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Infrared Optics
The upper cassegrain is used for both visible light and infrared radiation. For this reason,
when you adjust the sample position so that the visible image of the sample is in focus, the
sample is also correctly positioned for collecting infrared spectra. Similarly, when you adjust
the aperture so that the required area of the sample is isolated visually, you have also
isolated the area of the sample from which the IR spectrum is to be collected.
IR optics in transmittance
IR optics in transmittance differs from when viewing a sample in transmittance as follows
(Figure 12):
Instead of receiving light from the illuminator, light from the spectrometer is reflected
•
off the toroid onto the lower dichroic mirror which sends it through the lower
cassegrain.
The upper dichroic mirror reflects the beam onto the detector cassegrain.
•
•
The detector cassegrain focuses the beam on to the detector.
Dichroic mirror
Variable
aperture
Upper
cassegrain
Sample position
Lower
cassegrain
Lower dichroic
mirror
Figure 12 Path of the Infrared Beam for Collecting an Image in Transmittance
NOTE: Figure 12, above, illustrates a Spotlight 200 with an MCT detector. Other detector
types may look different, but the optical arrangement is the same in all cases.
Overview of the Spotlight 200 . 37
Detector
Detector cassegrain
Source toroid
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