Shape measurement by multi-illumination method in digital holographic interferometry

In this paper, temporal phase unwrapping and short time Fourier transform (STFT) are proposed for shape measurement of an object with height steps by digital holographic interferometry (DHI). A series of digital holograms is recorded with a high-speed CCD camera using a multi-illumination method. Each pixel is processed along the time axis independently of other pixels. Two novel methods are proposed to process the wrapped phase maps: the first method is based on complex phasor (CP) and temporal phase unwrapping, and the second method is based on CP and STFT. In the STFT method, continuous phase maps are obtained by integration of the exacted instantaneous frequency. The continuous phase map can characterize the profile of the object with height steps. An experiment is conducted to verify the validity of the proposed methods.