Imaging below the camera noise floor with a homodyne microscope

TL;DR

This paper introduces a homodyne microscopy technique that captures both intensity and phase images in extremely low-light conditions, surpassing the camera's noise floor by interference with a bright reference beam.

Contribution

The authors demonstrate a novel wide-field homodyne imaging system capable of recovering images below the camera's noise floor using a single frame and interference, enabling low-light imaging in challenging conditions.

Findings

Imaging down to 1.1 photons per pixel per frame

Achieved a 29.2% reduction in resolution

Operated with a 300,000:1 reference to probe beam ratio

Abstract

We present a wide-field homodyne imaging system capable of recovering intensity and phase images of an object from a single camera frame at an illumination intensity significantly below the noise floor of the camera. By interfering a weak imaging signal with a much brighter reference beam we are able to image objects in the short-wave infrared down to signal intensity of $\sim$$1.1$ photons per pixel per frame incident on the sensor despite the camera having a noise floor of $\sim$$200$ photons per pixel. At this illumination level we operate under the conditions of a reference beam to probe beam power ratio of $\sim$$300$,$000$:$1$. There is a corresponding $29.2\%$ drop in resolution of the image due to the method implemented. For transmissive objects, in addition to intensity, the approach also images the phase profile of the object. We believe our demonstration could open the way to low-light imaging in domains where low noise cameras are not available, thus vastly extending the range of application for low-light imaging.