The technique of harmonic phase shifting interferometry (PSI), originally developed by Joseph Miceli in 19821, is a quasi-heterodyne method to continuously measure the optical phase of a point in an interferogram. The optical phase of the interferometer reference arm is modulated with the sum of prescribed amplitudes of a sine wave and its second harmonic. The interference phase at the detector is directly related to the electrical phase of the detected signal's fundamental frequency component. Harmonic phase-shifting interferometry may be executed by using a piezoelectric transducer (PZT) to shift the reference surface of the interferometer and a lock-in amplifier to measure the phase of the detected signal. Phase measurements may be made with peak reference arm phase changes less than 3λ/4, where λ is the wavelength of the light source, using either polarized or unpolarized light. This technique is best suited to single point measurements and line scans of interference patterns since each detector produces a continuous signal from which the interference phase must be extracted.
© 1992 Optical Society of AmericaPDF Article
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