The results of these simulations show a strong interest in EMCCDs for AO wavefront sensors despite the fact they have lower red QE (because high resistivity silicon is yet untried) and an excess noise factor due to the electron multiplication process. In August 2004, a call for tenders was issued for the development and supply of 240^240 pixel, very low noise (1e- or less), fast readout (1.2 kframes/s) CCD detectors that meet the set requirements (see Table 1). This culminated in a contract between e2v and ESO in April 2005 to start a detector development. Full details of this detector development and trade-offs are presented in [2]. The technical challenges of the detector controller are detailed in [3]. This new detector will be used for the next generation of ESO instruments requiring AO systems, and among them the ESO VLT Planet Finder, a high contrast AO system dedicated to the research of extra-solar planets. Figure 3 illustrates a Peltier cooled package similar to the one that will be used for the CCD220.

To conclude, this study clearly shows that for an AO wavefront sensor, a low readout noise is more important than high red QE.

CCD1 ron=0 -OCC01 ron=0.5

CCD2 ran=2 CCD2 ron=3 CCD2 ron=5

GS magnitude

Figure 2. Strehl Ratio comparison of CDD1 (classical) and CCD2 (EMCCD) for a M5 type guide star (red guide star).

Table l. AO wavefront sensor detector main characteristics.




e2v technologies, UK

Name of the detector


Detector format

240x240 pixels, split frame transfer


EMCCD, excess noise factor 1.4

Number of outputs


Frame rate

25 Hz - 1.2 kHz

Read noise

< 1e- at 1.2 kHz frame rate

Figure 3. CCD65 Peltier cooling package. The AO CCD220 detector will use a similar Peltier package.

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook

Post a comment