Three-dimensional shape measurement based on dual-refractive-index digital holography

A novel phase-imaging method based on dual-refractive-index digital holography has been presented, which in principle can be arbitrarily large compared to the wavelength and does not involve the usual phase unwrapping by detection of phase discontinuity. The method consists of the generation and combination of two phase maps in a digital holography system by use of two separate refractive indexes which varies with the air density in an air chamber where a recorded 3D object is in. For example, we have reconstructed the surface of a remote control keypad of size 5 mm×5 mm and maximum axial depth 0.631 mm, and the experimental result shows that the proposed approach is feasible and effective.