Distance sensing emerging from second-order interference of thermal light

TL;DR

This paper presents a novel distance sensing technique using second-order interference of thermal light, enabling remote distance measurements even without first-order coherence, and applicable in turbulent environments.

Contribution

The authors introduce a second-order interferometric method for distance sensing with thermal light, revealing new critical parameters and interference phenomena.

Findings

Distance can be estimated via second-order correlations even without first-order coherence.

The method works in turbulent conditions, measuring remote object distances.

New parameters characterize the degree of second-order correlation and interference emergence.

Abstract

We introduce and describe a technique for distance sensing, based on second-order interferometry of thermal light. The method is based on measuring correlation between intensity fluctuations on two detectors, and provides estimates of the distances separating a remote mask from the source and the detector, even when such information cannot be retrieved by first-order intensity measurements. We show how the sensitivity to such distances is intimately connected to the degree of correlation of the measured interference pattern in different experimental scenarios and independently of the spectral properties of light. Remarkably, this protocol can be also used to measure the distance of remote reflective objects in the presence of turbulence. We demonstrate the emergence of new critical parameters which benchmark the degree of second-order correlation, describing the counterintuitive emergence of spatial second-order interference not only in the absence of (first-order) coherence at both detectors but also when first order interference is observed at one of the two detectors.