Our group has developed a digital holographic interferometry camera based on an off-axis dual-beam setup. A single hologram acquired with the camera represents the phase and intensity distributions of light reflecting off the surface of an object. Our goal was to develop an algorithm that converted the acquired hologram into a 3D representation of the object. First, to determine the phase excursion of the object, a discrete Fresnel transform reconstruction was applied to a high-pass-filtered version of the hologram. The reconstructed phase map contained both the spatial carrier fringes due to the off-axis geometry of our setup and the phase information related to the object’s surface. Next, we developed a reliable 2D spatial carrier fringe removal technique that was capable of separating out the object’s phase information from the carrier fringes. Last, the object phase map was calibrated to convert the phase information to height information based on the geometrical parameters of the system. The system was evaluated using a silicon-etched lateral-axial resolution target based on a USAF design. The system achieved 33 nanometer axial resolution and sub-pixel lateral resolution over a wide field of view of more than 10 mm x 10 mm. The algorithm will enable the digital holographic camera to be used for non-destructive testing of surface morphology at nanometer scales. With repeated acquisitions, the algorithm has the potential to estimate nanometer-scale dynamic vibrations of an object’s surface.
Parsa Omidi, Hui Wang, Mamadou Diop, and Jeffrey J. L. Carson, "Algorithm for phase-displacement conversion from reflection digital holographic interferometry," Proc. SPIE 10944, Practical Holography XXXIII: Displays, Materials, and Applications, 109440Q (Presented at SPIE OPTO: February 05, 2019; Published: 1 March 2019); https://doi.org/10.1117/12.2507566.
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