Obtenção de constantes opticas no infravermelho a partir de medidas de reflectancia especular via analise de Kramers-kronig

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

Kramers- Krönig analysis, which correlates the real and the imaginary parts of causal complex functions, provides the reconstruction of the phase shift spectra from reflectance spectra, when appIied to the complex specular reflectivity. Fresnel s formulae, by their turn, permit the calculation of the optical constants, refractive and absorption indexes, from the reflectance and phase shift spectra. In the present work, Kramers-Krönig analysis was carried out by two different methods: (i) the conventional, through Hilbert transformation and (ii) the one proposed by Peterson and Knight, in which the analysis is carried out by two successive Fourier transformations, the so-called Fourier s allied integrals. The analysis was restricted to the following assumptions: the incidence angle was close to the normal and the sample had semi-infinite thickness so that the observed reflection could be attributed only to the first air/sample interface. With such a target, two programs were built in the software MatLab for Windows of the Mathworks Incorporation, using the above-mentioned methods. The performance of both programs were assessed by means of simulated reflection spectra, obtained by Lorentz s dispersion model and, afterwards, by means of experimental spectra of benzoic acid, phtalyc anhydride and vitreous silica. The performances of both programs were satisfactory and similar to each other. However, the program based in the Fourier s allied integrals showed several advantages over the conventional one, such as computation time and further possibilities of checking the physical reIiability of the input data.

ASSUNTO(S)

espectroscopia de infravermelho otica refração

ACESSO AO ARTIGO

Documentos Relacionados