Direct illumination calibration of telescopes at the quantum precision limit

LPNHE, CNRS-IN2P3 and Universités Paris 6 and 7, 4 place Jussieu, 75252 Paris Cedex 05, France
e-mail: barrelet@lpnhe.in2p3.fr

Received: 12 February 2016
Accepted: 3 July 2016

Abstract

The electronic response of a telescope under direct illumination by a point-like light source is based on photon counting. With the data obtained using the SNDICE light source and the Megacam camera on the CFHT telescope, we show that the ultimate precision is only limited by the photon statistical fluctuation, which is below 1 ppm. A key feature of the analysis is the incorporation of diffuse light that interfers with specularly reflected light in the transmission model to explain the observed diffraction patterns. The effect of diffuse light, usually hidden conveniently in the Strehl ratio for an object at infinity, is characterized with a precision of 10 ppm. In particular, the spatial frequency representation provides some strong physical constraints and a practical monitoring of the roughness of various optical surfaces.