Abstract
Ultra-short extreme ultraviolet pulses from the free-electron laser FLASH are characterized using terahertz-field driven streaking. Measurements at different ultra-short extreme ultraviolet wavelengths and pulse durations as well as numerical simulations were performed to explore the application range and accuracy of the method. For the simulation of streaking, a standard classical approach is used which is compared to quantum mechanical theory, based on strong field approximation. Various factors limiting the temporal resolution of the presented terahertz streaking setup are investigated and discussed. Special attention is paid to the cases of very short (∼10 fs) and long (up to ∼350 fs) pulses.
Highlights
Most Free-electron lasers (FELs) in the XUV and x-ray range operate in the self-amplified spontaneous emission (SASE) regime relying on stochastic processes, resulting in pulses varying on a shotto-shot basis [7, 8]
It has been shown that these measurements can provide photon pulse durations with very high temporal resolution, currently cannot be scaled to the burst mode structure of free-electron laser in Hamburg (FLASH). (3) A similar approach using an optical replica of the electron bunch modulation (‘optical afterburner’) [13] is potentially able to deliver single-shot pulse duration information but has so far not been demonstrated experimentally
The FEL was operated in single bunch mode at 10 Hz, with electron bunch charges altered from 0.08 nC up to 0.44 nC, leading to different XUV pulse durations from ∼10 fs to ∼350 fs (FWHM) as well as to XUV pulse energies ranging between only a few μJ at 7 nm to >100 μJ per pulse at 20 nm
Summary
Free-electron lasers (FELs) working in the extreme ultraviolet (XUV) and x-ray region deliver unrivalled intense pulses. THz streaking [14,15,16,17,18,19] on the other hand can overcome these limits and has the potential to deliver single-shot pulse duration information basically wavelength independent and over a large dynamic range (in pulse duration and FEL energy). It can be operated with repetition rates up to several hundred kHz (potentially even MHz).
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