STScI Logo

Hubble Space Telescope
GHRS Instrument Science Report 029

GHRS Instrument Science Report 029

GHRS Photocathode Granularity Calibration 03/90

Ronald L. Gilliland


The detector systems for the Goddard High Resolution Spectrograph on
HST are photon counting devices, as such they, in principle, should
support very high signal-to-noise observations. The limiting factor
for most GHRS observations in attaining high S/N will be the
characterization of the (2-dimensional) small-scale irregularity of the
photocathodes. In this technical note we discuss the physical problem
in need of calibration, usual assumptions concerning this calibration,
past and current plans, and make a recommendation for a favorable