Normalized single-shot X-ray absorption spectroscopy at a free-electron laser.

Günter Brenner,Piter S Miedema,Christian David,Martin Beye,Siarhei Dziarzhytski,Benedikt Rösner

doi:10.1364/ol.44.002157

Abstract

A setup for dispersive X-ray absorption spectroscopy (XAS), employing a new reference scheme, has been implemented and tested at the soft X-ray free-electron laser (FEL) FLASH in Hamburg. A transmission grating was used to split the FEL beam into two copies (signal and reference). The spectral content of both beams was simultaneously measured for intensity normalization within the FEL bandwidth on a shot-to-shot basis. Excellent correlation between the two beams was demonstrated within a few percent for single bunch operation at 143 eV photon energy. Applying the normalization scheme, an absorption spectrum of a Gd2O3thin film sample was recorded around the Gd N4,5-edge photon energy of 143 eV, showing excellent agreement with a reference spectrum measured at a synchrotron. This scheme opens the door for time-resolved single-shot XAS with femtosecond time resolution at FELs.

Highlights

X-ray absorption spectroscopy (XAS) is one of the most frequently applied spectroscopic X-ray techniques due to its experimental simplicity and large information content for a variety of fields composing material science, biology, and chemistry [1,2,3]
In this Letter, we report on the implementation of a dispersive XAS method at the PG2 monochromator beamline [17] at FLASH, making use of an advanced reference scheme for normalization
Similar to the approach realized at SACLA [18] and LCLS [19] it employs a diffractive transmission grating (TG) with low line density, where the positive and negative first diffraction orders are used to provide two identical copies of the pulse for single-shot intensity normalization for each spectral sample

Summary

Provided under the terms of the OSA Open Access Publishing Agreement

X-ray absorption spectroscopy (XAS) is one of the most frequently applied spectroscopic X-ray techniques due to its experimental simplicity and large information content for a variety of fields composing material science, biology, and chemistry [1,2,3]. FELs provide femtosecond X-ray pulses at an unprecedented photon flux [9,10,11] ideal to study such ultrafast processes, the application of time-resolved XAS at free-electron lasers (FELs) with femtosecond time resolution is extremely challenging [12]. For time-resolved experiments, both extreme ultraviolet beams can be transmitted through the sample, while only the interaction point with one of the beams is overlapped with the optical femtosecond pump-probe laser of FLASH [20]. This allows for a proper normalization of pump-laser induced changes of the absorption.

Diffraction orders

Findings

Relative Transmission Error