PerkinElmer Spotlight 400 Series, User Manual

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Techniques for Collecting IR Images and Spectra . 93
The greatest limitation to this method is the presence of an interfering diffuse reflection
signal. This occurs when the sample surface is not perfectly smooth. The Kramers-Kronig
integration is not appropriate for spectra from such samples.
Reflection-Absorption
NOTE: Reflection-absorption is mainly applicable to mid-infrared applications.
Reflection-absorption occurs when the incident radiation passes through a thin, absorbent
film that is on a reflective surface (typically a metal) and is then reflected back through the
film (Figure 35). The absorbance spectrum of the film can be collected directly. Figure 38
shows the spectrum of residual oil on an electronic contact. The sample diameter was
100 µm.
Figure 38 Reflection-absorption spectrum of residual oil on an electronic contact