1. Photon counting CCDs as wavefront sensors for LBT A.O. systems
Photon counting CCDs as wavefront sensors for LBT adaptive optics systems INAF - Osservatorio Astronomico di Bologna G.Bregoli, C.Ciattaglia, G.Innocenti. INAF - Osservatorio Astrofisico di Arcetri C.Baffa, V.Biliotti, E.Giani, S.Esposito, P.Salinari.
Università di Bologna - Dipartimento di Astronomia
I.Foppiani, G.Cosentino, B.Marano.
by Italo Foppiani
Photon counting CCDs as wavefront sensors for LBT A.O. systems

2. High sky coverage by means of natural guide stars
Why ?
sread= 1 (intensified CCD)
CCD readout noise in high speed applications is the limiting factor of sensitivity. Amplified CCDs allow same adaptive correction making use of a reference star fainter by about 1 magnitude with respect to conventional CCDs.
sread= 7 (conventional CCD)
High sky coverage by means of natural guide stars
(almost total except galactic poles ).
Lower need for laser guide stars systems
(expensive and technologically complex).
High flexibility in MCAO system
(both numerical and optical conjugation became possible).
Photon counting CCDs as wavefront sensors for LBT A.O. systems

3. Low Light Level CCD (L3CCD or LLLCCD)
Imaging area
Output
Amplifying register
Serial register
L3CCDs, made available by E2V (ex Marconi AT) since 2002, intensify the electron signal by means of an amplifying register driven by a high voltage phase (avalanche gain).
Goal:
Very low noise and high frame rate device based on L3CCD detector performances.
Main issues:
Development of a suitable controller (fast, accurate, with a very stable high voltage phase, etc.).
Characterisation of detector and control system in photon counting conditions.
Photon counting CCDs as wavefront sensors for LBT A.O. systems

4. Work in progress…. The optical bench Present state
Reading rate up to 8 Mpixels/second which means ~ 2 ms to read a 128x128 detector
Noise still too high because we are still optimising wiring and layout
The cryostat
Nitrogen cooling is needed in order to suppress dark current and its noise
The controller: FASTI-L3CCD
Designed in Arcetri from FASTI-NICS controller is now assembled and is being debugged in Bologna.
Photon counting CCDs as wavefront sensors for LBT A.O. systems

5. ~ 70+60 KEuro Universià di Bologna
Next steps
Next 1 – 2 months to develop and to test the electronic system
Characterisation of the amplifying process (weeks)
Complete characterisation of the sensor (months)
Planning and realizing the photon counting detector for LBT A.O. systems.
Financial contribution… (so far)
~ KEuro Universià di Bologna
~ 30 KEuro OAB (laboratory instruments)
If needed performances are achieved in the lab, then…
Photon counting CCDs as wavefront sensors for LBT A.O. systems

6. Photon counting CCDs as wavefront sensors for LBT A.O. systems
A side product…
We have assembled a speckle camera based on a commercial analog L3CCD camera and we have tested it at the Loiano telescope (1.5m diameter, Airy disk nm)
Guide star
WDS J
mv:8
11”
mv:7.2
WDS J
Simple shift and add of 2600 images, 20ms exposure each, in I band by using a guide star.
0.3”
~ 0.16”
mv= 8.5
Cross spectrum analysis of 800 images, 20ms exposure each, in I band (collaboration with G.Sedmak)
Photon counting CCDs as wavefront sensors for LBT A.O. systems