2-WAVELENGTH LASER-DIODE INTERFEROMETRY THAT USES PHASE-SHIFTING TECHNIQUES

Two-wavelength phase-measuring interferometry with dual laser-diode sources has been developed that is based on a phase-shifting method that uses two wavelengths varied stepwise by separately changing the currents in two laser diodes. A synthetic wavelength is produced by the addition of two single-wavelength interferograms without the need for auxiliary techniques. The phases are equally shifted in opposite directions to each other on an unbalanced interferometer. The fringe shifts that result from modulated phases are monitored with an electronic sensor to ensure accuracy. Our experimental result shows measurements of the profile of a step object with a 4.6-mu-m synthetic wavelength.