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by Italo Foppiani

Università di Bologna - Dipartimento di Astronomia I.Foppiani, G.Cosentino, B.Marano. .

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by Italo Foppiani

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

  2. 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. Imaging area Amplifying register Output Serial register Low Light Level CCD (L3CCD or LLLCCD) 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. Financial contribution… (so far) • ~ 70+60 KEuro Universià di Bologna • ~ 30 KEuro OAB (laboratory instruments) 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. If needed performances are achieved in the lab, then… Photon counting CCDs as wavefront sensors for LBT A.O. systems

  6. 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 0.14 arcsec @ 850nm) Guide star WDS J02186+4017 mv:8 11” mv:7.2 WDS J8267+2432 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

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