Windows thickness

[Paul Jorden]

To Alain & colleagues:
> Am trying to figure out what thickness should a given CCD dewar
> window be. Does somebody know of a nice formula which would
> give a recommended thickness versus diameter.

I agree with the formulas given by Phillip MacQueen; I've used essentially the 
same ones.

> Otherwise, what are the experimental values of "working cameras"
> ( i.e. without pieces of glass of a once upon a time too thin
> camera window gone through the CCD ) for different diameters.
> The value I am interested in would be for a 15 micron 4K, i.e.
> 100 mm diameter.
>
We've used lots of 66mm diam windows, with 4mm thickness- safety factor ~6, with 
no problems. Spectrosil-B Fused Silica, polished. No extra radiation emmission 
either. More recently we've built our INTPF mosaic camera head. This has 135mm 
diam* 6.5mm thick similar window- safety factor ~ 4. We've pumped/ cooled it 
quite a few times with no problems.
Luppino (at IfA) used a 110mm window * 5mm- safety factor ~3. he told me he'd 
made 4 of them with no problems, but considered it a bit thin for comfort. In 
case you have'nt seen it his paper may be of interest to cryostat constructors:
[Luppino & Miller, 1992 PASP, 104, 215].

Best of luck, Paul
-------------------------------------------------------------------
E-mail:  prj at ast.cam.ac.uk         Machine: Kria.ast.cam.ac.uk
Royal Greenwich Observatory, Madingley Road, Cambridge, CB3 0EZ, UK.
Phone: +44 (0) 1223- 374000  \direct phone- 374811 \RGO Fax- 374700