Optical interferometers for surface metrology require high immunity to vibration when they are to be used outside the laboratory environment. Here we describe a continuous phase-shifting method as a means of vibration suppression, which implements phase shifting uninterruptedly while capturing resulting interference fringes at a high rate. The continuous phase shifting allows the interference initial phase under measurement to be locked to a single temporal frequency in captured fringes, thereby being recovered free from vibration by Fourier-based postprocessing. This continuous phase-shifting method can be realized with any phase-shifting interferometers by incorporating a high-speed digital camera with good intensity-to-voltage conversion linearity.
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