Scanning technique for obtaining linear fringe shift readout from a high resolution interferometer

A technique is described for obtaining a linear readout of fringe shift from a high resolution Fabry-Perot interferometer. One mirror of the interferometer is mounted on a piezoelectric crystal driven by a high frequency sinusoidal voltage. A signal proportional to the mirror displacement is displayed on the Y axis of an oscilloscope, while the X axis is swept with time. Each time the interferometer passes through a transmission maximum, a pulse is produced which is fed to the Z axis of the oscilloscope, producing an intensified dot. The displacement of the resultant row of dots from its ambient position is linearly proportional to the fringe shift occurring within the interferometer, has no sign of ambiguity, and is independent of the finesse. All the circuits required for producing the readout were realized using the internal circuitry of a standard laboratory oscilloscope.