Fresnel Reflection from Bulk Samples

FRESNEL REFLECTION FROM BULK SAMPLES 13.2.1. Fresnel Equations... 

One note of caution should be sounded. If radiation is scattered from the interior of the sample, as might be the case because of the presence of a filler in the bulk of the sample, diffuse reflection (see Chapter 16) will take place along with the Fresnel reflection. In this case, the Kramers-Kronig transform will not yield an accurate estimate of the n and k spectra. One indication that diffuse reflection is contributing to the spectrum is that the bands in the fe spectrum calculated from a given reflection spectrum are asymmetric. 

Diffuse reflection (DR) spectra result from the radiation incident on a powdered sample that is absorbed as it refracts through each particle and is scattered by the combined process of reflection, refraction, and diffraction. That fraction of the incident radiation that reemerges from the upper surface of the sample is said to be diffusely reflected. Because DR spectra result from an absorption process, they have the appearance of transmission spectra (i.e., bands appear in absorption), unlike the case for Fresnel reflection spectra of bulk samples (see Chapter 13). When DR spectra are acquired on Fourier transform spectrometers, the singlebeam spectra of the sample and a nonabsorbing reference are measured separately and ratioed to produce the reflectance spectrum, Rfy). 

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