Efficient optomechanical mode-shape mapping of micromechanical devices

Visualizing eigenmodes is crucial in understanding the behavior of state-of-the-art microme-chanical devices. We demonstrate a method to optically map multiple modes of mechanical structures simultaneously. The fast and robust method, based on a modified phase-lock loop, is demonstrated on a silicon nitride membrane and shown to outperform three alternative approaches. Line traces and two-dimensional maps of different modes are acquired. The high quality data enables us to determine the weights of individual contributions in superpositions of degenerate modes.