Optical waveguide writing with a diode-pumped femtosecond oscillator

Optical waveguide writing is demonstrated by means of a diode-pumped cavity-dumped Yb:glass femtosecond laser oscillator with a pulse energy of 270 nJ at a 166-kHz repetition rate. Waveguides realized on an Er:Yb-doped phosphate glass are almost perfectly mode matched to standard single-mode fibers at 1.55 microm and show a 1.2-dB net gain in a standard telecommunications amplifier setup. Waveguide writing with a compact femtosecond laser oscillator is an important step toward introducing this technique into an industrial context.     

Band gap formation and multiple scattering in photonic quasicrystals with a Penrose-type lattice

This Letter presents a study of the local density of states (LDOS) in photonic quasicrystals. We show that the LDOS of a Penrose-type quasicrystal exhibits small additional band gaps. Among the band gaps, some exhibit a behavior similar to that typical of photonic crystals, while others do not. The development of certain band gaps requires large-size quasicrystals. It is explained by the long-range interactions involved in their formation. Moreover, the frequencies where the band gaps occur are not necessarily explained using single scattering and should therefore involve multiple scattering.     

Fragmentation of neutral Cn clusters (n = 9): experimental and theoretical investigations

We report on experimental and theoretical efforts designed to understand the fragmentation of small carbon clusters. Experimentally, a new detection system for high velocity fragments has been recently developed allowing the fragmentation of high velocity clusters to be totally recorded [1]. Results for the branching ratios of deexcitation of C₅ and C₉ formed by electron capture in high velocity collisions are presented. Theoretically, the dissociation dynamics of C₅ has been investigated using a kinematical model based on the statistical theory of Weisskopf. In this model various structural quantities (geometries, dissociation energies, harmonic frequencies), are required for both the parent cluster and the fragments. They have been calculated within DFT and coupled-cluster formalisms for C_n up to n = 9. In all cases, a strong correlation between measured branching ratios and calculated dissociation energies is observed.     

A new program based on stochastic Liouville equation for the analysis of superhyperfine interaction in CW-ESR spectroscopy

In the slow-motion region, ESR spectra cannot be expressed as a sum of simple Lorentzian lines. Studies of Freed and co-workers, on nitroxides in liquids gained information on the microscopic models of rotational dynamics, relying much on computer programs for simulation of ESR spectra based on the stochastic Liouville equation (SLE). However, application of Freed's method to copper system of biological interest has been for a long time precluded by lack of a full program able to simulate ESR spectra containing more than one hyperfine interaction. Direct extension of the Freed's approach in order to include superhyperfine interaction is not difficult from a theoretical point of view but the resulting algorithm is problematical because it leads to substantial increase in the dimensions of the matrix related to the spin-hamiltonian operator. In this paper preliminary results of a new program, written in C, which includes the superhyperfine interactions are presented. This preliminary version of the program does not take into account a restoring potential, so it can be used only in isotropic diffusion conditions. A comparison with an approximate method previously developed in our laboratory, based on a post-convolution approach, is discussed.     

Analytical properties of the amidoxime group. XII

Journal of Thermal Analysis and Calorimetry - The acid-base equilibria of succinediamidoxime (SIDA) were studied by means of potentiometric and thermometric techniques. RefinedpK values (pK...     

EPR characterization of new phosphavinyl σ radicals

A number of radicals have been added to 1,3-bis(2,4,6-tri-tert-butylphenyl)diphospha-allene at low temperature in cyclopropane solution. Addition of thiyl and alkoxyl radicals occurs regiospecifically to one of the phosphorus atoms leading to new phosphavinyl radicals, isoelectronic with vinyl radicals, which have been characterised by means of EPR spectroscopy. The results of ab initio calculations are in agreement with the experimentally determined spectral parameters and suggest that these radicals are bent, with a PCP bond angle of ca. 150°. In contrast, silyl and germyl radicals appear to add to the carbon atom of the phosphaallene.     

Abnormal behaviour of some parameters revealed in the Georgian SSR before the Armenia earthquake of December 7, 1988: a preliminary report

Summary For more than ten years several measurements sites able to detect geophysical and geochemical precursory phenomena of earthquakes have been working in Soviet Georgia. On the occasion of the destructive Armenia earthquake of December 7, 1988 (M=6.9) premonitory signals relative to geophysical and geochemical parameters seem to be observed. In this paper anomalous variations of the water level in a well, of the helium content in thermal waters and of the electromagnetic signals in air, obtained in three measurements sites located at about 80 km from the epicentre, are reported. These variations appear beginning from about a month up to some hours before the occurrence of the earthquake and it seems reasonable to consider them as short-time or very short-time precursory phenomena of the earthquake.     

Weighted approximation of functions by Szász--Mirakyan-type operators

Summary We give error estimates for the weighted approximation of functions with singularities at the endpoints on the semiaxis by some modifications of Sz\'asz--Mirakyan operators. To do so, we define a new weighted modulus of smoothness and prove its equivalence to the weighted K-functional. Also, the class of functions for which the modified Sz\'asz--Mirakyan operator can be defined will be extended to a much wider set than for the original operator.     

Optical properties,structure and electronic energy levels of the organicN-methyl, 2,3 diphenyl, 5-methyl indole compound

Summary The absorption properties of the new synthetized organicN-methyl, 2,3 diphenyl, 5-methyl indole compound have been studied. An X-ray diffraction analysis has been carried out in order to obtain the structural properties and the density of the material. Optical absorption spectra have been interpreted on the basis of a CNDO calculation of the energy levels. The results show a good agreement between theory and experiment. Work partially supported by Ministero della Pubblica Istruzione through CNR-CISM.