Multiple-Wavelength and Multiple-Source Holography Applied to Contour Generation*

This paper describes two methods for obtaining three-dimensional holographic images containing superimposed constant-range contours for accurate cross-section tracing or contour mapping. The first and simplest method requires two illuminating sources with identical wavelength but at slightly different positions. This method has the drawback of requiring the hologram to be made at right-angles to the illumination direction. This results in shadowed areas on the object. The second method requires an illuminating source containing two wavelengths. This method also requires precise positioning of two reference sources, one for each wavelength. The positions of the reference sources may be optimized so that contours will appear over a maximum object angle. Experimental results that prove the principle are shown.