Definition of Interactance
Three different measurement setups for obtaining near
infrared spectra are shown in Fig. 2. In reflectance mode
(Fig. 2a), light source and detector are mounted under a specific
angle, e.g., 45◦, to avoid specular reflection. In transmittance
mode the light source is positioned opposite to the detector,
while in interactance mode the light source and detector are
positioned parallel to each other in such a way that light due
to specular reflection cannot directly enter the detector. This
can be achieved by means of a bifurcated cable in which fibers
leading to the source and detector are parallel to each other and
in contact with the product, or by means of a special optical
arrangement (e.g., Greensill and Walsh, 2000a; McGlone et al.,
(Nicolai et al., 2007)
There is also similar definition of interactance by Karl Norris somewhere. May be in Davies Column but I cannot find it.
In the interactance mode
(Figure 6d) a higher probability is given to the incident
beam to interact with the sample. Consequently, the
emerging beam (collected at a place somewhat distant from
the location of incidence) contains more information on
the sample constituents and reflects better the actual
composition of the sample.
(Pasquini, 2003)
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