Excitação óptica tipo degrau nas técnicas fototérmicas : estudo de vidros ópticos e de materiais para produção de energia

Abstract

In this work, four photothermal techniques, the Thermal Lens Spectroscopy (TL), the Thermal Mirror Spectroscopy (TM), the Photothermal Deflection (PDS), and the Open Photoacoustic Cell (OPC) have been employed to characterize several materials under tophat laser excitation. The experiments were performed on optical materials used for energy production. The theoretical models for the tophat laser excitation were developed for the TL and TM methods. Measurements on transparent optical glasses were performed concurrently with the TL and the TM techniques. The results have showed the feasibility of using less expensive non-Gaussian profile lasers for these techniques. Indeed, it has been showed that the TM tophat excitation can be used to study opaque solid materials. The measurements were performed on crystalline and polycrystalline graphite plates, which are materials used in hydrogen fuel cells. The feasibility of the TL under tophat excitation for the study of liquids was tested on diesel fuels extracted from Canadian oil sands. The results under tophat and also under Gaussian excitations were in good agreement and the values obtained for the thermal diffusivity and the temperature coefficient of the refractive index (dn/dT) were correlated with the cetane number and the monocyclic aromatics contents of the fuels. In addition, the OPC and PDS were used to characterize catalyst layers. Catalyst layers are materials also used in hydrogen fuel cells. In summary, the photothermal techniques under tophat laser excitation presented in this work have been proven to be applicable in studying several different materials, suggesting their applicability in less expensive setups compared to the Gaussian excitation.