Instantaneous phase-shift Fizeau interferometer utilizing a synchronous frequency shift mechanism

An on-axis, vibration insensitive, polarization Fizeau interferometer is realized through the use of a pixelated polarization mask spatial carrier phase shifting technique in conjunction with a high coherence source and a polarization frequency shift device. In this arrangement, differential motion between the test and reference surfaces, in conjunction with the polarization frequency shift device, is used to effectively separate the orthogonally polarized test and reference beam components for interference. With both the test and the reference beams on-axis, the common path cancellation advantages of the Fizeau interferometer are maintained. Additionally, the use of a high coherence source eliminates the need to path match the test and reference arms of the interferometer. Using a 1 mW HeNe source, the optimum camera shutter speed, used when measuring a 4% reflector, was 250 usec, resulting in significantly reduced vibration sensitivity. Experimental results show the performance of this new interferometer to be within the specifications of commercial phase shifting interferometers.