Phase-shifting Fizeau interference microscope with a wavelength-shifted laser diode

Abstract

A phase-measuring Fizeau interference microscopy with a laser diode (LD) source is studied that is based on a phase-shifting method using wavelengths varied stepwise by changing the current in the LD. The effect of the multiple-beam interference fringes on three kinds of phase-extraction algorithms is theoretically and numerically investigated. The phase error due to multiple reflections has a periodicity to one-fourth of the fringe spacing and a four-stepping method has the smallest error among interesting algorithms. The measurement error with a four-stepping method can be minimized by averaging two sets of measurements with an initial phase difference of π/4. This eases the adjustment of an initial phase by a tunable LD. A phase error caused by the power change in the LD is eliminated by normalizing the captured interferograms. Experimental results are presented with a Fizeau interferometer to show the usefulness of such procedures.