Strong ion migration in shown to enable the production of high refractive index contrast waveguides by fs-laser writing
in a commercial (Er,Yb)-doped phosphate based glass. Waveguide writing was performed using a high repetition rate fslaser
fibre amplifier operated at 500 kHz and the slit shaping technique. Based on measurements of the NA of
waveguides, the positive refractive index change (Δn) of the guiding region has been estimated to be ∼1-2 x10-2. The
compositional maps of the waveguides cross-sections performed by X-ray microanalysis evidenced a large increase of
the La local concentration in the guiding region up to ~25% (relative to the non-irradiated material). This large
enrichment in La was accompanied by the cross migration of K to a neighbouring low refractive index zone. The
refractive index of the La-phosphate glass increases linearly with the La2O3 content (Δn per mole fraction increase of
La2O3 ≈ 5x10-3) mainly because of the relative mass of the La3+ ions. The density increase without substantial
modification of the glass network was confirmed by space-resolved micro-Raman spectroscopy measurements showing
minor variations in the (PO2)sym vibration Raman band. These results provide evidence for the feasibility of adapting the glass composition for enabling laser-writing of high refractive index contrast structures via spatially selective
modification of the glass composition.
A study of the fluorescence and Raman spectra of a new and complex drug delivery system formed by emodin adsorbed on silver nanoparticles embedded into a matrix of porous silicon is here reported. Several experimental methods of inclusion of the drug-silver set inside the pores, without previous functionalization of porous silicon, have been tested in order to optimize the conditions for the fluorescence detection of emodin. In this sense, we have also added bovine serum albumin to the system, finding that the presence of the protein enhances the fluores-cence signal from emodin.
Metal nanostructures are known to amplify the spontaneous emission of fluorescent molecules by resonant coupling to external electromagnetic fields. We have used spectroscopy to characterize the structural properties of emodin molecules, a natural anthraquinone dye, and bovine serum albumin, the most abundant protein in plasma, in the presence of silver nanoparticles. Aggregation of emodin at pH=10 and pH=6 gives rise to SERS and MEF effects in silver colloid. We have obtained MEF spectra at acidic pH=2.9 using two different silver nanostructures. We have also studied the change in the secondary structure of bovine serum albumin adsorbed on metal nanoparticles surface. Circular dichroism, fluorescence emission and fluorescence lifetime measurements indicate an increase in the alfa-helical content of the protein and a change in the environment of the tryptophan residues that bury in the interior of the biomolecule. This variation on the secondary structure could have further influence in the binding of the drug to form transport and regulatory complexes.
Low frequency modulated N2O hollow cathode discharges have been studied using time-resolved FTIR absorption and emission spectroscopy. Some experimental absorption data corresponding to slow transients of the discharge, as well as the temporal behavior of the different bands observed in the emission spectra, are presented here. A general exposition of the chemical reactions included in the kinetic model that explain with a satisfactory agreement that experimental stationary and time-resolved data is also given.
The study of the different experimental variables affecting the dissociation processes of molecular species, when using hollow cathode discharges as excitation method, and the characterization of the corresponding plasmas, have been made using FTIR absorption and emission spectroscopy. Mass spectrometry has also been employed for diagnosis purposes. The availability of step-scan mode and time resolved possibilities in our FTIR spectrometer, allowed to follow the excitation processes when using modulated discharges. Nitrous oxide, N2O, for which no data in hollow cathode discharges were available, has been employed as test compound for checking the possibilities of our experimental setup.
Two new double modulation techniques for infrared absorption spectroscopy of transient molecules are described. Both of them are based in the modulation in concentration of the unstable species and the modulation in amplitude of the laser radiation. One of the methods is specific for short lived transients; the first results obtained with it for the H3 + spectrum are given. The other one is more suitable for longer lived species; it has been applied to the study of the 113 band of CH3 and vibrational excited states of methane.
High resolution stimulated Raman spectra of the Q branches in the regions of the (nu) 1 and (nu) 3 Raman active modes of ethane 12C2H6) have been recorded. A complete analysis of the (nu) 3 region in terms of a vibrational torsional coupling has been achieved. For the (nu) 1 region spectra at 300 K, 173 K (static) and 30 K (jet expansion) have been recorded. On the basis of the 30 K spectrum, a preliminary assignment of the strongly perturbed spectra is presented.
Using an original double modulation set-up of an IR difference frequency laser spectrometer and a hollow cathode discharge cell with methane, in addition to a double phase sensitive detection method, it has been possible to distinguish between (nu) 3 band spectral lines of the CH3 radical and the much stronger lines belonging to the C-H stretching bands of the precursor and other stable species (C2H4, C2H6) that appear in the discharge. The method has proved to be very sensitive to detect population variations versus temperature of very weak transitions from highly excited levels of CH4 and other stable species. The temperature characterization of several neutral species involved in the hollow cathode discharge has been tested and remarkably low temperatures have been obtained.
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