Real time two color variable resolution video moire and error map moire using a Mach-Zehnder interferometer
Blatt, Joel H.
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A variable resolution two color video moire system has been built which uses a dual laser illuminated Mach-Zehnder interferometer as the fringe projector. One input of the interferometer is illuminated by a He-Ne laser and the other by an Argon-Ion laser, allowing simultaneous projection of red and green fringes with different spatial frequencies. The dual interferometer outputs are also used, allowing illumination of both the target and reference surfaces. Video cameras view the two surfaces and by mixing the video signals with a chroma-key mix in a video special effects generator, real time moire can be observed. A piezo-electrically driven mirror can be used to continuously shift the fringes while taking a video average, which eliminates the fringes in the final image and improves the signal-to noise of the moire contours. If the reference surface is a plane, the moire contours seen are equal depth contours with higher than normal resolution due to the two fringe systems. Because the moire contours or the distorted fringes in each color can be independently recovered, improved shape recovery over discontinuities is possible. By a different configuration ofthe projection optics following the interferometer, it is possible to spatially separate the red and green projected fringes and simultaneously illuminate two different shaped reference surfaces. When operated in this mode with flat plate and perfect object reference surfaces, both conventional equal depth moire and error map moire can be seen, one in each color. Applications and limitations of the system will be discussed.