Abstract
Conventional low-magnification phase-contrast microscopy is an invaluable, yet a qualitative, imaging tool for the interrogation of transparent objects over a mesoscopic millimeter-scale field-of-view in physical and biological settings. Here, we demonstrate that introducing a compact, unbalanced phase-shifting Michelson interferometer into a standard reflected brightfield microscope equipped with low-power infinity-corrected objectives and white light illumination forms a phase mesoscope that retrieves remotely and quantitatively the reflection phase distribution of thin, transparent, and weakly scattering samples with high temporal (1.38 nm) and spatial (0.87 nm) axial-displacement sensitivity and micrometer lateral resolution (2.3 μm) across a mesoscopic field-of-view (2.25 × 1.19 mm2). Using the system, we evaluate the etch-depth uniformity of a large-area nanometer-thick glass grating and show quantitative mesoscopic maps of the optical thickness of human cancer cells without any area scanning. Furthermore, we provide proof-of-principle of the utility of the system for the quantitative monitoring of fluid dynamics within a wide region.
Highlights
Wide-field quantitative phase imaging based on near-common-path off-axis interferometry has lately been demonstrated to visualize the topography of millimeter-sized reflective and transmissive samples with nanometer axial-displacement sensitivity across impressively large FOVs of up to ~232 mm[2], but with lateral resolution of several tens of micrometers[21,22]
We introduce a technique termed quantitative phase mesoscopy (QPMES) that enables the visualization of the reflection phase distribution of thin, label-free, optically transparent and weakly scattering specimens at micrometer resolution over a mesoscopic FOV with no area scanning and with nanometer spatiotemporal sensitivity to optical path-length changes
We have presented quantitative phase mesoscopy (QPMES) that employs remote coherence tuning of phase-shift interference patterns to enable mapping of the reflection phase distribution of thin, label-free, optically transparent, and weakly scattering samples with micrometer lateral resolution and nanometer spatiotemporal axial-displacement sensitivity across a mesoscopic area
Summary
Wide-field quantitative phase imaging based on near-common-path off-axis interferometry has lately been demonstrated to visualize the topography of millimeter-sized reflective and transmissive samples with nanometer axial-displacement sensitivity across impressively large FOVs of up to ~232 mm[2], but with lateral resolution of several tens of micrometers[21,22]. In recent years, novel lensless on-chip imaging modalities based on digital inline holography have been developed to obtain phase-contrast imaging with high sub-micron resolution over a wide FOV (~24–30 mm2)[29,30] These modalities provide better visualization of transparent, weakly scattering objects with simple instrumentation (but involved mathematical processing), it still remains to assess their stability against phase noise, and quantify their measurement sensitivity to minute optical path-length changes. Unlike large-area phase imaging based on off-axis Mach-Zehnder interferometric systems and custom-built lensless on-chip digital inline holographic modalities, QPMES provides a novel and simple means for retrofitting most existing reflected brightfield microscopes into quantitative phase imagers with no need for area scanning using a single compact Michelson interferometer This retrofitting can be realized in various topologies, here we incorporate a near-common-path phase-shifting Michelson interferometer into the infinity-corrected path of a home-built brightfield microscope equipped with white light epi-illumination and low power objectives. We provide proof-of-principle of the utility of the system for the quantitative monitoring of fluid dynamics within a large area
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