Figure 7 shows a simplified schematic of a coherence peak sensing interference microscope. The
configuration shown in Figure 7 utilizes a two-beam Mirau interferometer at the microscope objective.
Typically the Mirau interferometer is used for magnifications between 10 and 50X, a Michelson
interferometer is used for low magnifications, and the Linnik interferometer is used for high
magnifications. A separate magnification selector is placed between the microscope objective and the CCD
camera to provide additional image magnifications. A tungsten halogen lamp is used as the light source.
Light reflected from the test surface interferes with light reflected from the reference. The resulting
interference pattern is imaged onto the CCD array. Also, output from the CCD array is digitized and read
by the computer. The Mirau interferometer is mounted on either a piezoelectric transducer (PZT) or a
motorized stage so that it can be moved. During this movement, the distance from the lens to the reference
surface remains fixed. Thus, a phase shift is introduced into one arm of the interferometer. By introducing a phase shift into only one arm while recording the interference pattern that is produced, it is possible to
performe itherp hase-shiftingi nterferometry or vertical scanningc oherence peak sensing interferometry.