Journal Club presentation Helena Pikhartova January 24, 2018
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Summary of article Using a radio-frequency in combination with a dipole spectrometer detector for: ✽ Single-shot extraction of a seeded FEL pulse profile ✽ Collection of information on the electron slice emittance and energy spread ”Diagnostic tools of this type are of utmost importance for future realization of compact electron guns, electron accelerators, and free-electron laser architectures.” 3/9
FEL introduction ✽ Invented in 1971 by John Madey ✽ FLASH (Free Electron Laser in Hamburg) - worlds first FEL designed and constructed for the extended ultraviolet and soft X-ray spectral range [1] Madey, J. M. J. Stimulated emission of bremsstrahlung in a periodic magnetic field. J. Appl. Phys. 42 (5), 19061913, doi:10.1063/1.1660466 (1971). 4/9
Experiment setup ✽ RF deflector installed at the exit of the radiator (f= 2 . 856GHz) shears the bunch vertically ✽ Energy spectrometer deflects the electrons horizontally ✽ Ce:YAG screen observes the distribution in the transverse planes 5/9
Results 1 Difference between unseeded and a seeded electron bunch. Concept of high-gain harmonic generation (HGHG) seeding: 6/9
Results 2 ✽ Reconstructed power profile from a typical seeded FEL ✽ Peak power P 0 = 429 MW ✽ Mean pulse length τ FEL = 78 . 0 ± 18 . 4 fs 7/9
✽ Varying relative timing between seed laser and electron bunch ✽ a-c longitudinal phase space distribution ✽ d-f power profile ✽ g peak power vs relative position of the seed laser ✽ h reconstructed emittance and measured energy spread 8/9
Related work Ultrafast X-ray pulse characterization at free-electron lasers ✽ http://rdcu.be/FnfP ✽ Temporal profile of individual FEL pulses with 5 fs full-width at half-maximum accuracy Measuring the temporal structure of few-femtosecond free-electron laser X-ray pulses directly in the time domain ✽ http://rdcu.be/Fnf9 ✽ Non-invasive scheme for temporal characterization of X-ray pulses with sub-femtosecond resolution 9/9
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