  The ultrathin X-ray entrance window for the spaceborne spectrometer SIXA was
characterised using synchrotron radiation. X-ray absorption fine structure near
the absorption edges of the constituting elements (aluminium, carbon, oxygen
and nitrogen) was measured. Large scale positional variations were also
studied. In addition, the opacity of the window was tested by observing the
effect of photocurrent in the detector generated by light leaked through the
window.
