Polarization wavefront shaping for quantitative phase contrast imaging by axially-offset differential interference contrast (ADIC) microscopy

Abstract

Axially-offset differential interference contrast (ADIC) microscopy was developed for quantitative phase contrast imaging (QPI) by using polarization wavefront shaping approach with a matched pair of micro-retarder arrays. In ADIC microscopy, wavefront shaping with a micro-retarder array (μRA) produces a pattern of half-wave retardance varying spatially in the azimuthal orientation of the fast-axis. For a linearly polarized input beam, the polarization pattern induced from the linearly polarized plane wave through the μRA is identical to the interference between a slightly diverging right circularly polarized (RCP) and a slightly converging left circularly polarized (LCP) plane wave. Using a 10× objective, two axially offset foci separated by 70 μm are consequently generated from the patterned wavefront with orthogonal polarization states, serving as the sample and reference focal planes respectively for QPI. A paired μRA in transmission coherently recombines the two orthogonal components to recover the incident polarization state in the absence of sample. The large spatial offset (roughly 1/10 of the field of view) between the two foci provides a stable and uniform reference. Quantitative phase contrast images are directly recovered from sample-scan measurements with a single-channel detector and lock-in amplification with fast polarization modulation. This method has been successfully used for bio-sample imaging, nanoparticle detection and refractive index calculation of silica microbeads.