Exploiting light coherence in astrophysics

TL;DR

This paper explores how light coherence, especially second-order coherence, can be exploited in astrophysics to gain insights into stellar emission mechanisms and distinguish between different radiation processes.

Contribution

It highlights the potential of using second-order coherence measurements as a new observational tool in astrophysics to analyze emission processes.

Findings

Second-order coherence can reveal photon statistics of sources.

Coherence measurements can differentiate emission mechanisms.

Light coherence acts as a complementary messenger in astrophysical observations.

Abstract

The Hanbury Brown-Twiss (HBT) effect, discovered in the 1950s and further developed in the 1960s, was originally used to estimate stellar angular diameters through intensity correlations measured by spatially separated detectors. Further developments started from HBT experiments to exploit quantum bunching of photons in incoherent light sources played foundational role in the development of quantum optics. When the two detectors in an HBT experiment are co-located, typically implemented using a beam splitter, a zero-baseline intensity correlation is obtained, which after deconvolution of the detector response function, yields the temporal component of the second-order coherence function. Unlike spatial correlations, this function is independent of the source brightness distribution, or its size, giving direct insight into the properties of the source's emission process itself - photon statistics. Along with photometric and spectral information, the second order coherence function can be used to constrain the emission mechanisms and discriminate between thermal, synchrotron, bremsstrahlung and stimulated emission processes. Evolution of the emission processes would likewise drive changes in the second order coherence. Light coherence information along with multi-wavelength observations, can become a complementary "messenger", carrying internal information about the astronomical source.