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Characterization of materials using an ultraviolet radiometric beamline at SURF III

The completion of the upgrade of the synchrotron facilities at the National Institute of Standards and Technology (NIST) has yielded a better characterized broadband source of ultraviolet (UV) radiation at the Synchrotron Ultraviolet Radiation Facility (SURF III). A cryogenic-radiometer-based facility that uses the monochromatized radiation from SURF III has been established on beamline 4 (BL-4) to characterize detectors and optical materials in the wavelength range 125 nm to 325 nm. This upgraded cryogenic radiometry facility will be used to measure the spectral responsivity of detectors in the UV with a relative standard uncertainty of less than 10−2. To demonstrate the capability of BL-4, we have performed a transmittance measurement of calcium fluoride (CaF2). Accurate transmittance measurements of optical materials in the UV are urgently needed to evaluate which materials are the best choices for use in making lenses for UV lithography. A study of CaF2 in spectral transmittance, surface scattering, and surface absorption is presented.