Characterization of very narrow spectral lines with temporal intensity interferometry

TL;DR

This paper demonstrates that temporal intensity interferometry can resolve extremely narrow spectral lines in starlight, surpassing traditional spectrograph resolution limits by analyzing photon arrival times.

Contribution

It introduces a novel method combining spectral filtering with single-photon temporal correlation to measure linewidths in the time domain, enabling detection of very narrow spectral features.

Findings

Resolved a 20 MHz linewidth in laboratory laser light

Identified coherent laser contribution within blackbody radiation

Surpassed conventional spectrograph resolution limits

Abstract

Context: Some stellar objects exhibit very narrow spectral lines in the visible range additional to their blackbody radiation. Natural lasing has been suggested as a mechanism to explain narrow lines in Wolf-Rayet stars. However, the spectral resolution of conventional astronomical spectrographs is still about two orders of magnitude too low to test this hypothesis. Aims: We want to resolve the linewidth of narrow spectral emissions in starlight. Methods: A combination of spectral filtering with single-photon-level temporal correlation measurements breaks the resolution limit of wavelength-dispersing spectrographs by moving the linewidth measurement into the time domain. Results: We demonstrate in a laboratory experiment that temporal intensity interferometry can determine a 20 MHz wide linewidth of Doppler-broadened laser light, and identify a coherent laser light contribution in a blackbody radiation background.