Sub-micron profilometry on macroscopic free-form surfaces

An important application of deflectometry is the measurement of local (3D) surface details (e.g. scratches or milling grooves) that are only a few nanometers deep. However, these details are only visible if they can be separated from the global height variation: some objects may have a dynamic range of 1,000,000:1 or more. We present a new method for fast, quantative reconstruction of height profiles from deflectometric data. The method relies on the evaluation of curvature maps, where small details are easily detectable. After subtracting the bias curvature the profile is reconstructed by numerical integration. The accuracy of the height profile only depends on the uncertainty and the lateral resolution of the sensor. We achieve an accuracy of 10-50 nm on a measuring field of 70 mm, which we will demonstrate by several mesurements.