Displacement measurement in a Sagnac interferometer with thermal light second-order correlation

We report a displacement measurement experiment in second-order correlation and subwavelength correlation with thermal light. Our target is a single slit, which is inserted into a Sagnac interferometer to mimic a double-slit apparatus. According to the correlated diffraction pattern, we can predict the excursion of the slit from the optical axis. When the slit is shifted, we can predict the displacement accurately. We also present the mathematical presentations of beam propagation and reflection in comprehensive deduction.