MTF of UV flooded CCDs

[Peter Sinclaire]

Dear CCD fellows,

We are currently testing our first UV flooded CCD (a J. Geary's 2688x512
chip thinned by M. Lesser) which has an impressive RQE after UV flooding.
This CCD has been mounted on the CES (the ESO Coude Echelle Spectrograph)
and we are right now puzzled by a strange decrease in resolution after the
UV flooding. We got for exactly the same instrument setting a FWHM of 2.8
pixels before flooding and 3.3 after flooding. After thoroughly checking
the spectrograph parameters and alignment we could not yet find an
explanation for this phenomenum.

Has anybody measured the MTF at the blue end (300-400nm) of a UV flooded
CCD before and after the flooding? Were any differences found? Is it
possible that a similar effect like the known degradation of MTF on thick
devices at near IR wavelength could be happening here? (i.e. the
photoelectrons close to the surface which are pushed to the collecting
wells by the backside charging could be drifting to neighbour pixels?) 

Hope that somebody out there can give some hints a.s.a.p. as we have to
decide tomorrow what to do about this problem.

cheers,

Peter Sinclaire

============================== E.S.O. =================================
Peter Sinclaire                     e-mail: psinclai at eso.org (Internet)
Optical Detectors, TRS, La Silla            
European Southern Observatory       Tel:  +56 (2) 699-3425
P.O.Box 19001, Santiago 19, CHILE   Fax:  +56 (2) 695-4263
++++++++ Over 19 million pixels serving science every night! ++++++++++