Metachrome coating

[Tim Abbott]

Forwarded from Alistair Walker, CTIO:

> Subject: Metachrome coating
> 
> 
> 
> 
> At CTIO we have a Tektronix 2048 CCD which was made several
> years ago as part of the development for the HST STIS instrument.
> This CCD is front-illuminated with 21 micron pixels, and four
> years ago was coated with "metachrome" by Thomson, to give
> QE of 15-20% below 4700A.  We have been using this CCD at the
> Schmidt telescope for the past 12 months, where it gives over
> a one degree field.
> 
> A sudden occurence two weeks ago was the appearance of what
> looked like a long hair-like "crack" in the surface, this 
> meanders for many mm.  If the CCD is viewed with the naked eye
> the surface color of the coating is slightly different in the 
> regions near the defect.  When the latter is viewed in
> oblique illumination under a microscope, it is found to be 
> raised above the surroundings (ie is a hill) and there is no
> actual break in the coating.  
> 
> Our intrpretation is that the coating has partly de-laminated
> and the visible defect is the junction between the attached
> and the non-attached areas.  I would be interested in knowing
> whether anyone has had similar experience with these coatings
> becoming detached from large CCDs and, if it is necessary to
> remove the coating, what solvent works best.  We have been using
> Thomson 1024 CCDs with metachrome coatings for seven years with 
> no problems, but of course the Tek device is very much larger.
> 
> Alistair Walker
> 
>      
>    
> 


-- 
Timothy M. C. Abbott                http://www.cfht.hawaii.edu/~tmca/tmca.html