Heydemann interpolation correction for energy linearization of soft X-ray monochromators.

Material science research in the soft-X ray regime at the Swiss Light Source accommodates five beamlines where the monochromators rely on in-vacuum angular encoders for positioning mirror and gratings. Despite the factory-calibration of the quadrature signals from these rotary encoders, the energy linearization for spectroscopic data requires accurate calibration of the encoder quadrature signals. We characterize the interpolation errors and describe the Heydemann correction algorithm for the quadrature signals for improving the energy linearization on a scale comparable with the incremental encoder interpolation interval. Experimental data are shown where such errors produce sizeable effects in soft-X ray spectroscopy and for which the correction algorithm efficiently improves the short-range non-linearity.