?(O < x < 2) into the lacunar phase γ(Fe_1?z³⁺M_z³⁺)O₃^{2 ?} (x = 3z) was followed over time by electrical conductivity over the temperature r Curves σ = f(t) are different according to whether we deal with an n or p-type spinel. However, for intermediate substitution rates (1,1 < x < 1,8), n-type ferrichromites are oxidized after an initial period in the same way as p-type semi-conductors.For the initial period, the chemisorption kinetics of oxygen upon these n-type samples, reduced under vacuum, was found to follow Elovich's law with an activation energy depending on the degree of coverage.     

Un nouveau theoreme d'echantillonnage pour le degre de coherence complexe en vue de la reconstitution d'une source lumineuse isotrope

We present some results obtained by using the standard technique of light scattering on so-called “microemulsions”. From the data of single-photon counting of light scattered from 0° to 90° the particle scattering factor P(θ) is obtained. Fitting with the theoretical curves gained for various kinds of particles enables us to deduce in a rather direct and simple way the shape and the size of particles.     

Mesure de la conductivite electrique totale du protoxyde de cobalt en fonction de sa composition definie par des electrodes d'alliage cobalt-platine,entre 1000 et 1400 K

The total electrical conductivity of cobaltous oxide has been measured from 1000 to 1400 K as a function of its composition, especially in the range of low oxygen pressures up to the limit of equilibrium with cobalt. These measurements have been carried out with monocrystalline samples of oxide placed between cobalt-platinum alloy electrodes; oxide composition is fixed by the activity of cobalt in the alloy which is also the activity of cobalt in oxide. Results are given by isotherm curves of the logarithm of conductivity versus the logarithm of oxygen pressure. The slope of these isotherms shows a regular variation between $\text{1}\text{4}$ and less than $\text{1}\text{6}$; this fact can only be explained by the successive effects of the formation of vacancies V″_Co, V′_Co and of intrinsic conductivity by electrons and free holes.     

Une ‘méthode des franges’ en temps réel et ses applications industrielles: déformations,vibrations, courbes de niveau

A new technique using a point source fringe projection and a real time video processing combined with electronic filtering is applied to vibration measurements, deformation and relief mapping. Projection system, gratings, real time video and electronic techniques are described.Experimental results and interpretation are presented.Qualitative and quantitative industrial applications are discussed.     

Les pyrochlores ferroelectriques derives de Cd2Nb2O6S: Mise en évidence des transitions de phase par des techniques d'optique non linéaire

The ferroelectric pyrochlore compound Cd₂Nb₂O₆S and solid solution Cd₂Nb₂O_7?xS_x have been studied by second optical harmonic generation. The excitation source was a YAG: Nd³⁺ laser emitting at λ = 1.06 μm. The intensity variation of second harmonic as a function of temperature was investigated. A strong signal appears in the two ferroelectric phases. The transition temperatures are easily observed; dielectric and calorimetric results are confirmed.