Optical/IR interferometry: history and basic principles

The present notes refer to a series of lectures delivered in September 2017 in Roscoff (France) during the 2017 Evry Schatzman School, at IUCAA (Inter-University Center for Astronomy and Astrophysics, Pune, India) in April 2018, during the July-September 2020 period and during the November 2020-January 2021 period via on-line lectures organized by IUCAA and by the Astronomical Observatory Institute, Adam Mickiewicz University in Poznan, respectively.
It concerns a general introduction to optical/IR interferometry, including a brief history, a presentation of the basic principles, some important theorems and relevant applications. The layout of these lecture notes is as follows. After a short introduction, we proceed with some reminders concerning the representation of a field of electromagnetic radiation. We then present a short history of interferometry, from the first experiment of Fizeau and Stefan to modern optical interferometers. A first intuitive approach of the Zernicke-van Cittert theorem is proposed. We then discuss the notions of light coherence, including a rigorous demonstration of the theorem of Zernicke-van Cittert and describe the principle of interferometry using two telescopes. We present some examples of modern interferometers and observational results obtained with these. Finally, we address three important theorems: the fundamental theorem, the convolution theorem and the Wiener-Khinchin theorem which enable to get a better insight into the field of optical/IR interferometry. Below are links to the YouTube videos—featuring Jean Surdej, open lectures, IUCAA (Pune, India), and the University of Liège (Belgium)—as well as links to the Zoom meetings that began on July 27, 2020—including a recording of the live session between the course participants and Professor Jean Surdej.