[en] During the adsorption of sulphur on Fe(100), Mo(110) and Pt(110) LEED patterns have revealed a series of surface compounds. Each compound is characterised by a well defined structure and stoechiometry. In models of structure based on hypothesis previously proposed by Huber and Oudar, each compound can be described by periodic arrays of such defects as vacancies. The influence of these defects on the reactivity is discussed, mainly in the case of Pt(110) poisoned by sulphur, in presence of carbon monoxyde and oxygen

[en] The growth of copper crystals on copper, by thermal decomposition of CuF₂, has been studied previously. It has been observed that, at a given temperature, the deposition rate reaches a maximum value which seems to be controlled only by the desorption of fluorine from a complete monolayer.Recent results concerning the thermal decomposition of TiF₄ and Ti and FeF₂ on Fe confirm this mechanism and give a measure of the heat of desorption of fluorine. The deposition rate can be generally improved if one uses the thermal decomposition of subfluorides. A method was developed based on sub-fluoride preparation in situ near the substrate. According to this new method, the formation of the sub-fluoride and its thermal decomposition occur simultaneously. This process is very suitable for the deposition of refractory metals at relatively low temperatures. Some examples are given, concerning mainly the decomposition of WF₅. Generally, in comparison with other halides, it seems that the thermal decomposition of fluorides is preferable for obtaining very high quality deposits, provided the technology necessary for fluorine chemistry is available

[en] A study has been made of the adsorption of sulphur on the (110) face of molybdenum using LEED and AES combined with a radioactive tracer technique employing ³⁵S. The content of the surface unit mesh can thus be determined precisely. By applying the 2D space groups, information can be obtained concerning the distribution of the adsorbed atoms. The hypothesis of a high symmetry has been assumed. In this case the observed patterns correspond to structures made of adjacent rows of occupied sites separated by one row of vacancies. (Auth.)

[en] We show that by using polarization coherent anti-Stokes Raman spectroscopy, the detection sensitivity of weak Raman modes is greatly enhanced. The spectra of the real part, the imaginary part, and the absolute magnitude of the resonant nonlinear susceptibility can be separately measured. Raman modes with cross sections as low as 2 x 10^-4 times that of the 992-cm^-1 mode of benzene are detectable with less than 10-kW-peak-power lasers

[en] Ag/Mo and Cu/Mo interfaces are created by evaporating a silver (or copper) thin film onto a (110) molybdenum single crystal. Growth takes place according to epitaxial relations and the interface is expected to be as coherent and clean as possible. Both samples are stable at all temperatures, in vacuum or in H₂, even under fast quenching or very long annealing. Under exposition to H₂S/H₂ mixtures, sulfur adsorbs on silver (or copper), diffuses through the thin film, and segregates at the interface. The segregated quantity, as measured by radiotracer techniques through the thin film, is found to be about one sulfur monolayer (7 x 10¹⁴ at/cm²) in both cases at low sulfur chemical potential. Such quantities, and the very accuracy of the results, indicate that segregated atoms are located precisely at the interface and even organized as a true monolayer, bound to silver (or copper) and molybdenum on its both sides. The presence of sulfur at Cu/Mo interfaces then induces a decomposition of the film into small crystallites which wet only partially the molybdenum substrate. Under classical assumptions, contact angle measurements lead to values of the shift of the interfacial energy caused by the segregated sulfur layer

[en] Four-wave mixing processes with double and triple resonances are discussed in detail. Explicit expressions for the resonant nonlinear susceptibilities of various cases are derived. It is shown that in some cases, four-wave mixing can yield a spectrum with reduced inhomogeneous broadening. Possible applications of multiresonant four-wave mixing as a spectroscopic technique are considered. They include high-resolution spectroscopy, deduction of transition matrix elements, study of transitions between excited states, measurement of longitudinal relaxation times, distinction between resonant Raman scattering and resonant fluorescence, etc. Selective polarization arrangement allows us to suppress the nonresonant background, separately measure the real and imaginary parts of the resonant nonlinear susceptibility, minimize the effects of absorption and laser intensity fluctuations, and greatly enhance the signal-to-noise ratio

No abstract available

[en] We report a fiber optical parametric oscillator (FOPO) synchronously pumped in a C-band, delivering high-energy picosecond pulses exceeding the nanojoule level of around 1700 nm. The gain medium is a dispersion-shifted fiber, pumped by highly-chirped pulses from a mode-locked dissipative soliton fiber laser. Optimizing the pump wavelength along with time-dispersion-tuning of the FOPO enabled a broad tunability from 1617–1876 nm for the idler wave. In addition, relative intensity noise levels below  −140 dBc Hz⁻¹ have been achieved, paving the way for using such a source in biophotonics and instrumentation. (letter)