Efficient method for optical constant determination by FTIR-ATR

Koji Ohta; Hatsuo Ishida

doi:10.1117/12.56372

1 March 1992 Efficient method for optical constant determination by FTIR-ATR

Koji Ohta, Hatsuo Ishida

Proceedings Volume 1575, 8th Intl Conf on Fourier Transform Spectroscopy; (1992) https://doi.org/10.1117/12.56372
Event: Eighth International Conference on Fourier Transform Spectroscopy, 1991, Lubeck-Travemunde, Germany

Abstract

We propose a novel iterative method to obtain optical constant spectra in the infrared region from FT-IR/ATR spectra. The algorithm consists of three steps. The first step is to obtain a trial extinction coefficient spectrum k(v) from a measured ATR spectrum, using the assumption that the two spectra are proportional to each other. The second step is the Kramers-Kronig (KK) transformation for obtaining the refractive index spectrum n(v) from the k(v) spectrum. The last step is a refining process of the k(v) spectrum using the calculated n(v) spectrum and the measured ATR spectrum. The last two steps are repeated until n(v) and k(v) spectra are stable. The present method adopts the most efficient algorithm at each step of the iteration. The rate of convergence of the iteration depends on the measurement conditions for the ATR spectrum and the maximum k(v) value. The use of germanium as a material for the internal reflection element (IRE), and 45 degrees as the incident angle, is found to give good convergence for the range of the k(v) values of most organic materials. This method is applied to several polymer films directly cast on the IRE prism from solution. The results are in good agreement with those obtained with other methods using transmission spectra.

Citation Download Citation

Koji Ohta and Hatsuo Ishida "Efficient method for optical constant determination by FTIR-ATR", Proc. SPIE 1575, 8th Intl Conf on Fourier Transform Spectroscopy, (1 March 1992); https://doi.org/10.1117/12.56372

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