Compact dual-wavelength off-axis digital holography for quantitative phase imaging

Abstract

Off-axis dual-wavelength digital holography (oaDWDH) can enable quantitative phase imaging on thickness samples without numerical phase unwrapping in a single shot. However, the traditional oaDWDH is huge and unstable owing to its separated-path geometries. In this paper, we presented a compact oaDWDH using wavefront-splitting in the quasi common-path. In our approach, a dual-wavelength spherical wave is split into two parts to act as the reference wave and the object wave, respectively. Only a few such optical elements as a mirror and a beam splitter are employed to adjust and recombine the two waves, and a hologram containing two-wavelength information is then captured by a monochromatic CCD camera. The information of a specimen, including phase and height, can be reconstructed through a division algorithm with the help of a specimen-free multiplexed interferogram. In order to verify the feasibility of the system, observations were performed on the step samples. The height of the sample is obtained quantitatively, and finally compared with the measured height result of the step sample by AFM to prove the accuracy of the measurement result.