Accurate dynamic phase measurement of transparent objects by the spatiotemporal phase-shifting method with polarized sensor

Measurement of density change and refractive index of transparent objects dynamically is critical in physics and engineering. In this study, a high-precision Mach-Zehnder interferometer system is developed to record the interferometric fringe of moving transparent objects with four polarization states in a single-shot using a state-of-the-art high-resolution polarization imaging camera. The phase and phase gradient distributions can be determined with extremely high accuracy, for the first time, by applying the spatiotemporal phase-shifting method (ST-PSM) developed by the authors. The ST-PSM is resistant to camera random noise and is not affected by changes in amplitude intensity or higher frequency disturbances. The absence of periodic error allows for the measurement of small changes in phase gradients that are not possible with conventional analysis. A dynamic analysis of the series of air density variations, including the plume, laminar and turbulent flows generated during gas injection from a nozzle was demonstrated. This method is also expected to be applied to bio-imaging, which measures the refractive index distribution of cells and the inspection of transparent materials by measuring the thickness distribution and stress concentration.