Performance and testing of a four channel high-resolution heterodyne interferometer

When studying complex vibrations, simultaneous measurements at several points are indispensable if one is dealing with objects whose vibrational behavior is not guaranteed to be stable over longer periods of time, such as biological specimens, micro-mechanical elements or objects characterized by nearly resonant normal modes with different vibrational patterns. Obviously, both amplitude and phase need to be measured at each point to obtain a full characterization of the vibration. We introduce birefringent beam displacers as a highly efficient beam multiplying method to create a system of four heterodyne interferometers operating in parallel from a single laser source. The design and the performance characteristics (resolution, cross-talk) of the instrument will be discussed. The system revealed the existence of running vibrational modes on an electrically driven plate clamped along its outer edge. (C) 2008 Elsevier Ltd. All rights reserved.