Single-photon super-resolved spectroscopy from spatial-mode demultiplexing

TL;DR

This paper introduces a novel super-resolution spectroscopy method using spatial-mode demultiplexing to analyze incoherent light sources below the diffraction limit, enabling better spectral separation of overlapping sources.

Contribution

It extends spatial demultiplexing techniques from imaging to spectroscopy, demonstrating super-resolution spectral analysis of closely spaced incoherent sources.

Findings

Successfully distinguished spectra of sources below diffraction limit

Demonstrated effective separation of overlapping sources

Proposed application for exoplanet atmosphere studies

Abstract

We demonstrate spectroscopy of incoherent light with sub-diffraction resolution. In a proof-of-principle experiment we analyze the spectrum of a pair of incoherent point-like sources whose separation is below the diffraction limit. The two sources mimic a planetary system, with a brighter source for the star and a dimmer one for the planet. Acquiring spectral information about the secondary source is hard because the two images have a substantial overlap. This limitation is solved by leveraging a structured measurement based on spatial-mode demultiplexing, where light is first sorted in its Hermite-Gaussian components in the transverse field, then measured by photon detection. This allows us to effectively decouple the photons coming from the two sources. An application is suggested to enhance exoplanets' atmosphere spectroscopy. A number of experiments of super-resolution imaging based on spatial demultiplexing have been conducted in the past few years, with promising results. Here, for the first time to the best of our knowledge, we extend this concept to the domain of spectroscopy.