We have designed Aqueye+, an instrument for the Copernicus 182 cm Asiago Telescope, with two channels, one devoted to ultrafast photometry based on four single photon avalanche photodiodes, the second dedicated to stellar coronagraphy based on innovative optical vortex coronagraph system. The OVC requires a very good image quality, therefore an adaptive optic system AO was designed for the instrument. The peculiarity of this AO system is that there is no wavefront sensors, but the feedback for the deformable mirror is instead given by the photometric channel of Aqueye+.
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.
The study of the free-space propagation of quantum correlations is necessary for any future application of
quantum communication aiming to connect two remote locations. Here we study the propagation of a coherent
laser beam over over 144 Km (between Tenerife and La Palma Islands of the Canary archipelagos). By attenuating
the beam we also studied the propagation at the single photon level. We investigated the statistic of arrival of
the incoming photons and the scintillation of the beam.
In this paper is described a "push-pull" deformable mirror which has the advantage that the mirror membrane can either be attracted from the back or from the front giving several advantages such as: doubled dynamic, better accuracy in mode reproduction, and bidirectional deformation. The key idea when developing this push-pull deformable mirror was to have good compromise between performances and practical applicability for series production. An analysis of the constraints/practical limitations is described using simulations and laboratory tests. Following the results, we forsee the benefits of inserting the push-pull DM (Saturn, Adaptica Srl) in practical applications such as ophthalmology and microscopy.
In the perspective of the long range single-photon communications, we study in this work the propagation of
a single or twin optical beams in scale length of several tens to a few hundreds kilometres, introducing in the
experiment the collection of the whole beam combined to the measure of local irradiance. The experimental
models were realized in different localities of Italian Alps as well as between Tenerife and La Palma Islands of
the Canary archipelagos. The whole beam at the receiver was acquired and compared to models including the
local meteorological conditions.
Iqueye is a novel extremely high speed photon-counting photometer for the European Southern Observatory New
Technology Telescope in La Silla (Chile). Iqueye collects the light from the telescope through a few arcsec aperture, and
splits it along four independent channels, each feeding a single photon avalanche diode. The produced count pulses are
collected by a time-to-digital converter board and suitably time-tagged. Thanks to a rubidium oscillator and a GPS
receiver, an absolute rms timing accuracy better than 0.5 ns during one-hour observations can be achieved by postprocessing
the data. The system can sustain a count rate of up to 8 MHz uninterruptedly for an entire night of
observation.
After the first run in January 2009, some improvements have been evidenced and realized: a more practical mechanical
structure, a better optimization of the optical design, an additional filter wheel per each channel, a fifth photon counting
detector for monitoring the sky, a more interactive interface software. The updated Iqueye has been tested in December
2009, and the obtained results showed still better performance. As an example, the light curves of visible pulsars down to
the 25th visible magnitude have been obtained in a few hours of observation.
Iqueye is a single photon counting very high speed photometer built for the ESO 3.5m New Technology Telescope
(NTT) in La Silla (Chile) as prototype of a 'quantum' photometer for the 42m European Extremely Large Telescope (E-ELT).
The optics of Iqueye splits the telescope pupil into four portions, each feeding a Single Photon Avalanche Diode
(SPAD) operated in Geiger mode. The SPADs sensitive area has a diameter of 100 μm, with a quantum efficiency better
than 55% at 500 nm, and a dark count less than 50 Hz. The quenching circuit and temperature control are integrated in
each module. A time-to-digital converter (TDC) board, controlled by a rubidium oscillator plus a GPS receiver, time tags
the pulses from the 4 channels. The individual times are stored in a 2 TeraByte memory. Iqueye can run continuously for
hours, handling count rates up to 8 MHz, with a final absolute accuracy of each time tag better that 0.5 ns. A first very
successful run was performed in Jan 2009; both very faint and very bright stars were observed, demonstrating the high
photometric quality of the instrument. The first run allowed also to identify some opto-mechanical improvements, which
have been implemented for a second run performed in Dec 2009. The present paper will describe the first version, the
improvements implemented in the second one, and some of the obtained astronomical results.
Iqueye is a high speed astronomical photon counting device, tested at the ESO 3.5 m New Technology Telescope in La
Silla (Chile). The optics splits the telescope pupil into four portions each feeding a Single Photon Avalanche Diode. A
time-to-digital converter board time tags the pulses from the 4 channels, and the times sent to a storage device. The
instrument is capable of running continuously up to a rate of 8 MHz, with an absolute rms accuracy better that 0.5 ns.
The time is obtained by means of a rubidium clock referenced to UTC through the GPS signal. The paper describes the
analysis performed on data taken on bright stars in order to perform 'quantum-like' measurements in the photon stream,
namely the calculation of the second-order correlation functions g(2)(x,0) and g(2)(0,t). To this end, an ad hoc software
correlator has been developed. Taking advantage of the pupil-splitting concept, the calculation of g(2)(x,0) has been made
between the sub-apertures of the telescope, as a first step to verify the zero-baseline correlation coefficient in an
Hanbury-Brown Twiss intensity interferometer [1]. Our experiment demonstrates the value of an Iqueye-like instrument
applied to larger telescopes, like the four 8 m VLTs or the two 10m Keck telescopes, and even more the sub-pupils of the
future 42 m E-ELT for a novel exploitation of the photon stream from celestial objects.
Almost all astronomical instruments detect and analyze the first order spatial and/or temporal coherence properties
of the photon stream coming from celestial sources. Additional information might be hidden in the second
and higher order coherence terms, as shown long ago by Hanbury-Brown and Twiss with the Narrabri Intensity
Interferometer. The future Extremely Large Telescopes and in particular the 42 m telescope of the European
Southern Observatory (ESO) could provide the high photon flux needed to extract this additional information.
To put these expectations (which we had already developed at the conceptual level in the QuantEYE study for the
100 m OverWhelmingly Large Telescope to experimental test in the real astronomical environment, we realized
a small prototype (Aqueye) for the Asiago 182 cm telescope. This instrument is the fastest photon counting
photometer ever built. It has 4 parallel channels operating simultaneously, feeding 4 Single Photon-Avalanche
Diodes (SPADs), with the ability to push the time tagging capabilities below the nano-second region for hours
of 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, named
Iqueye, has been built for the 3.5 m New Technology Telescope (NTT) of ESO. Iqueye follows the same optical
solution of dividing the telescope pupil in 4 sub-pupils, imaged on new generation SPADs having useful diameters
of 100 micrometers, time jitter less than 50 picoseconds and dark-count noise less than 50 counts/second. The
spectral efficiency of the system peaks in the visible region of the spectrum. Iqueye operated very successfully at
the NTT in January 2009. The present paper describes the main features of the two photometers and present
some of the astronomical results already obtained.
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