FOS Instrument Science Report #127

"The FOS Scattered Light Model Software"
by Michael R. Rosa

Abstract excerpted from the report:

The FOS is a single pass spectrometer with blazed, ruled gratings.
Both the blue and the red side dectectors cover wide spectral ranges.
Therefore the FOS is subject to "scattered" light which has its origins
primarily in diffraction patterns of the gratings and the entrance 
apertures, as well as the micro roughness of gratings due to their
ruled surfaces.  These limitations are brought about by physical principles.
Additional scattering due to contamination of optical surfaces or un-
baffeled stray light might be present, although the analysis of
laboratory and of in-flight data of the FOS shows that the actual instrument
is very close to the performance anticipated from ideal optical surfaces.
Therefore, the contamination of observations by scattered light can be
predicted with reasonable accuracy.

The program BSPEC is an attempt to model the dispersion and diffraction
of light in the FOS with an accuracy sufficient for the estimation of
scattered light contaimination in standard FOS data.  It is a simplified,
and therefore much faster, version of the program MSPEC which is a one to
one software model of all relevant optical effects.