Coherence-encoded synthetic aperture for super-resolution quantitative phase imaging

Abstract

Quantitative phase imaging (QPI) has quickly established its role in identifying rare events and screening in biomedicine or automated image data analysis using artificial intelligence. These and many other applications share the requirement for extensive high-quality datasets, which is challenging to meet because the invariance of the space–bandwidth product (SBP) fundamentally limits the microscope system throughput. Here, we present a method to overcome the SBP limit by achieving QPI super-resolution using a synthetic aperture approach in a holographic microscope with a partially coherent broad source illumination. We exploit intrinsic coherence-gating properties of the partially coherent light combined with the oblique illumination provided by the diffraction on a simple phase grating placed in proximity of the specimen. We sequentially coherence gate the light scattered into each grating’s diffraction order, and we use the acquired images to synthesize QPI with significantly increased spatial frequency bandwidth. The resolution of QPI is increased substantially beyond Abbe’s diffraction limit while a large field of view of low numerical aperture objectives is kept. This paper presents a thorough theoretical treatment of the coherence-gated imaging process supplemented by a detailed measurement methodology. The capability of the proposed method is demonstrated by imaging a phase resolution target and biological specimens. We envision our work providing an easily implementable super-resolution QPI method particularly suitable for high-throughput biomedical applications.