Near-infrared lensless holographic microscopy on a visible sensor enables label-free high-throughput imaging in strong scattering

TL;DR

This paper introduces near-infrared lensless holographic microscopy using visible sensors, enabling high-throughput, label-free imaging of strongly scattering biological tissues with improved resolution and depth penetration.

Contribution

It demonstrates the feasibility of NIR-LDHM on standard visible sensors, extending lensless holography into strongly scattering regimes with minimal hardware modifications.

Findings

NIR-LDHM maintains resolution through scattering layers up to 1.4 mm.

Resolution improves twofold with increased sample-sensor distance.

Successful label-free imaging of mouse tissue slices up to 250 um deep.

Abstract

Lensless digital holographic microscopy (LDHM) relies on interference between an unscattered reference wave and a weakly scattered object wave - an assumption that rapidly fails in turbid samples under multiple scattering. To overcome this limitation, we present near-infrared LDHM (NIR-LDHM), a in-line holographic platform that operates up to the silicon cutoff (~1100 nm) using a conventional board-level CMOS sensor designed for visible (VIS) imaging. Using tissue-mimicking milk scattering layers and calibrated resolution targets, we quantify reconstruction performance versus wavelength, scattering strength, and sample-sensor distance. NIR-LDHM maintains resolvable features through scattering layers up to ~1.4 mm, whereas visible regime fails to resolve features below ~350 um. Importantly, despite a detector quantum efficiency of only 0.19% at 1100 nm, robust reconstructions are obtained under low-photon-budget conditions. We further identify advantageous mechanism by which increasing the sample-sensor distance from ~3 to 12 mm improves lateral resolution by twofold under strong scattering. Finally, we demonstrate wide-field, label-free amplitude-phase imaging of uncleared mouse tissues, resolving internal structure in brain and liver slices up to ~250 um and ~60 um, respectively. By extending lensless complex-field microscopy into strongly scattering regimes with minimal hardware changes, this work has relevance to computational imaging through complex media and biophotonics.