Direct illumination calibration of telescopes at the quantum precision limit

TL;DR

This paper demonstrates that telescope calibration using direct illumination can reach quantum-limited precision, with photon statistics as the fundamental limit, and introduces a model incorporating diffuse light effects for enhanced accuracy.

Contribution

It presents a novel calibration method achieving near quantum-limited precision and models diffuse light interference to improve optical surface monitoring.

Findings

Photon statistical fluctuation limits calibration precision below 1 ppm.

Diffuse light effects can be characterized with 10 ppm accuracy.

Spatial frequency analysis constrains optical surface roughness.

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 interferes 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.