Angulo Vinuesa, X.; Bacquet, D.; Martín-López, Sonia; Corredera, Pedro
Raman-assistance (RA) has been identified as a promising technique to extend the measurement range of Brillouin optical time-domain analysis (BOTDA)-based distributed sensors. Unfortunately, Raman amplification introduces a great amount of relative intensity noise (RIN) to the detected low-frequency probe wave. This RIN transfer problem has been widely identified as a major limitation in RA-BOTDA. In vector BOTDA (VBOTDA), the detected signal is transferred to a high-frequency carrier where the Raman RIN transfer turns out to be much less harmful. In addition, a VBOTDA can also provide information about the phase-shift induced by the local stimulated Brillouin scattering gain curve, paving...
Gómez-Sánchez, Antonio; Stiefel, Berta M.; Fernández-Fernández, R.; Pascual, Conrado; Bellanato, Juana
Acetoacetic esters and pentane-2,4-dione undergo unusual Michael reactions with β-nitrostyrene in methanol-sodium methoxide to form the(2R,3R,2′S,3′S)-bis-(4-acyl-2,3-dihydro-5-methyl-3-phenyl-2) -furylhydroxylamines (5) in high yields. The normal adducts (6) are intermediates in these reactions. Acetylation of compounds (5) gives the hydroxylamine O-acetates (7). Compounds (5) react with ammonia and amines in methanol to give the 3-acylpyrroles (9) which can be isolated in high yields. These pyrroles can be easily obtained in high yields in a one-pot process by reaction of the 1,3-dicarbonyl compound with β-nitrostyrene and subsequent treatment of the reaction mixture with ammonia or amines. A mechanism for the formation of the unusual...
Nalda, R. de; Silva, Diego; Siegel, Jan; Solís Céspedes, Javier; Castillejo, Marta
Multiphoton dissociation undergone by the organosilanes 2-chloroethenylsilane and phenylsilane upon irradiation with laser pulses of 20 ps and 4ns duration at 290 nm has been studied through detection of their spontaneous fluorescence. Atomic Si (4s 1S0 1) emissions are reported, together with the Swan bands of C2. Additionally, SiH2 formed in a two-photon process was observed by laser-induced fluorescence techniques in the photolysis of 2-chloroethenylsilane. The results show a strong selectivity when compared to those obtained previously for far UV irradiation around 200 nm and provide insight into the nature of the photodissociation mechanisms, where the SiH2 fragment plays a...
Pivin, J. C.; Jiménez de Castro, Miguel; Hofmeister, H.; Sendova-Vassileva, M.
The efficiencies of three methods based on a combination of sol-gel chemistry and ion implantation for obtaining an optical activation of Er atoms via the transfer of excitons energy are compared. A better coupling is observed in silica-gel containing Er prepared by addition of Er nitrate to the tetraethoxysilane sol and embedding Si nanocrystals formed by ion implantation or in a silicon suboxide derived from triethoxysilane and implanted with Er ions than in silica-gel implanted sequentially with Si then Er. The infrared emission of Er ions is reduced by the segregation of erbium oxide or the precipitation of Er5Si3, depending...
Castillejo, Marta; Martín, Margarita; de Nalda, R.; Solís Céspedes, Javier
The multiphoton dissociation of ketene at 308 and 290.5 nm has been studied using different laser pulse widths of 15 ns, 4 ns and 10 ps by observing the photofragment fluorescence in a static cell. Efficient emission from CH(A 2Δ) and (B 2Σ-) was detected in both nanosecond and picosecond experiments. C2 Swan bands were observed only with nanosecond pulses. These results are discussed invoking the competition between multiphoton absorption by the parent molecule and dissociation into possible intermediate photofragment precursors.
Gonzalo de los Reyes, José; Afonso, Carmen N.; Ballesteros, J. M.
Space-resolved real-time emission spectroscopy and in situ reflectance measurements during film growth are used to characterize the plasma expansion dynamics and the refractive index of films produced by laser ablation of BaTiO3, respectively. The refractive index of the films remains nearly constant when increasing the gas pressure up to a pressure threshold above which it increases sharply, similar results being obtained either in oxygen or argon. This behavior is correlated to the changes observed in the plasma expansion dynamics; the results being discussed in terms of the dependence of the length of the plume on the gas pressure and the...