Nanometer resolution of three-dimensional motions using video interference microscopy

An interferometric video system for measuring microelectromechanical systems (MEMS) with nanometer resolution is demonstrated. Interferograms are generated by combining light reflected from the target with light reflected from a reference mirror. Motions are determined from sequences of stop-action interferograms obtained with stroboscopic illumination. The system was used to measure motions of a microfabricated accelerometer. In-plane motions were determined by analysis of brightfield images using gradient methods with subpixel resolution. Results are compared for brightfield images obtained by blocking light from the reference arm of the interferometer and for brightfield images reconstructed from interferograms. Out-of-plane motions are determined by analyzing interferograms obtained with different positions of the reference mirror. Results demonstrate nanometer resolution of in-plane motions and subnanometer resolution of out-of-plane motions.