Reflectance units like the one discussed here are often used in combination with ATR (attenuated total reflection). If a multiple reflection ATR crystal made of silicon is placed at the sample position the situation is this:
Here is a side view of the setup:
Obviously the ATR crystal has to be moved up in order to work properly because the radiation has to enter the crystal from the 45° edges. In order to find the best position we can let SPRAY do the work, controlled by OLE automation commands from Excel's VisualBasic in this case. Varying the height of the ATR element and recording the detector signals one gets the following results:
Trying a z-value of 0.33 seems to be promising. In fact, the light throughput is much better now:
There are 5 total reflections at the bottom side of the ATR element on the average:
