Ricardo Castell

Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation

We present experimental results on the photoluminescence (PL) of gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL spectra in the UV spectral region correspond to the exciton recombination in the nanoclusters which are crystallized and cooled down to the temperature of the ambient gas in the ablation chamber. The time evolution of the spectra as well as their dependence on the ambient gas pressure are discussed.

Refractive index distribution measurements by means of spectrally-resolved white-light interferometry

Abstract A new procedure to measure the spatial distribution of the refractive index in transparent media is presented. It is based on the spectral analysis of optical interferograms obtained from a wide, continuous-spectrum light source. The method yields fairly high precision (up to 10-8) in the measurements of local values of differential refractive index, Δn (Δn=n−nref), along a line in the sample. By means of a CCD TV-camera linked to a microcomputer, fast recording and automatic data processing are achieved. As an application, we present an experimental study of a thermal gradient in a liquid sample.

Laser Ablation in the Synthesis of Zirconium Oxide

Results of an experimental study of the oxidation of a zirconium plasma generated by laser ablation of a metallic target under low pressures of oxygen are presented. The crystallographic identification of the collected product by electronic diffraction shows metastable ZrO cubic phase. The oxidation phenomena are interpreted by thermochemical simulation suggesting a model in accordance with other cases of synthesis of metastable oxides at high temperatures, such as plasma reactors.

Spatial and Temporal Behavior of a Laser Generated Titanium Plasma

Optical emission studies have been performed on the laser ablation of Titanium metallic targets. The high intensity radiation of a pulsed N2 laser (337.1 nm; 8 J/cm2) was focused onto the target to generate a short living (150 ns) plasma cloud that expands away from the surface into vacuum at high velocities. Time resolved measurements were taken as a function of the distance from the studied surface with a spatial rsolution of 20 µm, by collecting the emitted light in a direction perpendicular to the plasma expansion axis. A simple diffusion model with a “source” term is proposed to demonstrate the interaction of the laser beam with the plasma plume, as derived from analysis of the space-time behavior of several UV and visible atomic transitions.

Study of Sol-Gel Transition in Ceramic Systems by High Resolution Refractometry

Sol-gel methods are used to synthesize ceramic oxides for a wide range of applications in coatings, powders and monolithic pieces. The early stages of sol reactions, up to gelation, play an important role in the nanoscale microstructure, morphology and density of gels. This paper presents a recently developed interferometric method. A spectroscopic analysis of interferograms of white light passing through samples of sols, permits the precise measurement of gelation time up to 10 -7 s, and the geometrical positioning of the initial stage of the gel in the solution.