new QE shuttering technique

[John Geary]

I have discovered a new way of "electronic shuttering" CCD response,
using the ION PUMP (of all things!).  Those of you with a perverse
point of view (most of you, I think) will find all sorts of new
uses for this valuable technique.

The trick is to take your Pt-flash-gated CCD from M. Lesser, put it
in a really clean dewar on a really clean vacuum pump, suck it
down, fill the dewar tank with LN2, and then turn the ion pump on
before anything gets very cold.  Everything looks great, including
the vacuum, until your go to take a flat or something.  Wow!  Here
are the results:

QE (400 nm) using the above:  1.5 %
QE (400 nm) after O2 soak:   97.7 %

(ML and I have discussed this a bit.  Maybe residual water vapor is
initially dissociated by the ion pump, allowing hydrogen poisoning
to develop??  Nothing bad happens if you wait for the dewar innards
to get very cold before lighting up the ion pump.)

So, what uses for the above 40 db attenuator can you think of?  How
about:
(1) Teaching tool for observers too young to remember photographic
plates.  (Hmmm. This probably includes many on this list !).
(2) Data throttle, for observers who were counting on bad weather
to get an urgent paper finished.
(3) April Fool joke for your favorite dickhead observer (you furnish
your own list).
Any more?
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John Geary
PADI DM-52283
geary at cfa.harvard.edu