Dynamic Fizeau interferometer with assistant defocused source

We report and demonstrate a dynamic Fizeau interferometer (DFI) capable of high-precision measurements under severe vibration. The method involves two interferometric passes: a null-interference pass (NP) and a circular carrier-frequency pass (CP). The NP adopts an on-axis Fizeau design, preserving the common path of the reference and test beams. The CP uses an assistant defocused source to generate circular fringe patterns, assisting the NP in phase extraction and sign correction. The feasibility and performance of the proposed method are demonstrated experimentally. To the best of our knowledge, this is the first proposal of a general asynchronous phase-shifting DFI that can not only demodulate null-fringe patterns and correct phase-sign ambiguity but can also maintain the common-path advantages of the Fizeau interferometer.