Modulateur electrooptique pour l'extraction d'une impulsion lumineuse d'un train

The performance of a new light modulator are presented. It uses the Pockels effect in order to select a single pulse from a train. The repetition rate of commutation is greater than 100 Hz, the contrast ratio exceeds 10⁴ and the lifetime is about 5 x 10⁷ shots. The main advantage of this modulator is an easy working-up.     

Réalisation d'un simulateur de corps noir pour l'étalonnage absolu des détecteureurs de flux lumineux

For the purpose of absolute calibration of luminous flux detectors against a grey thermopile, a primary standard has been built which is a blackbody simulator having a conial cavity observed along a parallel to its axis.     

Etude spectroscopique d'un jet de plasma d'argon hors d'equilibre thermodynamique local

We have studied the properties of an argon plasmajet seeded with a few percent of hydrogen. At atmospheric pressure, significant deviations from local thermodynamic equilibrium (L.T.E.) are shown. The plasma parameters (electrondensity N_e, temperature T) have been determined from the broadening and the absolute intensity of hydrogen lines. The transition probabilities and the broadening parameters (width and shift) of some AI lines between 4000 and 6000 Å have been measured.     

Balayage d'un laser a colorant continu monomode sur 150 GHZ

Continuous single mode scans of the frequency over range greater than 30 GHz in c.w. ring dye lasers is a challenge due to the lock of tracking of the thin solid intracavity Perot-Fabry etalon. We here present a device allowing to overcome such difficulties and single mode continuous operation in scans up to 150 GHz frequency range.     

Influence de dipoles magnetiques sur le parametre d'ordre d'un supraconducteur

It is shown that the order parameter of a superconductor containing insulated magnetic dipoles depends on the mean magnetisation of the sample. The model agrees with the results observed experimentally.     

Influence d'un fort champ electrique statique sur le spectre d'absorption du polyester mylar

Electrical fields induce a shift towards lower frequencies of the absorption spectrum of mylar, this shift, proportional to the square of the field, is three orders of magnitude smaller than a typical Franz-Keldysh effect and is sensitive to the relative orientation of the static field with respect to the polarization vector of the light. We suggest that the measured shift is mostly due to Stark effects in this amorphous material. This kind of measurement could be used to estimate the degree of crystalline order in partially amorphous solids.     

Determination des angles d'obliquite d'un cristal liquide en phase nematique au voisinage d'une surface

Using several laser sources the dispersion of the quadrupole nonlinear tensor d⁽²⁾(CaCO₃) has been determined in the ultraviolet and visible range 265 – 592 nm. The measured dependence is in a good agreement with the predicted dispersion d⁽²⁾(CaCO₃) ~ λ^-1.     

Études de spirales d'évaporation sur des cristaux d'anthracène

The imaging of evaporation structures on vacuum-cleaved surfaces of anthracene single-crystals is obtained by means of nucleation-decoration method first developed by Bassett. From the micrographs of decorated steps some information is available on the obtained structures: step heights, anisotropy of the steps moving. The shape of the evaporation spirals reveals an asymmetrical dissolution kinetic caused by the presence of two kinds of opposite steps along [100].     

Etude des effets spectraux et spatiaux liés à la propagation d'un faisceau laser resonnant dans une vapeur de baryum

We present some characteristic features of the interaction between a resonant laser pulse and a dense atomic medium (barium vapor). A spectral analysis of the coherent transmitted light displays side bands related to the Rabi frequency. A study of the spatial behaviour of the laser beam shows that light filaments are generated and we specify in what experimental situation (light intensity, atomic concentration) this phenomenon takes place. Starting from Maxwell-Bloch equations for a resonantly driven two-level atomic system we built a computation code whose numerical results are in good agreement with our experiments.     

Etude du chromatisme d'un systeme optique par photographie “speckle”

Speckle photography experiments have been used for studying optical systems and more recently we have used image speckle photography to measure displacements and deformations of a partial diffuser. The same method is now used for studying chromatic aberrations of a lens system. Experimental results are given for three optical lenses.     

Etude spectroscopique de l'effet d'anode

Spectral lines of LiI emitted by an anodic plasma, produced during electrolysis of a KCl-LiCl mixture, have been observed. This paper deals with diagnostic studies of this plasma and is based on a comparison of observed line profiles for LiI(2P-3D), (2P-4S) and (2P-4D, 4F) with calculated values derived from the Griem-Baranger impact theory. We have found, from the ensemble of the results, that the electron density in the plasma center is N_e(0) ? 1·8×10¹⁷ cm^-3, the electron temperature is T_e(0) ? 9×10³ °K, and the plasma thickness is l ? 200 μ.     

Autocorrelation d'un diffuseur depolarisant

The autocorrelation of a depolarizing diffuser illuminated successively by two linearly polarized beams of light is proportional to the cosine of the angle between the directions of polarization. The speckle pattern exhibits the same properties of correlation.     

Utilisation des franges d'interference en lumiere diffuse pour l'etude de l'etat de surface d'un diffuseur

A diffuser, illuminated successively by light of two neighbouring wavelengths, produces on a photographic plate placed in a parallel plane two intensity distributions which are homothetic except for certain decorrelation terms. This homothecy (scale variation) can be compensated by a longitudinal displacement of the photographic plate between the two exposures and consequently, the decorrelation depends only on the structure of the diffuser. Under these conditions, if the photographic plate is given an additional displacement in its own plane between the two exposures, the contrast of Young's fringes obtained in the Fourier plane characterises the roughness of the diffuser.     

Modification de l'absorption hertzenne d'un gaz sous l'action d'un champ infrarouge non resonant

With non-resonant infrared laser radiation, a frequency shift of the microwave absorption line of ammonia is observed. The experimental data are in good agreement with the theory of the Stark effect in a rapidly-varying field.     

Accroissement d'energie interne et de densite d'energie interne d'un milieu dielectrique polarise

For an isotropic dielectric medium, having an arbitrary shape and a stationary polarization, the polarization-induced increase of internal energy of the dielectric only is reexamined from Güntelberg's thermodynamic point of view. The value obtained for this increase is quite different from what was previously admitted, even in the case of dielectrics with simple shapes. The new value is in better agreement with earlier results. It is furthermore well in accord with the exact macroscopic relation between the internal energy and a density of internal energy, a relation which is more intricate than the simple relation of integration largely accepted up to now.     

Etude par spectrometrie Raman des complexes de l'iode dans les alcools et les ethers

Laser Raman spectra of iodine-alcohol and iodine-ether solutions have been studied. It was found a new line at 167 cm^?1 for alcohols and at 170 cm^?1 for ethers which is tentatively attributed to an intermediate Hassel complex.     

Biaxialite critique d'un smectique C

Measurements of the biaxiality of a smectic C as a function of the order parameter are presented for n-heptyloxybenzylidene-n-heptylanisol at the second order transition smectic A to smectic C. The experimental set up is a variation of the classical conoscopy method of interference.     

Sur la contribution des differents porteurs à la zone de charge d'espace d'un semiconducteur multivallée

We study, in the case of the parabolic approximation, the space charge of a two-valley conduction band semiconductor; the electrons associated to these valleys are supposed to have different effective masses. By using a non-degenerate distribution we analyse the contribution of the different carriers to the space charge and the effect of surface band bending, temperature, effective masses, dope and type of material. We point out that the space charge can be governed by either type of carrier or both. By comparing the results with those given by a single valley model, we show the incidence of the initial hypothesis on the value and evolution of the space charge with temperature and surface band bending. As an exemple, we study briefly n-type GaSb.