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Very fast photon counting photometers for astronomical applications
No full textThe topics treated in this thesis are the design, the integration and the use of the ultra-fast single photon photometer IQuEYE (Italian Quantum Eye). The implementation of this instrument represents an important step in a project, initiated in 2005, for the realization of a Quantum Photometer (QuantEYE) for the telescope EELT (European Extremely Large Telescope) of 42 meters in diameter, now under construction, which is scheduled for completion in 2018.
Such an instrument would represent a breakthrough in observational Astronomy and it would allow extending the knowledge gained from theoretical and experimental Quantum Optics to the Astrophysics. QuantEYE is designed to extract from the light collected the information enclosed in the statistical distribution of photons through spatial and temporal analysis of the correlation functions of order higher than first, beyond the capability of "classics" instrumentation.
The instrument described in this thesis, IQuEYE, is a prototype for NTT (ESO New Technology Telescope). It is essentially a fixed aperture photometer that collects light within a field of view of few arcseconds, dividing the telescope light beam into four equal parts, and focuses each sub-beam on an independent single photon-counting diode SPAD. The innovative photon time-tagging system is based on a rubidium atomic clock, corrected on long time scale the by means of a GPS signal. This system allows the identification of each photon with a relative precision better than 100ps and an absolute UTC precision of 500ps for an hour of observation. The instrument can identify in this way up to eight million photons per second, that means IQuEYE is able to sustain flows of photons up to a maximum rate of 8MHz. All arrival times, digitized at 25ps, are stored, in this way post-processing analysis and data reprocessing in time are allowed.
The first part of the thesis is devoted to the detailed description of the instrument, starting from design phase, with particular attention for opto-mecanics, to its integration.
IQuEYE is now fully operative and has already been used in three ob-servation campaigns at La Silla (Chile) during the months of January and December 2009 and July-August 2010. The thesis then collects the results of some observations performed and presents them in its second part, with the aim of demonstrating the potential of the instrument.
So a brief description of a first experiment for the feasibility of intensity interferometry is given. Moreover the observation of an exoplanetary transit which allows us to double the accuracy in determining the period of mid-transit, is described. Finally the results for the observation of rapidly varying objects (three optical pulsars) are exposed, together with some analysis tools developed specifically for our data. The acquired data have an excellent quality. Through their analysis the best determination of the Crab pulsar (PSR B0531 +21) period was achieved. Furthermore the optical light curves for PSR B0833-45 (weak pulsar in the Vela constellation, at the limits of visibility for NTT) and B0540-69.
In this way the validity of IQuEYE in HTRA High Time Resolution Astronomy has been demonstrated.Gli argomenti trattati in questa tesi sono la progettazione, l’integrazione e l’utilizzo del fotometro ultrarapido a conteggio di singolo fotone IQuEYE (Italian Quantum Eye). L’implementazione di questo strumento rappresenta un passo fondamentale in un progetto avviato nel 2005 che mira alla realizzazione di un fotometro quantistico, QuantEYE, per il telescopio EELT (European Extremely Large Telescope) di 42 metri di diametro, oggi in fase di costruzione, la cui ultimazione è prevista per il 2018.
Un tale strumento rappresenterebbe una svolta nell’astronomia osservativa, permettendo di estendere le conoscenze sviluppate nell’ambito dell’ottica quantistica teorica e sperimentale all’ambito astrofisico. QuantEYE è progettato per estrarre dalla luce raccolta le informazioni contenute nella statistica di distribuzione spaziale e temporale dei fotoni mediante l’analisi delle funzioni di correlazione di ordine superiore al primo, limite al quale si fermano gli strumenti astronomici “classici”.
Lo strumento descritto nella presente tesi, IQuEYE, è un prototipo destinato all’uso su NTT (ESO New Technology Telescope). Si tratta essenzialmente di un contatore di singoli fotoni progettato per raccogliere la luce suddividendo la pupilla del telescopio attraverso quattro canali indipendenti che utilizzano dei rivelatori di tipo SPAD. L’innovativo sistema di etichettatura temporale dei fotoni rilevati si basa su un orologio atomico al rubidio, per corregere la deriva del quale viene usato un segnale GPS interpolato su lunga scala temporale. Tale sistema permette di identificare ogni fotone con una precisione relativa migliore di 100ps ed una precisione assoluta riferita ad UTC di 500ps per un’ora di osservazione. Lo strumento è in grado identificare in questo modo fino ad otto milioni di fotoni al secondo, cioè di sostenere flussi di fotoni fino ad un limite massimo di 8MHz. Tutti i tempi di arrivo, digitalizzati a 25ps, vengono salvati e permettono l’analisi differita e la rielaborazione nel tempo.
La prima parte della tesi è dedicata alla descrizione dettagliata dello strumento, a partire dalla fase di progettazione, il disegno optomeccanico, fino alla sua integrazione.
IQuEYE è oggi perfettamente funzionante ed è stato già utilizzato in tre campagne osservative a La Silla (Cile) durante i mesi di gennaio e dicembre 2009 e luglio-agosto 2010. La tesi raccoglie quindi i risultati di alcune delle osservazioni effettuate e li presenta nella seconda parte, con l’intento di dimostrare le potenzialità dello strumento.
Vengono descritti sommariamente un primo esperimento di fattibilità per l’interferometria di intensità e l’osservazione di un transito esoplanetario che permette di raddoppiare la precisione nella determinazione del periodo di metà transito rispetto agli strumenti utilizzati da altri autori. Per finire sono esposti i risultati ottenuti nell’osservazione di oggetti rapidamente variabili, tre pulsar ottiche, e alcuni strumenti di analisi dati sviluppati specificatamente. I dati acquisiti hanno una qualità eccellente e hanno permesso di ottenere la miglior determinazione mai conseguita del periodo di pulsazione per PSR B0531+21 (la pulsar della nebulosa del Granchio). Sono inoltre state ricavate le prime curve di luce ottiche da decenni a questa parte per PSR B0833-45 (debole pulsar nella costellazione della Vela, ai limiti di visibilità per NTT) e per B0540-69. In questo modo la validità di IQuEYE nell’ambito dell’astronomia ad alta risoluzione temporale è stata ampiamente dimostrata
Aqueye Plus: a fast photometer with an optical vortex coronagraph
No full textEquipping a single-photon-counting multicolor photometer with an
optical vortex coronagraph and adaptive optics module constitutes a
two-path instrument for astronomical and industrial applications
Quantum Astronomy with Iqueye
No full textIqueye 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
Aqueye and Iqueye, Very-High-Time-Resolution Photon-Counting Photometers
No full textWe describe very high-time-resolution photometers capable of tagging the arrival time of each photon with a resolution and accuracy of few hundred picoseconds, for hours of continuous acquisition, and with a dynamic range of more than 6 orders of magnitude. The final goal is the conceptual definition of a ``quantum'' photometer for the E-ELT, capable of detecting and measuring second-order correlation effects in photon streams from celestial sources. Two prototype units have been built and operated, one for the Asiago 1.8-m telescope (AquEYE) and one for the 3.5-m NTT (IquEYE).Here we will present results obtained by IquEYE on the Crab Nebula pulsar in simultaneous radio observations with Jodrell Bank in December 2009
A First attempt to Intensity Interferometry with IQUEYE
Full text linkIntensity Interferometry is a technique for the calculation of stars angular diameters that could in
principle overcome some major disadvantages of traditional amplitude interferometry. This
technique was first applied in 1956 by Hanbury-Brown and Twiss (HBT) in Narrabri
(Australia), when they measured the diameter of several bright blue stars. Since then, the HBT
technique nearly disappeared from astrophysics. Nowadays theory and technology are mature
enough to guarantee a renewed exploitation of this effect in astronomy. Our group in Padua has
built Iqueye, a high speed astronomical photon counting device, first tested at the ESO 3.5m
New Technology Telescope (La Silla, Chile) in January 2009. With the collected data, a
posteriori we perform the calculation of g2(x,0) as a first step to verify the zero-baseline
correlation coefficient in a HBT intensity interferometer. In a similar way, g2(0,t) could be
calculated. To perform such calculations, a dedicated software correlator has been designed,
implemented and optimized and will be described in depth in the present paper. Although the
size of the NTT does not allow an acceptable signal to noise ratio for calculating second order
effects, our experiments demonstrate the value of an Iqueye-like instrument for HBT like
experiments. Hopefully an improved version of IQuEye applied to larger telescopes, like the
four 8m VLTs and even to the future 42m Extremely Large Telescope will be the perfect
instrument for a novel exploitation of the photon stream from celestial objects
METIS- ESA Solar Orbiter mission internal straylight analysis
No full textMETIS is the Multi Element Telescope for Imaging and Spectroscopy for the ESA Solar Orbiter. Its target is the
solar corona from a near-Sun orbit in two different spectral bands: the HI UV narrow band at 121.6 nm, and the
VL visible light band. METIS adopts a novel inverted externally occulted configuration, where the disk light is
shielded by an annular occulter, and an annular aspherical mirror M1 collects the signal coming from the
corona. After M1 the coronal light passes through an internal occulter and is then reflected by a second annular
mirror M2 toward a narrow filter for the 121.6 nm HI line selection. The visible light reflected by the filter is
used to feed a visible light (580 – 640 nm) polarimetric channel. The photospheric light passing through the
entrance aperture is back-rejected by a spherical rejection mirror.
Since the coronal light is enormously fainter than the photospheric one, a very tough suppression is needed for
the internal stray light, in particular the requirement for the stray light suppression is more stringent in the VL
than in the UV, because the emission of the corona with respect to the disk emission is different in the two
cases, and the requirements are a suppression of at least 10-9 times for the VL and a suppression of at least 10-7
times for the UV channel.
This paper presents the stray light analysis for this new coronographic configuration.
The complexity of the optomechanical design of METIS, combined with the faintness of the coronal light with
respect to the solar disk noise, make a standard ray tracing approach not feasible because it is not sufficient to
stop at the first generation of scattered rays in order to check the requirements. Also scattered rays down to the
fourth generation must be treated as sources of new scattering light, to analyze the required level of accuracy. If
used in a standard ray tracing scattering analysis, this approach is absolutely beyond the computational
capabilities today available; therefore we opted for a scattering ray generation with a Montecarlo method in
which after a father ray hits a surface, only one ray is generated, randomly selected according to the distribution
of the transmitted energy. These rays bring with them all the energy that is otherwise distributed between all the
rays of second generation, making the model more realistic and avoiding loss of energy due to the rays
sampling. The stray light has been studied in function of the mechanical roughness of the surfaces and the
obtained results indicate an instrument stray light blocking performance well within the requirements in both
channels
Results of Iqueye, a single photon counting very high speed photometer at the ESO 3.5m NTT in 2009
No full textIqueye 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. 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 over a
wide dynamic range. 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 both on optical pulsars and digital Hanbury
Brown – Twiss Intensity Interferometry
Preliminary internal straylight analysis of the METIS instrument for the Solar Orbiter ESA mission
No full textMETIS, the multi element telescope for imaging and spectroscopy, is a solar coronagraph foreseen for the Solar Orbiter
mission. METIS is conceived to observe the solar corona from a near-sun orbit in three different spectral bands: in the
HeII EUV narrow band at 30.4 nm, in the HI UV narrow band at 121.6 nm, and in the visible light band (500 – 650 nm).
The visible light from the corona is ten million times fainter than the light emitted by the solar disk, so a very stringent
light suppression design is needed for the visible channel. METIS adopts an “inverted occulted” configuration, where the
disk light is shielded by an annular shape occulter, after which an annular aspherical mirror M1 collects the signal
coming from the corona. The disk light heading through M1 is back-rejected by a suitable spherical mirror M0.
This paper presents the stray light analysis for this new-concept configuration, performed with a ray tracing simulation,
to insure the opto-mechanical design grants a stray light level below the limit of 10-9 times the coronal signal intensity. A
model of the optics and of the mechanical parts of the telescope has been realized with ASAP (Breault Research TM); by
means of a Montecarlo ray tracing, the effect of stray light on VIS and UV\EUV channels has been simulated
The optical pulsar B0540-69
No full textThe high speed photometer Iqueye has been used at the NTT in January and December 2009,
obtaining a series of data on the Crab, LMC and Vela pulsars. This paper describes in particular
the data obtained on PSR B0540-69 (the second brightest optical pulsar) and the derived light
curve. Conclusions are then drawn about the braking index and other characteristics
Optical phase coherent timing of the Crab nebula pulsar with Iqueye at the ESO New Technology Telescope
No full textThe Crab nebula pulsar was observed in 2009 January and December with a novel very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New Technology Telescope. Thanks to the exquisite quality of the Iqueye data, we computed accurate phase coherent timing solutions for the two observing runs and over the entire year 2009. Our statistical uncertainty on the determination of the phase of the main pulse and the rotational period of the pulsar for short (a few days) time intervals are ≈ 1 μs and ̃0.5 ps, respectively. Comparison with the Jodrell Bank radio ephemerides shows that the optical pulse leads the radio one by ̃ 240 μs in January and ̃ 160 μs in December, in agreement with a number of other measurements performed after 1996. A third-order polynomial fit adequately describes the spin-down for the 2009 January plus December optical observations. The phase noise is consistent with being Gaussian distributed with a dispersion σ of ≈ 15 μs in most observations, in agreement with theoretical expectations for photon noise-induced phase variability
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