Photometric calibration of the first three spectroscopic orders of an extreme-ultraviolet spectrometer by use of synchrotron radiation.

We report here a technique for determining the quantum throughput of a high-resolution, extreme-UV spectrometer by use of the National Institute of Standards and Technology's Synchroton Ultraviolet Radiation Facility at Gaithersburg, Md. (SURF-II). Observations were obtained at three different synchrotron operating energies with and without a magnesium fluoride filter and a tin-germanium filter. This calibration permits us to extract system efficiencies for three overlapping spectroscopic orders with uncertainties of 10-30%. The uncertainties quoted in this preliminary experiment were limited by the available time, and we propose that with minor refinements a significant improvement could be realized.