Fourier description of the phase-measuring process in two-wavelength phase-shifting interferometry

Abstract

Two-wavelength phase-shifting interferometry with dual frequency-modulated laser diodes has been investigated by using Fourier analysis. The phase shifts for each wavelength are produced by changing the wavelengths of the laser diodes through variation of the injection currents. The counter-stepping phase shifts introduce equal fundamental frequencies with opposite signs into two-wavelength interferograms. A Fourier description indicates that the phase difference between two wavelengths can be directly determined from the four-stepping algorithm presented in the interferogram domain. The frequency tunability in the laser diode can easily make the fundamental frequencies set required for the two-wavelength interferometry.