A Micromechanical Actuator With Capacitive Position Correction for Phase Shifting Diffraction Interferometry

An electrostatically-actuated micro phase shifter with capacitive position feedback for linearization is presented in this paper. The travel range of the micro phase shifter is 1.2 μm, and a lock-in amplifier capacitive sensing circuit capable of 1.5 nm position accuracy is developed and with a digital signal processor generates a position feedback correction curve to achieve a linearized travel trajectory. The eventual application for this microactuator is to provide linear phase shifting in the phase shifting diffraction interferometer (PSDI) developed at LLNL Which can perform optical metrology down to 2Å accuracy.