Calibrations of flat alkali acid phthalate crystals between 650 and 2400  eV using synchrotron radiation

We have developed a dual goniometer end-station using Stanford Synchrotron Radiation Lightsource, beamline 16-2, in the energy range of 650-2400 eV for crystal calibrations. Three alkali acid phthalate crystals [potassium acid phthalate (KAP), rubidium acid phthalate (RbAP), and cesium acid phthalate (CsAP)] with (001) Miller indices are used to demonstrate the capability of our current experimental setup. The beamline provides photon fluxes from about 10⁹ to 10¹¹photons/sec between 50 and 2400 eV, with an error less than 1% absolute energy, and energy resolution between 1250 and 1800 depending on the energy. Our crystal calibrations are limited to energies above 650 eV due to our selection of an Amptek 8 µm Be window fast SSD detector. Total reflectivity calibrations of the crystals can be performed by either angle or photon energy scans. Repeatability of rocking curve measurements is better than 2%. Calibration results show significant impacts of Rb L and Cs M absorption edges for reflectivity in this energy range. The results are compared with XOP calculations, a publicly available multi-lamellar (ML) model, with good agreement. This indicates that it is possible to predict performances of flat KAP and RbAP crystals in this energy range when using the ML model.