Novel solution for digital holographic interferometer design

Abstract

Digital holographic interferometry (DHI) provides full-field, non-invasive access to object and allows high sensitivity and accuracy of measurement of interference phase with high spatial resolution. Nowadays CCD and CMOS detectors and microlasers allow building miniaturized and compact digital holographic interferometers. In the paper a modular DHI system consisting of opto-electro-mechanical head and digital processing/analysis module is proposed. In order to achieve compactness and insensitivity to vibration a novel solution of interferometer head which employs two diffraction gratings is analyzed. Microlaser illuminates the first grating which acts as reference and object illumination beams generator. The first minus and plus diffraction orders form adequately reference and object beam. The second grating serves as reference and object beam recombiner providing interference pattern at the CCD matrix plane. To get off axis configuration the spatial frequencies of both gratings should differ slightly. The phase shifting version of DHI may be introduced by moving the second grating in the direction perpendicular to its lines. The usefulness of this design is proven by exemplary 3D object reconstruction and out-of-plane displacement measurement of an active silicon membrane.