Contamination

[AlasaMorph]

Posted to CCD-world:
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Hi Chris and Outworlders!
    We had somewhat of the same problem with WYFFOS. The RGO's embedded CCD 
spectrograph. A similar halation would occur some hours after pumping and 
coooling. This camera utilised a Tek 1k CCD, with a field-flattener mounted 
directly in-front of the CCD. It was (fortunately) the f-f which got the 
mysterious deposit. 
    After several goes at attempting to find out what it was, we took a sample 
to be analysed at the Univ of Loughboro on their Mass spectrometer. It turned 
to be what we had suspected - vacuum grease. Unfortunately to that date on our 
single chip cameras we had used a tiny amount on the back on the chip to act as 
a thermal bond to the cold block. It looked as if - in WYFFOS, this was 
evaporating and finding its way on to the coolish surface of the f-f. I 
reemoved ALL the grease and we got the internals of WYFFOS thorougly clean and 
went for an indium and mica spacer sandwich on the back of the CCD (we had to 
use mica as the Tek substrate is connected to the package). We didnt have any 
more problem after this. I also replaced one of the single chip camera heads 
when it came back to RGO (for another reason). There was never any complaint or 
problem with these heads during their lifetime (we had 5/6 at one stage).

    Could this be the source of the problem. Even if its NOT vacuum grease - I 
went through our whole system looking for this sort of contaminant, including 
nearly, some WD40 (a lubricant) which I caught one of our electronics guys 
using to ease the maganin wire into the PTFE sleaving. I got him to redo the 
whole thing before it went any where near the camera!!!

    It was a long-winded, tedious process doing all this, but we won in the 
end!!

Good luck

Paddy
-- 
...Surfing in CyberSpace on the Wings of a Storm...     |
Email : apo at tightfit.demon.co.uk
Web   : www.tightfit.demon.co.uk/Images.html

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