Abstract
One of the most challenging tasks for extreme ultraviolet, soft and hard x-ray free-electron laser photon diagnostics is the precise determination of the photon pulse duration, which is typically in the sub 100 fs range. Nine different methods, able to determine such ultrashort photon pulse durations, were compared experimentally at FLASH, the self-amplified spontaneous emission free-electron laser at DESY in Hamburg, in order to identify advantages and disadvantages of different methods. Radiation pulses at a wavelength of 13.5 and 24.0 nm together with the corresponding electron bunch duration were measured by indirect methods like analyzing spectral correlations, statistical fluctuations, and energy modulations of the electron bunch and also by direct methods like autocorrelation techniques, terahertz streaking, or reflectivity changes of solid state samples. In this paper, we present a comprehensive overview of the various techniques and a comparison of the individual experimental results. The information gained is of utmost importance for the future development of reliable pulse duration monitors indispensable for successful experiments with ultrashort extreme ultraviolet pulses.9 MoreReceived 16 July 2014DOI:https://doi.org/10.1103/PhysRevSTAB.17.120702This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society
Highlights
One of the essential characteristics of the new generation of extreme ultraviolet (XUV) to x-ray free-electron lasers is their ultrashort pulse duration in the femtosecond range
One of the most challenging tasks for the free-electron laser (FEL) photon diagnostics is the precise determination of the FEL pulse duration
For the measurements that were performed at 13.5 nm, the FEL was tuned such that all pulses in the bunch train had roughly the same electron bunch and XUV pulse parameters
Summary
One of the essential characteristics of the new generation of extreme ultraviolet (XUV) to x-ray free-electron lasers is their ultrashort pulse duration in the femtosecond range. This opens up new opportunities for the detailed. From the experimental point of view, indirect methods are typically simpler to realize as compared to the direct approaches. There was one study comparing electron bunch duration measurements with the result of one indirect photon pulse duration determination technique [19]. Up to now there were no studies at FLASH or at any other XUV or x-ray FEL where many different methods were compared within one dedicated pulse duration measurement campaign (see Fig. 1). The aim of the campaign was to identify sensitive parameters of the electron bunch compression and to develop recipes for routine operation to reliably establish a specific user-requested XUV pulse duration at FLASH, especially for ultrashort pulses below 50 fs
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