Abstract
Self-amplified spontaneous emission (SASE) pulses delivered by free electron lasers (FELs) are inherently fluctuating sources; each pulse varies in energy, duration, arrival time and spectral shape. Therefore, there is strong demand for a full characterization of the properties of SASE radiation, which will facilitate more precise interpretation of the experimental data taken at SASE FELs. In this paper, we present an investigation into the fluctuations of pulse duration, spectral distribution, arrival time and pulse energy of SASE XUV pulses at FLASH, both on a shot-to-shot basis and on average over many pulses. With the aid of simulations, we derived scaling laws for these parameters and disentangled the statistical SASE fluctuations from accelerator-based fluctuations and measurement uncertainties.
Highlights
Free-electron lasers (FELs) working in the extreme ultraviolet (XUV) and X-ray region deliver photon pulses with few-femtosecond duration and unrivalled intensity [1,2,3,4,5,6,7]
The majority of X-ray FELs operate in the self-amplified spontaneous emission (SASE) regime, meaning that each pulse is characterized by a unique combination of pulse energy, XUV spectrum, arrival time and pulse duration
This special mode enables the utilization of the zero order of the FEL photon beam for the pulse length diagnostic based on THz streaking [24], while the dispersed radiation is simultaneously used in the PG2 beamline to measure the FEL spectrum with high resolution [33]
Summary
Free-electron lasers (FELs) working in the extreme ultraviolet (XUV) and X-ray region deliver photon pulses with few-femtosecond (fs) duration and unrivalled intensity [1,2,3,4,5,6,7]. We present pulse-resolved measurements of the XUV pulse duration at the free-electron laser FLASH in Hamburg [1], achieved using THz streaking [22,23,24], in addition to measurements of the XUV spectrum and pulse energy of all individual pulses. The fluctuation of these parameters, as well as the correlations and dependencies between them are studied. The average and shot-to-shot fluctuations of the FEL photon pulse duration, energy, and arrival time are presented in Sec 4
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