Intensity interferometry: Optical imaging with kilometer baselines

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.

12 pages, 3 figures, 92 references. Invited keynote talk presented at the conference 'SPIE Astronomical Telescopes + Instrumentation', Edinburgh, Scotland (2016); to be published in SPIE Proc. 9907, 'Optical and Infrared Interferometry and Imaging V'