Very fast photon counting photometers for astronomical applications: IquEYE for the ESO 3.5m New Technology Telescope

Abstract

ABSTRACT Almost all astronomical instruments detect and analyze the “rst order spatial and/or temporal coherence prop-erties of the photon stream coming from celestial sources. Additional information might be hidden in the secondand higher order coherence terms, as shown long ago by Hanbury-Brown and Twiss with the Narrabri IntensityInterferometer. 1 The future Extremely Large Telescopes and in particular the 42 m telescope of the EuropeanSouthern Observatory (ESO) could provide the high photon ”ux needed to extract this additional information.To put these expectations (which we had already developed at the conceptual level in the QuantEYE study for the100 m OverWhelmingly Large Telescope 2,6 to experimental test in the real astronomical environment, we realizeda small prototype (Aqueye) for the Asiago 182 cm telescope. 10 This instrument is the fastest photon countingphotometer ever built. It has 4 parallel channels operating simultaneously, feeding 4 Single Photon-AvalancheDiodes (SPADs), with the ability to push the time tagging capabilities below the nano-second region for hoursof continuous operation. Aqueye has been extensively used to acquire photons from a variety of variable stars,in particular from the pulsar in the Crab Nebula. Following this successful realization, a larger version, namedIqueye, has been built for the 3.5 m New Technology Telescope (NTT) of ESO. Iqueye follows the same opticalsolution of dividing the telescope pupil in 4 sub-pupils, imaged on new generation SPADs having useful diametersof 100 micrometers, time jitter less than 50 picoseconds and dark-count noise less than 50 counts/second. Thespectral eciency of the system peaks in the visible region of the spectrum. Iqueye operated very successfully atthe NTT in January 2009. The present paper describes the main features of the two photometers and presentsome of the astronomical results already obtained.Keywords: high-speed photometry, extremely-large telescope, quantum optics, photon-avalanche diodes