Surface profilometry by linear scanning multi-angle digital holography.

A new, to the best of our knowledge, method named linear scanning multi-angle digital holography (LSMAX) is presented for holographic surface profilometry of object surfaces with indefinite length. A diverging cone of light illuminates the object, which is then linearly translated across the illumination, so that each object point undergoes a range of varying illumination angles, leading to a range of varying effective wavelengths. The stack of holograms thus acquired is processed using the cumulative optical phase unwrapping (COPU) principle, which builds up phase difference terms over small enough angular steps, each of these terms never exceeding 2π, so that the resultant accumulated phase can be many times 2π while maintaining the phase noise to a small fraction of 2π. Results of proof-of-principle experiments for LSMAX are presented, as well as for angle-scanning COPU of a stationary object. The same data set for LSMAX is also seen to be applicable for synthesized low-coherence topography by digital interference holography (DIH).