Measurement of the average local energy spread of electron beam via coherent harmonic generation

Zhang

et al. 2014

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Polarization switching of light sources is required over a wide spectral range to investigate the symmetry of matter. In this paper, we report the first experimental demonstration of the crossed-planar undulators technique at a seeded free-electron laser, which holds great promise for the full control and fast switching of the polarization of short-wavelength radiation. In the experiment, the polarization state of the coherent radiation at the second harmonic of the seed laser is switched successfully. The experimental results confirm the theory and pave the way for applying the crossed-planar undulators technique for seeded x-ray free-electron lasers.

mentioning

confidence: 99%

Polarization switching demonstration using crossed-planar undulators in a seeded free-electron laser

Zhang

et al. 2014

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“…Thus, CHG intensity is much higher than spontaneous emission even at the very beginning of the radiator. The intensity analysis of such coherent photon beam can be used to roughly estimate the temporal structure of the electron beam current and emittance [36], or precisely determine the averaged slice energy spread [37,38], while spatial profile studies, as we will show below, will allow one to optimize the electron beam trajectory, verify the undulator magnetic gap, and adjust the phase match between two undulator segments.…”

Section: Coherent Photon Beam Based Methodsmentioning

confidence: 99%

Coherent photon beam based diagnostics for a seeded extreme ultraviolet free-electron laser

Dai

et al. 2014

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Independently from conventional electron beam based procedures, the photon beam based diagnostic is an alternative way for electron trajectory alignment and commissioning of numerous undulator cells in high-gain short-wavelength free-electron lasers (FELs). In this paper, using the microbunched electron beam and the undulator fine-tuning technique, a novel method based on the spatial profile analysis of coherent harmonic radiation from individual or two consecutive undulator segments, the so-called coherent photon beam based diagnostic, is proposed for undulator alignment and commissioning in seeded FELs. The preliminary experimental results at the Shanghai deep ultraviolet FEL test facility are presented. It shows that the proposed method is effective and convenient in the electron beam trajectory control, the undulator magnetic gap verification, and the phase match between two undulator segments.

“…A large bunching factor at high harmonics relies on the formation of sharp density spikes, which requires large energy modulation amplitude. For an HGHG FEL, the energy modulation amplitude A should be n times larger than the initial energy spread to give a considerable value of bunching factor at nth harmonic [25,26]. However, as shown in Fig.…”

Section: Hghg and Eehg With Short Seed Pulsesmentioning

confidence: 99%

Slippage effect on energy modulation in seeded free-electron lasers with frequency chirped seed laser pulses

Wang

et al. 2013

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Free-electron lasers (FELs) seeded with external lasers hold great promise for generating high power radiation with nearly transform-limited bandwidth in the soft x-ray region. However, it has been pointed out that the initial seed laser phase error will be amplified by the frequency up-conversion process, which may degrade the quality of the output radiation produced by a harmonic generation scheme. In this paper, theoretical and simulation studies on frequency chirp amplification in seeded FEL schemes with slippage effect taken into account are presented. It is found that the seed laser imperfection experienced by the electron beam can be significantly smoothed by the slippage effect in the modulator when the slippage length is comparable to the seed laser pulse length. This smoothing effect allows one to preserve the excellent temporal coherence of seeded FELs in the presence of large frequency chirp in the seed laser. Our studies show that the tolerance on frequency chirp in the seed laser for generating nearly transformlimited soft x-ray pulses in seeded FELs is much looser than previously thought and fully coherent radiation at nanometer wavelength may be reached with current technologies.