Abstract
We demonstrate that the amplification of attosecond pulse in X-ray free electron laser (FEL) undulator can be tailored. The characteristic of the amplification of an isolated attosecond pulse in the FEL undulator is investigated. An isolated 180 attoseconds full width half maximum (FWHM) pulse at 1.25 nm with a spectral bandwidth of 1% is injected into an undulator. The simulation results show that for a direct seeding of 3MW, the seed is amplified to the peak power of 106 GW (40 μJ, an output pulse-width of 383 attoseconds) in the presence of a detuning at FEL resonance condition in 100-m long undulator. We note that the introduction of detuning leads to the better performance compared to the case without detuning: shorter by 15.5% in a pulse-width and higher by 76.6% in an output power. Tapering yields a higher power (116% increases in the output power compared to the case without detuning) but a longer pulse (15.4% longer in the pulse-width). It was observed that ± Δλ(r)/8 (Δλ(r)/λ(r) ~1%) is the maximum degree of detuning, beyond which the amplification becomes poor: lower in the output power and longer in the pulse duration. The minimum power for a seed pulse needs to be higher than 1 MW for the successful amplification of an attosecond pulse at 1.25 nm. Also, the electron beam energy-spread must be less than 0.1% for a suitable propagation of attosecond pulse along the FEL undulator under this study.
Highlights
Attosecond science has emerged as an important research area of ultrafast phenomena during the past decade [1] as it provides a direct access to capturing, measuring and controlling the electronic dynamics in atoms, molecules and condensed matters [2,3,4,5,6,7,8,9]
The amplification of a seeded attosecond pulse of a 180 attoseconds full width half maximum (FWHM), and 3 MW peak power with a spectral bandwidth of 1% is studied in an undulator which has a set of alternatively detuned undulator modules
Our study shows that a detuning in the resonance wavelength can tailor the attosecond pulse-width and can improve the output power
Summary
Attosecond science has emerged as an important research area of ultrafast phenomena during the past decade [1] as it provides a direct access to capturing, measuring and controlling the electronic dynamics in atoms, molecules and condensed matters [2,3,4,5,6,7,8,9]. The spectral properties obtained in a seeded FEL are strongly related to the spectral properties of the seed pulse, leading to the highly stable output spectra as demonstrated [22] All of these features are due to the efficient amplification because the seed power is in two orders of magnitude higher than the initial shot noise in an electron beam. This work mainly concentrates on the amplification characteristics of a seeded attosecond pulse with the variation of detuning in the FEL resonance wavelength. The minimum threshold to a seed power and the requirement of electron beam energy-spread are studied in view of radiation power and pulse-width.
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