Free electron laser pulse characterization by THz streaking

The goal of this dissertation was to investigate a reliable single-shot pulse duration diagnostic tool for the pulse duration and wavelength range delivered at the Free Electron LAser of Hamburg (FLASH). At Self-Amplified-Spontaneous-Emission-based free-electron lasers (FELs), the radiation parameters - duration, arrival time, energy, spectrum, and spatial distribution - differ for each pulse. A dedicated single-shot diagnostic tool for each parameter is therefore essential in order to interpret the experimental data on a pulse-to-pulse basis.This work summarizes the effort to realize a temporal diagnostic tool using the streaking technique by building a terahertz (THz) "streak camera". The setup was prepared and calibrated, and various pulse duration measurements with different experimental settings were performed in order to explore and validate the application range of the streaking method. The aspects limiting the temporal resolution using the commissioned streaking setup were characterized experimentally. The pulse duration measurements were analyzed using classical and quantum mechanical streaking theory models.Furthermore, a deep statistical study on the SASE fluctuations was realized using single-shot measurements of various radiation parameters. Scaling laws were derived using theoretical simulations and the measured data. This analysis enabled the intrinsic statistical SASE fluctuations to be disentangled from accelerator-based fluctuations and measurement uncertainties

FEL pulse duration evolution along undulators at FLASH

Self-amplified spontaneous emission (SASE) free-electron lasers (FELs) deliver ultrashort pulses with femtosecond duration. Due to the fluctuating nature of the radiation properties of SASE FELs, characterizing the FEL pulses on a single shot basis is necessary. Therefore we use terahertz streaking to characterize the temporal properties of ultra-short extreme ultraviolet pulses from the free electron laser in Hamburg (FLASH). In this study, the pulse duration as well as the pulse energy are measured in a wavelength range from 8 to 34 nm as function of undulators contributing to the lasing process. The results are compared to one-dimensional and three-dimensional, time-dependent FEL simulations

Study of temporal, spectral, arrival time and energy fluctuations of SASE FEL pulsesb

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

Free-electron laser temporal diagnostic beamline FL21 at FLASH

A beamline for temporal diagnostics of extreme ultraviolet (XUV) femtosecond pulses at the free-electron laser in Hamburg (FLASH) at DESY was designed, built and put into operation. The intense ultra-short XUV pulses of FLASH fluctuate from pulse to pulse due to the underlying FEL operating principle and demand single-shot diagnostics. To cope with this, the new beamline is equipped with a terahertz field-driven streaking setup that enables the determination of single pulse duration and arrival time. The parameters of the beamline and the diagnostic setup as well as some first experimental results will be presented. In addition, concepts for parasitic operation are investigated