Determination of Optical Constants
Internal reflection spectroscopy (IRS) has attributes that make it particularly suitable to the determination of the optical constants. They demonstrated that the sensitivity of the IRS technique permitted the determination of the optical constants for weakly absorbing materials. Plaskett and Schatz have shown that in this case the Kramers- Kronig transformations may be used to establish a relationship between the phase shift of the reflected radiation and the reflection coefficient. The refractive index decreases, reaches a minimum and then increases sharply, and reaches a maximum and decreases to its original value, as wavelength increases across the absorption band. The large distortion of the spectra in IRS in the vicinity of the critical angle is an example of the dispersion of the reflectivity across an absorption band. The effect on the spectra as the angle of incidence approaches and crosses the critical angle as demonstrated by Mirabella.