Double-pass point diffraction interferometer

We propose a new point diffraction interferometer for qualitative optical analysis. Point diffraction is made two times to generate interfering waves with a single pinholed polarizer. Diffraction from a pinholed polarizer makes reference and measurement waves with a double-pass configuration. A quarter-wave plate rotates their polarization angles after reciprocation. The interferogram between the diffracted-undiffracted measurement wave and the undiffracted-diffracted reference wave is vibration-insensitive due to a common-path configuration. We examined its capability by changing the pinhole size and divergence angle of the diffracted wave for test optics with various numerical apertures.