This section demonstrates the simulation of an almost realistic reflectance unit. Devices like this are often used in the sample compartment of infrared spectrometers in order to record reflectance spectra of samples at various angles of incidence and different polarizations.
The SPRAY setup includes the following items: A circular light source emits divergent radiation directed towards a parabolic mirror. The light source is placed in the focus of the paraboloid - hence a parallel beam is created by the mirror. A second parabolic mirror creates a focus on a rotatable plane mirror.
In real spectrometers a Michelson interferometer - consisting of a beam splitter and a fixed and movable plane mirror - is usually placed between the two paraboloids. The interferometer is skipped in this setup because the performance of the reflectance unit is of interest here.
The plane mirror directs the radiation upwards onto an elliptical mirror. The center of the rotatable mirror as well as the sample position are the focal points of the ellipsoid. A second ellipsoid directs the beam reflected by the sample (here a perfect plane mirror is taken as sample) towards a second rotatable mirror. Finally the beam is focussed by another ellipsoidal mirror to the detector element which records the spectrum.
Here is a side view of the setup (with and without some test rays sent to visualize the function of the elements):
Viewed from the top the scenery looks like this:
