Single-shot dispersive interferometry for inline surface inspection

The dispersive interferometry provides an instantaneous surface measurement in a single camera frame, making it resistant to environmental disturbances and ideal for in-process surface metrology. It also benefits from the extended measurement ranges in both depth and lateral directions by incorporating hyperspectral imaging technology and cylindrical beam illumination, respectively. This paper reports on an in-house developed cylindrical lens-based dispersive interferometer for high-accuracy surface inspection, particularly for structured surfaces. The obtained spectral interferogram is analyzed using the fringe order algorithm, in which the phase slope method is used to calculate the initial height to resolve the fringe order ambiguity and eventually an improved height value can be obtained using the exacted phase of a single wavelength. Experiments demonstrate that the measurement noise of the developed interferometry system is less than 1 nm within the measurement range. A brass step sample made by a diamond turning machine was measured and the experimental results closely align with those given by the commercial white light interferometer -Talysurf CCI 3000.