Non linear phase shift calibration for interferometric measurement of multiple surfaces

In a wavelength-tuned phase shifting interferometer, a method for producing a constant phase shift speed for data acquisition including the steps of:

• providing a tunable coherent light source in an interferometer;
• placing a single reflective surface at the location of a test piece in the interferometer;
• coupling a phase shift driving mechanism to the light source to control the wavelength of light emitted therefrom;
• supplying a known input to the phase shift driving mechanism to acquire a set of interferograms from the interferometer;
• determining a temporal phase shift speed from the set of interferograms;
• generating a new known input to the phase shift driving mechanism for acquiring another set of interferograms with the temporal phase shift speed, the known input, and the desired phase shift between adjacent interferograms;
• and
• using the input which produced the predetermined desired phase shift obtained from a single reflective surface as a final input for application to the phase shift driving mechanism to produce substantially linear phase shifts of the interferograms produced by the interferometer.