Comparing Optical and Radio — Quantum Issues

Abstract

Once upon a time, there were radio and optical astronomers, each group with its own way of detecting and thinking about radiation. In spite of the shock treatment administered by Hanbury-Brown and Twiss more than thirty five years ago, this dichotomy persists to a surprising extent even today. As new techniques emerge, we clearly need to do better. Coherent and incoherent detection, heterodyning and interferometry are all situations where a full analysis involves quantum behaviour of the radiation. This informal review covers the general approach needed and goes over some points of principle which arise.