We show theoretically and experimentally that the wavelength tunability of an Er3+–doped fiber laser is improved by using a twofold filter combining a Mach-Zehnder interferometer and a polarimetric filter. This new filter allows us to tune continuously the wavelength from 1.53 to 1.56 µm without the discontinuity associated to the narrow transmission bands of a Mach-Zehnder tuning filter.

For some years, Cunat [1] has developed a formalism based on the thermodynamics of irreversible processes in order to describe the behaviour of continuous media which are not in the equilibrium state. This thermodynamics of relaxation has led to a very general modeling called “Distribution of Non-Linear Relaxations” (DNLR) modeling. This theoretical approach is currently applied in solid mechanics for various ways and sequences of loading.In this paper, the application to primary and secondary unidirectional creep is presented. Only five parameters whose physical meaning is known are necessary. We analyze the role of each of them and indicate a process of identification from experimental data.

In order to allow non-destructive characterizations by acoustic microscopy, the materials presenting in their properties a gradient perpendicular to the surface are modelled. The method consists in regarding the material as built of a succession of homogeneous layers numerous enough for the acoustic parameters to varyquasi-continuously. The gradient in Young modulus existing in the material is relatedto a gradient in acoustic properties measurable by acoustic microscopy. The role ofthe shape of the gradient profile is taken into account in the study of theconvergence of the velocity of the surface mode V S. The dispersion of thevelocity V Sversusd/λ (d is the depth of the gradient areaand λ is the wavelength) is studied as a function of the gradient profile. Theshape of the curves shows that the best sensitivity to the profile is obtained ford/λ≈1.

Scanning electron microscopy as well as analytical transmission electron microscopy techniques such as high resolution, electron diffraction, energy dispersive X-ray spectrometry (EDX), parallel electron energy loss spectroscopy (PEELS) and elemental mapping via a Gatan Imaging Filter (GIF) have been used to study complex precipitation in commercial dual phase steels microalloyed with titanium. Titanium nitrides, titanium carbosulfides, titanium carbonitrides and titanium carbides were characterized in this study. Both carbon extraction replicas and thin foils were used as sample preparation techniques. On both the microscopic and nanometric scales, it was found that a large amount of precipitation occurred heterogeneously on already existing inclusions/precipitates. CaS inclusions (1 to 2 μm), already present in liquid steel, acted as nucleation sites for TiN precipitating upon the steel's solidification. In addition, TiC nucleated on existing smaller TiN (around 30 to 50 nm). Despite the complexity of such alloys, the statistical analysis conducted on the non-equilibrium samples were found to be in rather good agreement with the theoretical equilibrium calculations. Heterogeneous precipitation must have played a role in bringing these results closer together.

The strain relaxation in buried strained layers is investigated using an elastic continuum model. The mixture of single dislocations residing at the substrate/strained layer interface (lower interface) and dipolar dislocations in which one is at the lower interface and the other at the strained layer/capping layer interface (upper interface), is proposed. In the mixture, the dislocation distributions are denoted by a parameter which is the ratio of the density of misfit dislocations at the upper interface to that at the lower interface. In a buried strained layer, relaxation of mean strain occurs by introduction of two orthogonal arrays of mixture of single and dipolar dislocations. Considering both the free surface and interactions between dislocations, the total elastic energy per unit area of buried strained layer containing two orthogonal arrays of mixture of single and dipolar dislocations is calculated. The energy is dependent on the misfit dislocation distributions. On energy minimization considerations, the expression of the misfit dislocation distributions in a buried strained layer with arbitrary strain relaxation and capping layer thickness is derived. It is demonstrated that the strain is initially relaxed by the single misfit dislocations and relaxed by the mixture of single and dipolar misfit dislocations in the final stage of strain relaxation in many buried layers of practical interest.

The dielectric constant ε and the electrical conductivity σ were measured of crystalline plates cut perpendicular to the a-, b-, and c-axes from K2ZnCl4 (KZC) crystals, pure and doped with Co2+ ions, in the temperature range from 300 to 500 K. A pronounced broad peaks exists at the commensurate-incommensurate phase transition temperature (T c1). A thermal hysteresis of about 10 K is observed for the transition during heating and cooling processes. The J-E characteristics along the crystallographic axes were measured below and above T c1. Conductivity anomalies were observed at T c1. The results of electrical conductivity temperature measurements were analyzed and the activation energies of conduction at different temperature regions have been evaluated. The mechanism of the electrical conduction of the various phases and the anomaly at the transition point was discussed.

Bulk Y1Ba2Cu3Oy was melt-textured without the use of seedcrystals as well as by applyingtop-seeding with different seeds resulting in different orientationsof the c-axis.Samples were examined by elasticneutron scattering and levitation force.The levitation force of the samples stronglydepends on the orientation of the c-axis.The local superconducting parameters were found to bereduced with increasing distance from the seed.In order to study this influence,two cubes were prepared by top-seeding, butwith seeds of Nd123 that had a parallel and perpendicularorientation of the c-axis of the Nd123-seedwith respect to the contact area of the high-T c superconductor.By this, different distances of the levitating surface,which is the surface that faces directly the magnet, fromthe seed were obtained. Results are presented and discussed.

Under isostatic pressure aerogels display an irreversible shrinkage caused by plastic deformation. As a consequence of this plastic shrinkage it is possible to densify, and thus to modify the elastic properties of aerogels. We show that the elasticity of the material is strongly influenced by structural transformation, and we observe a weakening of the network during the first stage of densification. The structural evolution, followed by Small Angle X-ray Scattering, shows that the densification mechanism is different from the one obtained by a sintering at high temperature. The densification mechanism induces a textural change at the periphery of the constitutive clusters but not inside, in contrast to viscous sintering.

An argon Ion Beam Etching (IBE) simulation model has been developed to investigate the mesa profile evolution in III-V semiconductors' technology. Particular attention hasbeen focused on the sputtering yield angular dependence effect, on the influence ofthe material and 2D-morphology of the mask onto the pattern transfer. Experimentalsputtering yield versus ion incidence angle is injected into the simulation model.The equations which govern the surface evolution, stem from the current method of characteristics. The simulated profiles show that the trenching phenomenon can appearby only considering the variation of the sputtering yield versus the etched surfacecanting. This is obtained when neither the ion reflection nor the electric field linedeviation are taken into account. On the other hand, the slope transfer from the maskto the GaAs and InP substrates is studied.

An electronic speckle-pattern shearing interferometer (ESPSI) is proposed formeasuring the free convection heat transfer coefficient in liquids. The heattransfer coefficient may be deduced by a simple manipulation of the specklepatterns. Theory of the method as well as its application are presented. Themethod is robust and easy to use for non-skilled operators.

A procedure has been developed for the accurate measurement of film and substrate optical parameters from the multiple sample single-wavelength ellipsometric data. The dimensional reduction of the unknowns from newly formulated ellipsometric functions, the root selection and the thickness-dependent integer deduction enhance the rapidity of finding solutions and the convergence from a wide range of initial guesses while avoiding undesirable solutions. An error analysis carried out shows that the procedure is very resistant to the propagation of angular errors and allows the estimation of optimum film thickness ranges under which the parameters can be accurately found. The standard SiO2/Si structure is particularly studied using the procedure that is further illustrated with the experimental data on Ni/BK7-glass structures. The SiO2 film refractive index and thickness are thus shown to be accurately determined when sought along with the substrate optical constants. Moreover, the film and substrate real indexes are not altered in the presence of an interface layer between the film and the substrate while its existence is indicated by a systematic lowering of the Si substrate extinction coefficient. The procedure can be efficiently used in the continuous real-time optical characterization of films growing on substrates.

The pumping power dependent locations of the degeneration points were calculated for a plane-concave cavity. Such a simple experimental method for determining the degeneration points and their shifts due to thermal lensing is proposed. The laser beam patterns near the degeneration points were observed. For the pumping configuration under investigation the beam parameter product at the degeneration points increases considerably.

A comparative study on the emitter-base recombination current in different GaAlAs/GaInP/GaAs HBT structures including uniform base HBTs, and composition graded base HBTs, has been carried out. We have demonstrated that a graded base is not sufficient to prevent recombination on the base surface and that a thin GaInP ledge on the base surface reMayns necessary to retain a high enough current gain for small emitter high-frequency devices.

A method for determination of probability of electrical breakdown of gases ispresented in this paper and results are compared with theory. The method is based onthe measurements of breakdown time delay at different afterglow periods (relaxationtimes), where the secondary electron yield initiating breakdown is caused by residualactive states reMayning from the preceding glow. Measurements are carried out at lowpd (gas pressure times electrode spacing) of nitrogen and higher overvoltages up to2.1U s (U s: the static breakdown voltage). The experimentallydetermined breakdown probability is fitted by theoretical expressions for both theTownsend and streamer model of electrical breakdown, with particular attention to thehigher overvoltages. On the basis of our measurements and theoretical fit it can beconcluded that the Townsend mechanism is applicable at low pd value over the wholerange of overvoltage applied and a value of a secondary emission coefficient forgold-plated copper cathode is obtained. With the decrease of the breakdown probabilityand electron yield the distributions of delay times become broader and centered atlarger delay times, and the positive asymmetry and roundness increase.

We present a set of complementary experimental and numerical tools for studying miscible fluid displacements in porous media with large scale heterogeneities.Experiments are realized in transparent 2D Hele-Shaw cells allowing opticalobservations and in 3D packings of glass beads with an acoustical technique forimaging fluid displacements. Permeability heterogeneities are modeled by spatialvariations of either the local aperture of the Hele-Shaw cell or the diameter of thegrains used in the packing. The Hele-Shaw cell model provides high resolution maps ofthe invasion front location at regular time intervals and of the flow lines: thevelocity field is determined by combining these informations. Acoustical images ofrelative concentration distributions in the 3D packing are in agreement with Hele-Shawcell data and can be obtained in a broader range of experimental situations. Suchexperiments realized with a stabilizing density contrast between invading and displacedfluids demonstrate a strong reduction of the front width at low flow velocities, asimilar reduction is obtained at high velocities with a stabilizing viscositycontrast. The technique is also applicable to study fluid displacements in naturalopaque media. Numerical simulations by a Boltzmann lattice technique using aStokes-like diffusive term to smooth out the effect of permeability discontinuitiesprovide complementary informations. They are shown to give similar results asexperiments for same flow parameter values and to allow for a fast exploration of abroad range of fluid properties and flow situations.

From an analysis of the static friction regime of the tip of an atomic force microscope, a method is proposed for determining the viscoelastic modulus of materials which are viscoelastic at the temperature of the experiment. Present experiments consist in displacing the sample in its plane, periodically or at a constant velocity, while measuring the tangential force response of the contact to this shear solicitation. The proposed model permits to determine the relaxation and complex moduli at a sub-micrometric scale. Several experimental confirmations of the description are presented and it is shown that the local moduli measurements compare favorably with macroscopical results.

An experiment of high-frequency X-ray beam modulation for fast digital data transfer by X-rays is presented in this paper. The modulation of the beam is performed by diffraction on surface acoustic waves whose time-structure contains already the information to be transmitted. It has been possible to connect two computers via an X-ray beam and to perform digital data transfers at a speed of afew kbits/s.