An electron–ion coincidence spectrometer for commissioning of a synchrotron radiation beamline: Absolute photon intensity and content of higher harmonic radiation

Abstract

We describe the commissioning of a new electron–ion coincidence spectrometer used to diagnose the photon beam from a plane grating monochromator beamline at the ASTRID2 synchrotron radiation facility. The spectrometer allows determination of the absolute photon intensity by calibration to the photoabsorption cross sections of known gases, such as the rare gases Ar, Kr, and Xe presented here. The spectrometer operates at very low pressure (∼10−8–10−9 mbar) and—due to the coincidence electron–ion detection scheme—the detector efficiencies can be determined routinely; hence, the spectrometer can be recalibrated swiftly. By variation of a single potential of the spectrometer, the content of higher order radiation in the monochromatized synchrotron radiation can be analyzed. The layout and operation of the synchrotron radiation beamline at ASTRID2 and its additional photon diagnostic units are additionally described.

Secondary ionization of pyrimidine nucleobases and their microhydrated derivatives in helium nanodroplets

“…At the used experimental conditions (slit opening after the undulator and filters), a negligible contribution of higher-order radiation from the undulator is expected. 23 The relative photon flux is estimated from the yield of electron-H 2 O + coincidences detected from the background gas. 24 Electron spectra were inferred from the VMI by Abel inversion using the MEVELER reconstruction method.…”