Three wavelengths parallel phase-shift interferometry for real-time focus tracking and vibration measurement

Instantaneous high-resolution, wide-range focus tracking and a vibrometry system based on three-wavelength (3λ) parallel phase-shift polarization interferometry using three detectors per wavelength is presented. The system, implementing 3λ in-parallel three-phase-shift-interferometry channels for the first time, to the best of our knowledge, allows single-shot position tracking of motion profiles with extremely high velocities and vibration rates, long inter-step heights, and sub-nanometer scale accuracy. The system's simple design and algorithm presented here do not rely on active optical components, making its performance limited only by the detectors' bandwidths and allowing the setting up of a very high-performance low-cost vibrometry system.