One-shot line-profiling white light interferometer with spatial phase shift for measuring rough surfaces

Abstract

White light interferometry is a promising tool for industrial quality inspection. Since modern cameras offer a frame rate far above video-rate, the speed of these systems could be increased in order to fulfill the strong temporal constraints of inline inspection, i.e. the monitoring of every single part during the production process in just a few seconds. Its accuracy up to the sub-μm range enables even the detection of smallest defects like holes with a diameter of only a few microns and thus ensures a fast, contactless and high precision quality inspection. Due to the replacement of the mechanical phase shifting by a spatial phase shift, the commonly known white light interferometers could be extended to a one-shot line-profiling sensor. The main benefit of such a line-profiling technique is that also critical surfaces are accessible that deviate strongly from a plane shape, like rotary welds on cylindrical parts. It can be shown that the accuracy of the proposed system is comparable to the accuracy of conventional white light interferometers even on rough surfaces. Other parameters like lateral resolution and measuring range strongly depend on the optical setup and will be discussed in the following sections.