Streamlining Detector-based Radiometry at SURF III
NIST has maintained the Synchrotron Ultraviolet Radiation Facility (SURF) for nearly 6 decades as a light source for research and radiometry. Radiometric services included detector calibrations on various beamlines, lamp calibrations on beamline 3 and spectrometer calibrations on beamline 2.
The Ultraviolet Radiation Group is establishing a new beamline on SURF III that will consolidate all the detector calibrations and provide for expanded coverage from 3 nm to 400 nm on a single instrument. This capability will provide SI traceable calibrations with dramatically reduced the uncertainties through the implementation of cryogenic radiometry. The broad coverage from 3 nm to 400 nm comprises a unique capability that will now cover the extreme-ultraviolet, vacuum-ultraviolet, and ultraviolet spectral ranges. Previously, the calibrations in many segments of that range were not SI traceable and had large absolute uncertainties (e.g., the regions below 10 nm, between 92 nm to 116 nm, and many segments elsewhere).
Description of the new beamline
At the heart of the new beamline is a grating-crystal monochromator that covers a wide spectral range from the visible to the soft x-ray.
We provide a short technical description:
The synchrotron radiation is collimated by the first mirror and directed into the monochromator section. In the monochromator, a pair of optical elements –normal-incidence gratings, grazing incidence gratings, crystals, or mirrors (in any combination) – disperse the radiation. A second mirror focuses the radiation onto an exit slit. End-station instrumentation consists of a small reflectometer and a large instrument calibration chamber capable of testing optical components and assembled spacecraft instruments. Available measurements include reflectivity, transmission, and detector responsivity.
The two mirrors are off-axis paraboloids using 2° grazing angle (88° angle of incidence with respect to the mirror normal) and 10-m focal length.