Aqueye Plus: a very fast single photon counter for astronomical photometry to quantum limits equipped with an Optical Vortex coronagraph

In recent years, we developed two very high speed single photon photometers, Aqueye and Iqueye, as prototypes for “quantum” photometers for the Extremely Large Telescopes of the next decade. These instruments, based on single photon avalanche photodiodes and a 4-fold split-pupil concept, have been successfully used to obtain data of the highest quality on optical pulsars. Subsequently, we performed an attempt to utilize the Orbital Angular Momentum and associated Optical Vorticity to achieve high performance stellar coronagraphy. Presently, we are making a synergic effort in building Aqueye Plus, a new instrument for the 1.8 m telescope of the Asiago - Cima Ekar Observatory, which combines both functions, namely high speed simultaneous multicolor photon counting photometry and stellar coronagraphy. The innovative capability of Aqueye Plus is to take advantage of the two parallel outputs (NIM and TTL) of the four high time accuracy photon counting sensors. The NIM output preserves the best timing capability, while the TTL output drives a deformable 32-element mirror in a sort of quadrant detector to correct for defocus and tip/tilt aberrations of the stellar image on the phase mask discontinuity. This paper describes the Aqueye Plus instrument main characteristics and its foreseen performance.