Publications by authors named "Gustavo Torchia"

We report on a new methodology to track chain interdiffusion between polymer slabs based on Raman enhanced by plasmonic substrates. Diffusion is studied in a deuterated-polystyrene/polystyrene (dPS/PS) polymer pair, designed to provide a well-characterized diffusion behavior. The bilayer, 160 nm thick in total, is supported on a plasmonic substrate that provides local amplification of Raman signals in sample regions of close proximity to it. Gold-based substrates with structures of inverted pyramids, spherical nanoparticles and tipped pillars were investigated. Interdiffusion between dPS and PS is promoted upon annealing and followed in situ by dynamic spectral acquisition. A simple model that describes the coupling between the sampled region arising from the plasmonic effect and the diffusion process is employed to interpret spectral evolution data. It is shown that a highly regular topology and surface continuity are key features of the plasmonic substrate in order to provide reliable results. With pyramidal substrates, the most suitable substrates for this application, data are consistent with diffusion coefficients in the range 10-13-10-15 cm2 s-1 and dimensions of sampled regions below 40 nm. The strategy provides a reliable labeling-free technique to investigate polymer interdiffusion on the nanoscale.

We present a new method to determine Sr/Ca changes in hard dental tissues based on laser ablation and spectroscopic detection. By using femtosecond Laser Induced Breakdown Spectroscopy (fs-LIBS), we micro mapped the relative amount of strontium in the enamel of three human lower third molar. We also analyzed the Sr/Ca ratio along the striae of Retzius. Results show that microlibs allows detection of variation in relative Sr/Ca ratio through enamel. The same values of Sr/Ca ratio were found along a single stria. The method has a precision better than 95% and is sensitive enough to detect Sr/Ca ratio variations among striae and within stria. Fs-LIBS generates information in a fast and simple way that can be used by non-specialists to make inferences about diet or mobility in human populations and fossil hominids.

In this work, we present an alternative approach to angular velocity optical sensing based on two-ring resonators. This configuration admits the use of a standard laser diode source (0.1 nm, 10,000 MHz, FWHM) reaching higher sensitivities when narrow spectral laser sources (1 MHz, FWHM) are used. We compare this configuration with the standard single-ring resonator angular rate sensor (SRARS), which must use a narrow laser at input. Finally, we conclude that the sensitivity of this new approach can also be enhanced by coupling high-power broadband laser sources in a large range (from 1°/h to 10,000°/h), reaching performance similar to that of a standard SRARS configuration.

Near surface channel waveguides have been fabricated in Neodymium doped YAG ceramics by using IR femtosecond laser irradiation at the low frequency regime. Single mode guidance has been demonstrated with propagation losses of ~1 dB/cm. Time resolved confocal micro-luminescence experiments have been used to determine the spectroscopic properties of the Nd(3+) laser ions in the channel waveguide as well as to elucidate the waveguide formation processes.

We report production of nanoparticles of several advanced ceramics (Si3N4, SiC, AlN, and Al2O3) by ablation with femtosecond laser pulses of solid targets submerged in deionized water. The products withstand comparison with commercial nanoparticle suspensions obtained by other techniques as they are analyzed by means of transmission electron microscopy. As compared with metal nanoparticles produced with the same technique, we have found that the overall dependence of mean sizes and distribution widths on the laser fluence is similar. We explain why it is difficult to synthetize very small (<5 nm) and monodisperse particles in terms of ablation mechanism and discuss the aplicability of the technique for industrial production.