Pulse energy measurement at the SXR instrument

Abstract

A gas monitor detector was implemented and characterized at the Soft X-ray Research (SXR) instrument to measure the average, absolute and pulseresolved photon flux of the LCLS beam in the energy range between 280 and 2000 eV. The detector is placed after the monochromator and addresses the need to provide reliable absolute pulse energy as well as pulse-resolved measurements for the various experiments at this instrument. This detector provides a reliable non-invasive measurement for determining flux levels on the samples in the downstream experimental chamber and for optimizing signal levels of secondary detectors and for the essential need of data normalization. The design, integration into the instrument and operation are described, and examples of its performance are given.

X-ray absorption spectroscopy using a self-seeded soft X-ray free-electron laser

“…The front-end enclosure gas detectors (calibrated by the so-called electron loss scan method) are of different type than the so-called "Gas Monitor Detector" (GMD) in the SXR beam line. The GMD is absolutely calibrated, so the mJ pulse energy is measured (not calculated) after the monochromator but in front of the KB optics to less than approximately 10% [32,33]. 1.311 310 20 ± 5 80 ± 5 a The total intensity is determined by the signal measured in the gas detector before any optical elements of the SXR beamline.…”

“…Data collection of the partial fluorescence yield (PFY) measurements were performed at the SXR instrument at the LCLS [29][30][31][32][33]35] as described by Mitzner et al in [24]. A schematic drawing of the set up including the self-seeding scheme of the FEL is depicted in Fig.…”

“…Soft x-ray L-and K-edge XAS in the 250-1000 eV range typically require a spectral resolution corresponding to 0.05%, hence the beam has to be passed through a grating monochomator (~20% reflectivity) with a bandwidth-narrowing exit slit, although it has been shown that at ~100 eV experiments without an exit slit can be performed [28]. As a consequence of these and related losses in typical soft x-ray beamlines, the monochromatic peak flux on the sample at the soft x-ray endstation (SXR) of LCLS is reduced to a few percent of the original peak flux depending on the selected resolving power [29][30][31][32][33]. This reduced monochromatic photon flux is a limitation in particular for L-edge absorption spectroscopy of 3d transition metal atoms for dilute samples such as metalloenzymes (~mM) and for more complex techniques that require a particularly high average flux such as inelastic x-ray scattering (RIXS) measurements that hold great potential for quantitative electronic structure analyses [4].…”

Зарядовое распределение ионов Kr, образуемых при рентгеновском облучении 1.3 keV

“…GMD доказали свою эффективность для измерения ин-тенсивности пучков в мягком рентгеновском диапазоне на FEL-установках FLASH (Hamburg) [3][4][5] и LCLS (Stanford) [6].…”

Non-invasive online wavelength measurements at FLASH2 and present benchmark

“…The gas monitor detector (GMD) (Richter et al, 2003;Tiedtke et al, 2008), for example, for measurements of the absolute pulse energy, is used at FLASH as well as LCLS, SwissFEL and European XFEL (Tiedtke et al, 2014;Moeller et al, 2015). In this context, the idea of using photoionization spectrometry of gas targets consequently came up as an alternative approach to online wavelength measurement (Wellhö fer et al, 2008).…”