Re: ATM Advance in CCDs

[Kevin McCarthy <sigma@mediaone.net>]

Mel:
Ok, perhaps not quite on par, but still a sizable advance... I cited Kodak's
claim of 30% at 400 nm; this is lower than a thinned, back-illuminated SITe
512, which has a 63% QE at that wavelength.  On the other hand, it's an
order of magnitude greater than the KAF-0400's I've bought, which have a 400
nm QE of 3%!  An order of magnitude, especially if it's close to free,  is
hardly a subtle improvement.  At 600 nm, the new CCDs have a QE of 63%,
compared to the back illuminated SITe 512 at 84%, and a standard KAF chip at
34%. Integrated over the broad range of wavelengths, the ITO electrodes
essentially double the responsivity, which will be a welcome advance if
their claims of minimal cost impact bear out.  A few posts questioned the
dark current and/or performance at low light levels, alluding to previous
Kodak enhanced blue devices.   They did produce versions a year or two ago
which used the fluorescent-dye coating dodge to jack up the blue response.
I'm pretty sure that the problems refer to those devices, and that the ITO
electrodes in the newly announced CCDs should be "transparent" in this
regard.

Mel Bartels

> I'd hardly say that the 30% QE mentioned is 'performance on par' with
> back illuminated chips, since these chips are 65% to 85% depending on
> which part of the blue spectrum you are talking about...
>
> Using back illuminated chips makes the telescope into a different beast,
> and means that you can design telescopes for shorter exposures.
>
> --
> Clear skies, Mel Bartels
> http://www.efn.org/~mbartels