High resolution shape measurements with Phase-Shifting Schlieren (PSS)

摘要

A new technique to measure shapes and deformation with a high resolution is proposed. It combines the conventional Schlieren technique principle with the phase-shifting approach generally used in interferometry. By an adequate Schlieren filter and an adapted set-up, some Schlieren Fringes are generated. After the application of the phase shift technique, the Schlieren phase is calculated and converted into beam deviation values, which are integrated to deduce the object's shape. Both theoretical and experimental demonstrations are given. The technique is first validated on a reference target. With a setup working in reflection, we have measured the curvature radius of a lens surface with accuracy better than 1%. Then an application in a fluid physics experiment is given. The shape of a liquid-gas interface in a conventional Marangoni-Benard experiment has been measured with a resolution of 30nm and amplitudes up to 50 μm. The shape of MEMS has also been measured in a PSS microscope with a nanometric resolution. Finally, we propose an adaptation of the setup to make it possible the measurement of fast phenomena at video frame rate.