Correction des effets de l''image jumelle et du terme quadratique en holographie de Gabor

An iterative method to suitably solve the problem of the twin image and quadratic term in Gabor's holography is presented. This method gives useful information regarding the uniqueness of the solution and the sensitivity of the results to all types of errors. In particular, it appears that the hologram can be obtained in optical conditions intermediate between the Fraunhofer and the Fresnel conditions. This is of special interest in the case of Zernike-Gabor objects because of the signal-to-noise ratio. This technique seems to be well suited to the problems involved in electron microscopy. The applications concern the analysis at high resolution of structures in biology and in physics of condensed matter.     

Calculs numeriques de facteurs de Franck-Condon et effets isotopiques: Effet de la rotation au cours de predissociations

On montre que le facteur de Franck-Condon intervenant dans la largeur de raie due à la prédissociation, varie d'autant plus vite avec J (nombre quantique de rotation) que l'intersection des courbes de potentiel est franche (cas ⁺ de la classification de Mulliken). Cette variation est bien reproduite dans les cas ⁺ par la formule donnée par Child en 1970 Γ = Γ₀ cos² η, où η est une intégrale de phase.     

Emploi quantitatif de la spectroscopie Auger; Étalonnage de la méthode

A calibration is presented for the measurement, by Auger electron spectroscopy, of sulphur adsorbed on nickel. The Auger emission from the metal is used as a reference. The use of radioactive sulphur permits a direct measurement of the quantity of adsorbed sulphur.     

Fentes consommables et cibles incrustees en spectroscopie X par laser

Consumable slits close to a laser produced plasma improve the signal to noise ratio of spatially resolved X-ray spectra. Also, a new technique allows a variety of materials to be used as inlaid tracers for spot spectroscopy.     

Étude par spectroscopie auger,diffraction d'électrons lents et rapides des premiers stades de la sulfuration de la face (100) de NiO par H2S

A structural study of the different stages during NiO(100) sulphurization by H₂S was carried out by RHEED, LEED and AES. On exposure to H₂S (PH₂S < 10^?5 Torr) The “clean” surface, obtained by UHV cleavage, was found to react with H₂S to produce islands of Ni(100) covered with an ordered c(2 × 2) S structure up to 300°C. Growth of Ni₃S₂ islands occurs on increasing the temperature and the exposure to H₂S.     

Contribution a l'etude de l'effet de charge sur echantillon isolant en spectroscopie de photoelectrons (XPS)

The accurate measurement of sample current for several non-conducting materials studied by XPS has proved that this effect is negligible and does not contribute to the surface potential determination. The influence of parameters of the sample (surface state, geometry, emission yield), those of the spectrometer (X-ray intensity, retarding potential), and the consequence of the use of a flood gun have been studied on simulated insulating samples starting from electrical characteristics and an exact value of the surface potential. Mechanisms are proposed to explain the different effects observed. The results show that electrical compensation of charge effect is difficult and that the energy scale linearity is affected on a retarding field spectrometer.     

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.     

Étude par la diffraction des électrons lents et la spectroscopie auger de l'adsorption du soufre sur le platine

The adsorption of sulphur on the (111), (100) and (110) faces of platinum has been studied by LEED and Auger spectroscopy. By the combined use of radioactive S³⁵ the contents of the surface unit meshes were determined “in situ” for each state of adsorption. On the (111) face one observes a preliminary adsorption with localization of sulphur atoms at sites of maximum coordination of the metal. At higher pressures and temperatures, S-S distance contracts and a compact hexagonal arrangement, with sulphur atoms outside sites, is obtained. The thermal stability of the various structures was studied as a function of sulphur coverage. During adsorption on the (100) and (110) faces, two steps may be distinguished: the first one seems to correspond to an adsorption in sites, the second corresponds to the formation of a two-dimensional compound whose square mesh is slightly different on the two faces.     

Surfaces de Fermi,profil Compton et effets a N-corps

Nous montrons théoriquement qu'il est possible de déterminer les surfaces de Fermi à partir de profils Compton de métaux même lorsque l'on tient compte des effets à N-corps dans leur totalité.     

Correlations entre la conductivite ionique et la concentration en ions alcalins dans les borates de lithium vitreux

The electrical transport properties of the B₂O₃ - xLi₂O glasses have been investigated. An electrochemical approach allows to give an interpretation of the conductivity based on the carrier concentration in relation with Li₂O content. The mobility of the Li⁺ ions does not seem to depend on the composition.     

E´tude par la diffraction dese´lectrons lents et la spectroscopie auger de l'adsorption du soufre sur l'or

A study has been made of the adsorption of sulphur on the (111), (100) and (110) faces of gold using LEED and AUGER spectroscopy combined with a radioactive tracer technique employing ³⁵S. The content of the surface unit mesh can thus be determined. A preliminary adsorption state with localization of sulphur atoms at sites of maximum coordination of the metal is observed. This state is transformed by reconstruction into a surface compound, or adsorbed two-dimensional sulphide. The results are compared with previous results from HEED and experiments of reversible chemisorption. On the (110) face the equilibrium between different adsorbed phases of sulphur is studied under conditions for which sulphur dissolution or evaporation is negligible. A temperature- coverage diagram is determined which shows the regions where sulphur is present at equilibrium in one or two phases.     

Calcul semi-empirique de la temperature de transition des superconducteurs et de l'effet de la pression sur la transition

A method is developed to take into account the contribution of the Umklapprozesse to the electron-phonon interaction in polyvalent metals. This method is used to compute—from first principles—the high-temperature resistivity of non-transition metals as well as the transition temperature T_c of non-transition superconductors along the lines of , and 's theory of superconductivity (Phys. Rev. 108, 1175 (1957)). The effect of pressure on T_c is also computed and its dependence upon the band structure is stressed.     

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.

     

Sur la restitution du signe de la phase en interferometrie

Phase variations are transformed into intensity variations by means of interferometry. It is then possible to form a visible image of a pure phase object. But then information on the sign of the phase or the direction of surface relief is lost. Principles of a method for extracting only the imaginary part of the complex amplitude of the object, which is an odd function of the phase, are studied. From this it is possible to obtain the sign of the phase.     

Commentaires sur la détermination de la loi de luminance L(P,θ) d'une source semi-conductrice en champ proche

This paper presents a theoretical and experimental study of the application of the near field technique to the measure of radiance of light emitting diodes and laser diodes. We have shown the possibilities and the limitations of this technique.     

Isomorphisme de Duflo et la cohomologie tangentielle

In the present note we show that the Duflo isomorphism can be extended to an isomorphism of associative algebras of tangential cohomologies. This result confirms the Shoikhet’s conjecture.     

Dispersion des indices de refraction du molybdate de plomb (PbMoO4) et de la paratellurite (TeO2)

An infrared goniometer, shortly described has been used for the determinations of the refractive indices of two interesting acousto-optical materials: lead molybdate (PbMoO₄) and paratellurite (TeO₂). The given results complete those previously available which concern only the visible range. Coefficients of Sellmeier equations for the whole transparency range of both materials are also given and discussed.     

Etude de la cinetique de la reaction de polymerisation de resines epoxy et polyester par analyse du comportement dielectrique

In this piece of research, we have chosen to study the dielectric behaviour of different resins while in process of polymerization and determine the dielectric parameters most relevant to the monitoring of the kinetic process taking place; our aim being to design electromagnetic sensors which will enable us to monitor the polymerization process thoroughout.Consequently we have confined ourselves to carrying out radiofrequency measurements by using only a few set frequencies, without attempting to monitor, as many researchers have tried to, the evolution of dielectric relaxation [1, 5].We have studied two types of resins, one of them being epoxy-based and the other polyester-based. We have succeeded in demonstrating that the perception of the real terms of the complex dielectric constant as well as of the evolution of the loss tangent angle, both complementary elements, are essential for a thorough analysis of the kinetic process.Whereas ε is most suitable for the monitoring of the concluding phase of the polymerization, tan δ is more appropriate to the study of the opening stage of the process, while allowing us to define with great accuracy the exothermicity point reached after gel time [6, 7, 8].     

Resonances en limite semiclassique et exposants de Lyapunov

We determine the width of resonance-free domains in the complex plane for the semiclassical Schrödinger operator –h ²+V(x) whenh0, in terms of Lyapunov exponents for the associated classical flow.