Towards time resolved core level photoelectron spectroscopy with femtosecond x-ray free-electron lasers

A Pietzsch,C Gahl,E Suljoti,A Föhlisch,F Hennies,M Beye,A Melnikov,K Döbrich,M Deppe,W Wurth,M Nagasono

doi:10.1088/1367-2630/10/3/033004

Abstract

We have performed core level photoelectron spectroscopy on a W(110) single crystal with femtosecond XUV pulses from the free-electron laser at Hamburg (FLASH). We demonstrate experimentally and through theoretical modelling that for a suitable range of photon fluences per pulse, time-resolved photoemission experiments on solid surfaces are possible. Using FLASH pulses in combination with a synchronized optical laser, we have performed femtosecond time-resolved core-level photoelectron spectroscopy and observed sideband formation on the W 4f lines indicating a cross correlation between femtosecond optical and XUV pulses.

Highlights

Generation at optical lasers, even femtosecond dynamics have been investigated [35]
Our objective is to find suitable x-ray fluences per pulse for electron spectroscopy and derive a generally valid model based on the photon energy dependent photoionization crosssection and the target density
The statistics of the spectra vary due to the differences in the number of pulses accumulated with the respective number of photons per pulse, as displayed in the right-hand panel of figure 1, with the latter reflecting the probability distribution of pulse energies of free-electron laser at Hamburg (FLASH) resulting from the self amplified spontaneous emission (SASE) process

Summary

Introduction

Generation at optical lasers, even femtosecond dynamics have been investigated [35]. there we are restrained to some few wavelengths available from the high harmonics of the laser. If we want to use x-ray pulses for time resolved ESCA in a broad wavelength regime and up to high energies, we need to resort to free-electron lasers (FELs) capable of producing brilliant x-ray pulses up to kilo-electron-volt photon energies with less than 30 fs pulse duration. In this contribution, we establish the foundation for femtosecond time-resolved ESCA (fs-ESCA) on a solid surface using the free-electron laser at Hamburg (FLASH) [36] in combination with a synchronized optical laser. On the sample an optical excitation intensity of 4.62 × 1010 W cm−2 was reached

Objectives

Results

Conclusion