Deflectometry encoding the measured angle in a time-dependent intensity signal

Abstract

We propose a new concept of a deflectometer, aimed to provide high accuracy measurements with high sampling rate and low noise, as required by state-of-the-art slope-measuring profilometers, like Long Trace Profilometers or Nanometer Optics Measuring instruments. For this purpose, we introduce certain modifications to the usual working principle of autocollimators so that the measured angle is not given by the displacement of the pattern captured by a CCD, but by the harmonic contents of the time-modulated intensity signal acquired by a photodiode. By doing this, the signal can be sampled not by just a few thousand pixels but by millions of samples/s.

Deflectometry for specular surfaces: an overview

“…Low-uncertainty flatness tests are usually accomplished with interferometry. Remarkably, some varieties of DM are able to improve on its performance and reach down to sub-nm uncertainty levels (Illemann et al, 2002;Pedreira et al, 2019;Siewert et al, 2019;Ehret et al, 2021). Slope maps are recorded here with a scanning autocollimator, and the surface reconstruction is based on several 1D scans.…”

Deflectometry for specular surfaces: an overview

“…Low-uncertainty flatness tests are usually accomplished with interferometry. Remarkably, some varieties of DM are able to improve on its performance and reach sub-nm uncertainty levels [53][54][55]. Slope maps are recorded here with a scanning autocollimator, and the surface reconstruction is based on several 1D scans.…”