Two-color is an emerging mode of operation in x-ray Free Electron Laser (FEL) having the potential to expand the pump and probe experiments toward fs temporal resolution and to site-selective spectroscopy. A novel and quick to setup method for two-color x-ray generation is presented here. The approach is experimentally demonstrated at the hard x-ray branch of SwissFEL (Aramis) using a laser emittance spoiler(LES). A short laser pulse is overlapped at the peak of the primary photocathode laser causing a local increase of the electron bunch emittance. In this configuration, the x-ray FEL emission occurs only for the two unspoiled parts of the bunch. Due to the fact that the electron bunch acquires an energy chirp along the acceleration, the spoiled beam produces two x-ray pulses of individual duration of few tens of fs having 1% photon energy separation and a time delay controllable up to 100 fs. Different from other techniques, the present method relies on the standard FEL configuration and it does not require a dedicated accelerator and undulator setting. With the LES, we achieved high efficiency, high energy and spectral stability paired to an independent control of the duration and of the relative intensity of the two colors. The LES enables shot-to-shot switching between one and two-color FEL and further, it is compatible with high repetition-rate FELs, as it is not associated to electron beam losses such as in other two-color methods.
Radiofrequency (RF) transverse deflection structures (TDSs) are fundamental time-resolved diagnostics in x-ray free-electron lasers. Two x-band TDSs with variable polarization of the deflecting force were recently installed after the undulators of Athos, the soft x-ray beamline of SwissFEL. This contribution summarizes the experience gained over the last few months during the commissioning of the RF system and the measurements made during operations, focusing on the setup of the entire complex RF system, the calibration and the time-resolved measurement that, combined with an energy spectrometer, provides longitudinal phase-space measurements of extreme importance for the commissioning of the complex FEL schemes implemented in the Athos beamline.
Temporal diagnostics are essential to characterize and optimize the performance of free-electron lasers (FELs). We propose and demonstrate a new method to measure the temporal profile of electron and photon beams in FEL facilities. The approach utilizes the transverse wakefields generated by the electrons traveling through a corrugated structure installed after an undulator section of an FEL. Compared to the more standard radio-frequency deflector approach, the method is more cost-effective, less sensitive to arrival time jitter, but reconstruction of the beam profiles becomes more complicated. We present numerical and experimental results that demonstrate the feasibility of the method. The experiments were carried out at SwissFEL, the x-ray FEL facility at the Paul Scherrer Institute in Switzerland.
We present a new and simple method to generate two-color free-electron laser (FEL) pulses. In our scheme an electron bunch is quadratically tilted in the transverse direction and exhibits an energy chirp. The head and tail of the bunch are aligned to the undulator beamline and will lase, while the middle part of the bunch undergoes orbit oscillations and thus is unable to amplify the FEL radiation. Since the beam is energy chirped, the central wavelengths of the SASE amplification at the two aligned parts of the bunch are different. The beam tilt is introduced by a variation of sextupole strength in a bunch compressor section. We present simulation results of this new method for the hard X-ray FEL beamline Aramis at SwissFEL. This includes the general performance and tunability of the scheme, the requirements on the energy chirp and tilt generation, and adverse effects associated with the beam tilt.
Conference Committee Involvement (2)
X-Ray Free-Electron Lasers: Advances in Source Development and Instrumentation VI
27 April 2023 | Prague, Czech Republic
X-Ray Free-Electron Lasers: Advances in Source Development and Instrumentation
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