Speaker
Description
We demonstrate sub-femtosecond hard X-ray free-electron laser (XFEL) pulse generation at SACLA, achieved through a robust and flexible scheme for additional electron bunch compression. The method leverages a reverse-energy chirp, driven by wakefields within the accelerating structures and longitudinal space charge effects. By employing a tunable R56 optics in a two Double Bend Achromat (DBA) dogleg, we further compress electron bunches just before the undulators. A key advantage is the ability to adjust the longitudinal pulse duration while keeping the downstream beam orbit and transverse envelope stationary, ensuring that lasing conditions remain optimized throughout the tuning process. This allows for a rapid and reproducible transition between standard SASE and sub-femtosecond operation modes without the need for extensive beam tuning. Experimental characterization using a single-shot spectrometer and ASE-based diagnostics confirms that this additional compression successfully produces pulse durations below 1 fs (FWHM) with pulse energies up to 60 uJ. This scheme provides a practical and scalable approach for attosecond-regime XFEL science, applicable to various facilities.
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