Espectroscopia não linear em cristais fluoretos e polianilina / Nonlinear spectroscopic characterization in fluoride crystals and polyaniline

AUTOR(ES)

Viviane Pilla

DATA DE PUBLICAÇÃO

2001

RESUMO

In this work we studied the effect of nonlinear refraction in Cr+3 doped fluoride host crystals and polymers. The fluoride crystals have been attractive due a broad emission bandwidth and a tunable solid-state lasing in the range of approximately 780-1010 nm. Applying the Thermal Lens (TL) technique, we accomplished a quantitative study of the behavior of the quantum efficiency, in the presence of the processes of the fluorescence thermal quenching and upconversion processes. We introduced a new method of application of the TL technique, which makes possible the determination of the quantum efficiency as a function of the saturation parameter S (S= IM/Is, where IM is the medium intensity in the material and Is, the saturation intensity). Based on those results it is possible to determine the Auger upconversion parameter (γ), it one knows the total population of Cr+3 (N0) and the emission lifetime τ(τ-1=τR-1+τNR-1) of the investigated material. This method is presented for 1% and 7% Cr+3 doped LiSAF, and 4.7% of Cr+3 doped LiSGaF, upon excitation in the cw regime at 15°C. In the case of the polymers, we studied the nonlinear properties (electronics and thermal nonlinearities) of the polyaniline samples (PANI) doped and nondoped with H2SO4 in the film form and dissolved in dimethylsulfoxide. We used the LT (cw) and Z-scan (cw and pulse of 70 ps) techniques. The measurements were accomplished as a function of the concentration of PANI and temperature. Using a laser of Nd:YAG with pulse trains, we accomplished the dynamic behavior of the optical nonlinearity as a function of the PANI concentration. By this method we were able to discriminate between electronic and thermal lensing nonlinearities, and allows the determination of the nonlinear refractive index (n2f) and thermal index (n2cth) that is related to the thermal parameter dn/dT (temperature coefficient of refractive index).

ASSUNTO(S)

polianilina fluoride crystals cristais fluoretos thermal lens lente térmica polyanilina

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