Intensity interferometry: Optical imaging with kilometer baselines

TL;DR

This paper reviews intensity interferometry, a technique enabling optical imaging with kilometer-scale baselines by electronically connecting telescopes, which overcomes atmospheric turbulence issues and is now feasible with Cherenkov telescope arrays.

Contribution

It provides a comprehensive overview of intensity interferometry, from its origins to recent experimental demonstrations and future prospects for high-resolution optical imaging.

Findings

Digital intensity interferometry has successfully reconstructed diffraction-limited images.

Arrays of Cherenkov telescopes can achieve kilometer-scale baselines for optical imaging.

The technique circumvents atmospheric turbulence issues inherent in traditional methods.

Abstract

Optical imaging with microarcsecond resolution will reveal details across and outside stellar surfaces but requires kilometer-scale interferometers, challenging to realize either on the ground or in space. Intensity interferometry, electronically connecting independent telescopes, has a noise budget that relates to the electronic time resolution, circumventing issues of atmospheric turbulence. Extents up to a few km are becoming realistic with arrays of optical air Cherenkov telescopes (primarily erected for gamma-ray studies), enabling an optical equivalent of radio interferometer arrays. Pioneered by Hanbury Brown and Twiss, digital versions of the technique have now been demonstrated, reconstructing diffraction-limited images from laboratory measurements over hundreds of optical baselines. This review outlines the method from its beginnings, describes current experiments, and sketches prospects for future observations.