Abstract
The THz-field-driven streak camera has proven to be a powerful diagnostic-technique that enables the shot-to-shot characterization of the duration and the arrival time jitter of free electron laser (FEL) pulses. Here we investigate the performance of three computational approaches capable to determine the duration of FEL pulses with complex temporal structures from single-shot measurements of up to three simultaneously recorded spectra. We use numerically simulated FEL pulses in order to validate the accuracy of the pulse length retrieval in average as well as in a single-shot mode. We discuss requirements for the THz field strength in order to achieve reliable results and compare our numerical study with the analysis of experimental data that were obtained at the FEL in Hamburg - FLASH.
Highlights
Short-wavelength pulses of ultra-short duration and high intensity as delivered by extreme ultraviolet (XUV) and X-ray free-electron lasers (FELs) have opened new frontiers in atomic and molecular physics, non-linear spectroscopy, solid density plasma physics, photochemistry, and structural biology [1,2,3,4,5]
The temporal phase of the XUV pulse is neglected by this approach and the temporal profile of the FEL pulse is retrieved by a direct projection of I(W, τ) onto the time axis [20,31,42]; (iii) Simplified chronocyclic tomography (CT) - this approach treats the streaking effect as a shear of the Wigner distribution on the time-axis [40,43,44] according to Eq (3)
We found no significant difference between the Gaussian approximation and the linear streaking approaches when applied at large streaking speeds
Summary
Short-wavelength pulses of ultra-short duration and high intensity as delivered by extreme ultraviolet (XUV) and (soft) X-ray free-electron lasers (FELs) have opened new frontiers in atomic and molecular physics, non-linear spectroscopy, solid density plasma physics, photochemistry, and structural biology [1,2,3,4,5]. To provide to a broad user community reliable information on the temporal structure of FEL pulses, a number of direct and indirect diagnostics techniques has been developed [18,19,20]. Indirect techniques enable a reliable prediction of the temporal characteristics of the FEL pulses Their verification and calibration requires photon pulse measurements in the time domain. We discuss the requirements for the THz field strength in order to achieve a reliable pulse length retrieval and use this knowledge to analyse streaking measurements performed at the FEL in Hamburg - FLASH. Our results help to optimize the THz based streak camera performance and contribute to the development of efficient data analysis routines in order to provide machine diagnostics and users of experimental end-stations with a fast and reliable feedback
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