[vsnet-chat 2118] Re: Required CCD temperature stability

[aah@nofs.navy.mil]

Kato-san wrote:
>    My understanding was that the change in temperature causes the change
>in the length of the light path within CCD, thereby causing a different
>interference condition.  Am I right?  I've heard from our local observers
>that the fringe pattern of the old thinned TI chip was sensitive to
>the temperature variation.  If the temperature stability less than 0.5
>deg is practically adequate, considering both bias levels and fringes,
>we would be happy with our latest design of our new camera.
  Perhaps the old TI800x800 showed a variation with temperature, but I
haven't seen it on the SITe chip.  Of course, the problem here is that
we *do* temperature control to better than 0.5C, and therefore haven't
tried the experiment of changing temperature to check for any possible
variation.  I think 0.5C or better will be adequate.  The problem is
mainly that fringing exists, rather than subtle changes with small
temperature variations.  We find that the fringing is variable, depending
on the strength of the emission lines, and so some nights are fine while
others require offsetting the telescope between exposures to remove
the fringe effect.

>    We will be running a MPP mode.  I've heard the optimal temperature
>(-100 deg) from our local vendor.  Does your suggestion mean the optimal
>temperature would be higher for the MPP mode operation?
  I think you will find that MPP gets you small dark current at TEC temperatures
and saves much expense, since you don't have to use liquid nitrogen and its
associated storage costs.  What you lose is full well.  If you are cooling
to -100C anyway, then I would run non-MPP and get better full well/dynamic
range.  Also, non-MPP mode gives you some advantages, such as clocked
antiblooming and the ability to integrate under different gates to remove
some cosmetic defects.

Arne

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