Single-shot low coherence pointwise measuring interferometer with potential for in-line inspection

Abstract

Low-coherence-interferometry (LCI) is a well-known optical metrology technique which offers high resolution and a low measurement uncertainty. For the inspection of dynamic and fast processes, single-shot point sensors can show their full capability. Therefore, a new approach of an interferometer is presented, allowing an single-shot acquisition of a LCI signal. The presented concept is based on tilted wavefronts to generate a spatial modulated interferogram. Using a three faceted mirror (TFM) in the reference path, a virtual field point is generated leading to a tilted planar reference wavefront in the pupil plane of the telecentric objective lens. Three mirror surfaces, which are diamond milled out of a monolithic copper cube, are applied to guarantee a stable TFM geometry, resulting in an invariant reference field point position.