Physics – Optics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003acs..rept....1w&link_type=abstract
ST-ECF Instrument Science Report ACS 2003-012, 23 pages
Physics
Optics
Hubble Space Telescope, Hst, Space Telescope Science Institute, Advanced Camera For Surveys, Acs
Scientific paper
The fringing of CCD detectors occurs because of interference between the incident light and the light internally reflected at the interfaces between the thin layers of the CCD chip. Knowing the construction of the CCD, namely the materials composing the layers, their refractive index variation with wavelength and their thicknesses, the resulting fringe amplitude can be calculated from geometrical optics. Malamuth et al. (2003) have applied this technique to the STIS CCD. The topmost layer, which is the detection layer and composed of Silicon, defines the most varying fringing with wavelength; the lower layers control the envelope of the fringing amplitude with wavelength. Modelling of the layer structure of the ACS HRC and WFC CCD's is described. The HRC (SITe) chip is a copy of the STIS one and so has a similar structure, but the WFC (also SITe) chip has proprietary construction. During the ACS ground testing at Ball Aerospace, a series of narrow band flat fields at wavelengths from 7000 to 10000A were observed to provide the primary data for the modelling. The modelling procedure is described. The observed fringe amplitude across the CCD is used to predict the spatial variation of the thickness of the top layer, whilst the thicknesses of the lower layers are kept fixed. By applying the model maps of the layer thicknesses to ground or in-orbits flats, the observed fringing in ACS can be reduced by a factor ~4 to the level of a few percent rms. Application of the fringe model to the correction of extracted spectra is outlined.
Freudling Wolfman
Pasquali Anna
Pirzkal Nor
Walsh Jonathan R.
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