Phase-extraction analysis of laser-diode phase-shifting interferometry that is insensitive to changes in laser power

We investigate phase-shifting interferometry with a laser diode that is insensitive to changes in laser power associated with variations in current. A phase-extraction algorithm is newly developed in which the tested phase from six interferograms is measured. A formulation of the algorithm is presented by a least-squares fitting of the interference fringes to the function of the interferogram that includes intensity variations produced by changes in laser power. The performance of the algorithm is compared with the technique of Fourier analysis. A phase error caused by the power change of the laser diode is analyzed theoretically by use of the conventional phase-measurement algorithm and the Fourier-analysis technique. The systematic error is numerically investigated in comparison with the experimental result. A good agreement between them is shown. (C) 1996 Optical Society of America