Digital holographic metrology based on multi-angle interferometry.

We propose a multi-angle interferometry method for digital holographic metrology. In an application of three-dimensional (3D) reconstruction, the hologram corresponding to a different illumination angle is recorded as the illumination angle with a single wavelength tilted at regular intervals by an electronically controlled rotating stage. A Fourier-transform-based axial depth scanning algorithm formed by the reconstructed phase is used to obtain the height point by point over the whole field of view. Hence, the 3D reconstruction can be obtained effectively; even the object has large depth discontinuities resulting from the difficulty of the phase unwrapping. Due to a monochrome source only being used, the method is available for objects with wavelength-dependent reflectivity and those that are free of chromatic aberration caused by the different wavelengths.