THz streaking principle. Photoelectrons are emitted from free (noble gas) atoms ionized by short XUV pulses in the presence of a strong linearly polarized THz field, thus modifying the momentum component of the photoelectrons.
FLASH2 operates in the self-amplified spontaneous emission (SASE) regime and offers a large variety of sophisticated modes of operation, resulting in a unique combination of energy, spectrum, arrival time and pulse duration.
Thus, it is crucial to be able to precisely determine the pulse duration and arrival time of each pulse.
On the beamline FL28, which is currently being build up, a new few fs diagnostic setup based on angular streaking will be installed. The location of FL28 is chosen in a way, that an outcoupling mirror can reflect a part of the FEL beam to the pulse duration diagnostic, while the predominant part of the FEL beam propagates to the FLASH user end stations. This will allow the operation of an online pulse duration monitor with attosecond resolution, providing precise information on the SASE pulse durations used in the experiment.
In addition, a THz field-driven streaking setup has been installed (decommissioned 2024) at the FL21 beamline that was used to measure the single-shot pulse duration information. With this setup a large range of studies has been performed to e.g. determine the range of pulse durations that can be reliably be measured with such a setup.
In addition, correlations with other photon beam parameters (e.g. pulse energy, spectral distribution) have been investigated, as well as the evolution of the pulse duration of the fundamental and the third harmonic along the amplification process of the SASE radiation.
Using two opposing time-of-flight spectrometers in the THz streaking setup, a potential temporal wavelength chirp within the SASE pulse was quantified and compared to measurements of the electron longitudinal phase space.
References:
Angular streaking (first experiments at LCLS):
N Hartmann et al, Attosecond time–energy structure of X-ray free-electron laser pulses , Nature Photonics 12, 215 (2018) Article
Laser based THz streaking at FLASH:
I. Grguras, et al , Ultrafast X-ray pulse characterization at free-electron lasers,,
Nature Photonics 6, 852-857 (2012); Article
R.Ivanov, et al., Single-shot temporal characterization of XUV pulses with duration from ~10 fs to ~350 fs at FLASH , J. Phys. B.: At. Mol. Opt. Phys. 53, 184004 (2020); Article
I. Bermúdez et al., Study of temporal, spectral, arrival time and energy fluctuations of SASE FEL pulses, Optics Express 29, 10491-10508 (2021); Article
M. Bidhendi, et al FEL Pulse Duration Evolution along Undulators at FLASH,
Appl. Sci. 12, 7048 (2022); Article
R. Ivanov, et al. Free-electron laser temporal diagnostic beamline FL21 at FLASH,
Opt. Express 31, 19146-19158 (2023); Article
M. Bidhendi, et al. Determination of the XUV Frequency Chirp at the Free-Electron Laser FLASH via THz Streaking and Electron Beam Diagnostics,
Photonics 11,1153 (2024); Article
