The photodiode is the detector here. Measurements reflect changes in the intensity of light at the photodiode. The laser light moves over the surface. The light reflected from the surface is measured by the computer which calculates a 3-dimensional picture of the surface. The plots shown here are for the surface of a steel sheet which came straight from the mill without polishing.
Valleys are dark, and humps are lighter in color.
Note the instrument measures 0.5 micron in depth at these settings. The area scanned here is 80 microns on a side. Students are asked to compare an analysis of a standard to NIST statistical data to pick out poor points and access where problems might be in the analysis. Select Analytical Method Students are asked to select the best method of analysis when presented with a picture of a steel sample. Although the activity is multiple choice, the decision making is similar to that in a laboratory.