Mirau-type coherence scanning interferometer with integrated vibration compensation

Abstract

Coherence scanning interferometry (CSI) is a widespread optical measurement principle for inspection of surface topographies with height resolution down to the nanometer range. However, the corresponding depth scan procedure is sensitive to environmental disturbances. Thus, a highly controlled environment is required and close-to-machine or in-situ applications suffer from higher uncertainty or even failure of the measurement. Several vibration compensation approaches for CSI were introduced in the past decades. These can be mainly divided into active and passive techniques. However, no approach is known so far that compensates such environmental disturbances sufficiently. Thus, precise out of lab measurements are usually not possible. We present a Mirautype CSI system with vibration compensation, where vibrations in the longitudinal direction are detected by an interferometric distance sensor (IDS) integrated into the CSI setup. The interference images of the CSI are then rearranged according the distance values detected by the IDS. This enables a compensation of disturbances and further, precise measurements in close-to-machine environments as we show by measurements obtained in a mechanical shop floor. Furthermore, we demonstrate that a compensation of vibrations with frequencies up to 300 Hz and an amplitude of 2.45 µm is possible with our measurement setup.