PerkinElmer Spotlight 150, User Manual

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92 . Spotlight 150 User's Guide
As the sample is diluted in a non-absorbing matrix (KBr), specular reflectance is minimized.
The bottom spectrum more closely matches an absorption spectrum.
NOTE: Sample cups for obtaining diffuse reflectance spectra of powders are available from
PerkinElmer: regular cup (part number 01862760), micro cup (part number
01862761).
Figure 41 Diffuse reflectance spectra of PMMA
Specular Reflectance
Specular reflectance is reflection in one direction (Figure 40). This is the type of reflection
that occurs from a smooth, polished surface.
Absorption information cannot be obtained directly from a specular reflectance spectrum of a
dielectric material, because the reflectance spectrum is governed by dispersion in the
refractive index. However, you can use the Kramers–Kronig integration to calculate the
absorbance spectrum from the specular reflectance spectrum. This integration is performed
by the Kramers–Kronig process in Spectrum.
Figure 42 Specular reflectance spectrum of a PMMA plate and the absorption
spectrum calculated from it with the Kramers–Kronig process in Spectrum