NEXAFS at nitrogen K-edge and titanium L-edge using a laser-plasma soft x-ray source based on a double-stream gas puff target

Przemysław Wachulak,Andrzej Bartnik,Tomasz Fok,Łukasz Węgrzyński,Martin Duda,Henryk Fiedorowicz

doi:10.1063/1.5085810

Abstract

We present a possibility of reaching higher energy absorption edges of organic materials, beyond the carbon K-edge, in the near edge X-ray absorption fine structure (NEXAFS) spectroscopy technique using a compact laser-produced plasma soft X-ray (SXR) source based on a double-stream gas puff target. The source was optimized for emission in the SXR spectral range from 1.5 to 5 nm wavelength using the krypton/helium target. The emission spectrum of the source and the absorption spectrum of the investigated sample were measured simultaneously by means of a grazing incidence spectrometer, equipped with a single, large aperture diffractive element. Based on both spectra, the optical density was computed for the silicon nitride membranes in a transmission mode, to reveal the NEXAFS features near the nitrogen K-edge. Moreover, due to spectral narrowing of the SXR emission by the use of titanium filter, reaching the titanium L-edge was also possible. Multiple SXR pulse data were compared to single SXR pulse (single-shot) data as well as to the numerical simulations. In this paper, the detailed information about the source, spectroscopy system, and the results of NEXAFS measurements is presented and discussed.

Highlights

Near edge X-ray absorption fine structure (NEXAFS) spectroscopy refers to the fine modulation of the absorption coefficient near the absorption edge of the material, spanning approximately 30 eV above the absorption edge.1 It is a widely used tool for the observation of the physical properties and chemical environment of the measured sample as it probes unoccupied electronic states and holds element specific information.Typically, synchrotron radiation is used for NEXAFS2 and most of the large-scale facilities have at least one beamline dedicated to X-ray absorption fine structure spectroscopy
We demonstrate the possibility to perform NEXAFS measurements beyond the carbon K absorption edge using the laser-plasma soft X-ray (SXR) source based on a double stream gas puff target
The spectra on the left show the nitrogen K absorption edge, covering the photon energy range from 380 eV to 450 eV, obtained when the silicon nitride membrane was illuminated by the SXR light from the Kr plasma, which was spectrally narrowed by a Ti filter

Summary

Introduction

Synchrotron radiation is used for NEXAFS2 and most of the large-scale facilities have at least one beamline dedicated to X-ray absorption fine structure spectroscopy. In such beamlines, dedicated to NEXAFS, the sample is scanned in the energy domain by monochromatic radiation. Nitrogen, or oxygen, the use of laboratory-scale broadband soft X-ray (SXR) laser-produced plasma (LPP) sources is possible. Various NEXAFS systems based on LPP sources were already demonstrated, with solid or gas targets, including high order harmonic generation (HHG) sources reaching attosecond time scale in the keV energy range.. Sources based on a single gas jet allow for truly compact, desktop systems, but with low SXR production and resulting relatively long measuring times. HHG has strong and unquestionable advantage, on the other hand, of ultrashort pulses, which can be used for time-resolved studies on the fs/as scale, but only for repeatable processes, which behave in the same way for each HHG pulse, so one can accumulate a sufficient signal over many hundreds/thousands HHG EUV/SXR pulses.

Methods

Results

Conclusion