White light diffraction phase microscopy with slightly off-axis blind two-step phase-shifting

Abstract

White light diffraction phase microscopy (wDPM) combines many of the best attributes of current quantitative phase imaging (QPI) techniques, which fully takes advantages of both high temporal and spatial phase sensitivity granted by the common-path geometry and the white light illumination. However, like all off-axis quantitative phase imaging methods, although wDPM benefits from the acquisition rate due to the single shot measurement, it is characterized by a reduced space–bandwidth product, compared to phase shifting approaches. In the paper, we develop slightly off-axis blind two-step phase-shifting wDPM, measuring two phase-shifted interferograms by blindly shifting the grating. Due to the combination of phase-shifting and off-axis techniques, the time–bandwidth and space–bandwidth products are well traded off. In addition, the phase-shifting is simply implemented by blindly shifting the grating with a stepping motor linear translation stage, not requiring a precise phase modulator. Thus, the apparatus is cost-effective and offers ease of alignment. Some experimental results are given to demonstrate the feasibility of the method.