Multipass wide-field phase imager

TL;DR

This paper introduces a versatile wide-field phase imaging method that uses a non-resonant cavity and a single-photon camera to achieve sub-nanometer resolution over large areas, with enhanced sensitivity and low-light performance.

Contribution

The work presents a novel multipass interference contrast imaging technique combining a self-imaging cavity and time-of-flight single-photon detection for improved phase measurement sensitivity.

Findings

Over four-fold reduction in phase measurement noise.

Achieves sub-nm sample-thickness resolution over several mm².

Close to theoretical sensitivity limits with ideal cavity configurations.

Abstract

Advances in optical imaging always look for an increase in sensitivity and resolution among other practicability aspects. Within the same scope, in this work we report a versatile interference contrast imaging technique, capable of sub-nm sample-thickness resolution, with a large field-ofview of several mm2. Sensitivity is increased through the use of a self-imaging non-resonant cavity, which causes photons to probe the sample in multiple rounds before being detected, where the configuration can be transmissive or reflective. Phase profiles can be resolved individually for each round thanks to a specially designed single-photon camera with time-of-flight capabilities and true pixels-off gating. Measurement noise is reduced by novel data processing combining the retrieved sample profiles from multiple rounds. Our protocol is specially useful under extremely low light conditions as require by biological or photo-sensitive samples. Results demonstrate more than a four-fold reduction in phase measurement noise, compared to single round imaging, and close valuesto the predicted sensitivity in case of the best possible cavity configuration, where all photons are maintained until n rounds. We also find a good agreement with the theoretical predictions for low number of rounds, where experimental imperfections would place a minor role. The absence of a laser or cavity lock-in mechanism makes the technique an easy to use inspection tool.