Gravitational and relativistic deflection of X-ray superradiance. Bertozzi, W. Nuclear resonance fluorescence excitations near 2 MeV in U and Pu C 78 Minitti, M. Nass K, et al. Protein structure determination by single-wavelength anomalous diffraction phasing of X-ray free-electron laser data. Warwick T, et al. Development of scanning X-ray microscopes for materials science spectromicroscopy at the Advanced Light Source. Synchrotron Radiat.
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Andriyash IA, et al. An ultracompact X-ray source based on a laser-plasma undulator. Pogorelsky, I. V et al. Sakai Y, et al. Observation of redshifting and harmonic radiation in inverse Compton scattering. Albert F, et al. Characterization and applications of a tunable, laser-based, MeV-class Compton-scattering gamma symbol-ray source. Duris, J. Inverse free electron laser accelerator for advanced light sources.
Beams 15 Sudar, N. Ovodenko A, et al. High duty cycle inverse Compton scattering X-ray source. Walker PA, et al. Manahan GG, et al. Single-stage plasma-based correlated energy spread compensation for ultrahigh 6D brightness electron beams. Advanced Accelerator Development Strategy Report.
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Ultrafast gating of a mid-infrared laser pulse by a sub-pC relativistic electron beam. Kimura, W. Detailed experimental results for laser acceleration staging. Beams 4 Hemsing E, et al. Highly coherent vacuum ultraviolet radiation at the 15th harmonic with echo-enabled harmonic generation technique. High efficiency energy extraction from a relativistic electron beam in a strongly tapered undulator Brown, W. Three-dimensional time and frequency-domain theory of femtosecond x-ray pulse generation through Thomson scattering. Beams 7 The physics of x-ray free-electron lasers.
Liu Y, et al. Experimental observation of femtosecond electron beam microbunching by inverse free-electron-laser acceleration. Oliva P, et al. Quantitative evaluation of single-shot inline phase contrast imaging using an inverse compton x-ray source. The attosecond nonlinear optics of bright coherent X-ray generation.
Weisshaupt, J. Ultrafast modulation of electronic structure by coherent phonon excitations. B 95 Jelinsky, S. Progress in soft X-ray and UV photocathodes. Spicer, W. Modern theory and applications of photocathodes. Tremsin, A. The quantum efficiency and stability of UV and soft x-ray photocathodes. In I, Tremaine, A. Fundamental and harmonic microbunching in a high-gain self-amplified spontaneous-emission free-electron laser. E 66 Andonian G, et al. Longitudinal profile diagnostic scheme with subfemtosecond resolution for high-brightness electron beams. Support Center Support Center. External link.
Undulator Radiation. Du kanske gillar. Spara som favorit. Skickas inom vardagar. The high scienti? In this book a particularly promising approach is described, the free-electron laser FEL , which is p- sued worldwide and holds the promise to deliver ultra-bright X-ray pulses of femtosecond duration. In the EUV region, it has been demonstrated that fully coherent pulses can be achieved by fine tuning the operation parameters of the seed laser and the dispersion section to compensate the combined effects from the beam energy curvature and the chirp developed during the FEL amplification 22 , For shorter wavelength, some novel schemes such as echo-enabled harmonic generation EEHG 24 , 25 and phase-merging enhanced harmonic generation PEHG 26 , 27 have been developed, and it has been demonstrated that the spectral bandwidth of EEHG is less sensitive to the nonlinear energy chirp of the electron 28 — These theoretical and experimental results pave the way for seeding a soft x-ray FEL directly from an ultraviolet laser.
But it is still a problem on how to mitigate the effect of the initial high order and random phase errors in the seed laser on the FEL output coherence. The longitudinal properties of the FEL pulse are largely determined by the distribution of the microbunching in the electron beam. It has been investigated that undulator sections resonant at sub-harmonics of the FEL wavelength can be used to enhance the FEL slippage, which provides an in situ method for communicating phase information over larger portions of the electron beam and improving the temporal coherence of a SASE FEL 31 , Similarly, we have proposed the idea of using a modulator resonant at sub-harmonics of the seed for slippage-boosting purpose in a seeded FEL However, for the proposed scheme with sub-harmonic modulation, the imperfection of the seed laser experienced by the electron beam can be significantly smoothed when the slippage length is comparable to the pulse length of the seed laser in the modulator.
This smoothing effect allows one to create a very uniform bunching distribution and preserve the excellent temporal coherence of seeded FELs in the presence of large phase distortions in the seed lasers.
Elettra Sincrotrone Trieste
In this paper, we report the first successful demonstration of using the slippage boosted spectral cleaning technique in a seeded FEL to generate fully coherent pulses from a seed laser with very large phase errors. The results suggest the possibility of generating fully coherent radiation pulse via harmonic up-conversion schemes with the assistance of the proposed technique.
The experiment setup is depicted in Fig. By tuning the magnet gap of the modulator, the undulator parameter K can be easily tuned from 0. The energy modulation is then converted into density modulation by the following magnetic chicane. After that, the electron beam is sent into the downstream variable gap radiator to generate coherent radiation at fundamental and harmonics of the seed.
The radiation properties can be detected with a charge-coupled device CCD and a spectrometer see Methods. Schematic layout of the experimental setup for testing the slippage boosted spectrum cleaning technique. A seed laser pulse with spectral phase errors a has been injected into the variable gap modulator to imprint an energy modulation on the electron beam. The energy modulation is converted into density modulation by the dispersion chicane.
The pre-bunched electron beam is sent into the variable gap radiator to generate coherent radiation at fundamental and harmonics of the seed which is detected by the downstream CCD and spectrometer.
The phase error can be eliminated b by using sub-harmonic modulation. To show the principle of the slippage boosted spectrum cleaning technique, three-dimensional simulations have been performed with the GENESIS numerical code 35 based on the parameters used in the experiment. To show the superior performance of the proposed technique, a seed laser pulse with second and third order spectral phase errors is utilized in the simulation.
The Wigner distribution function 36 , 37 was introduced to fully characterize the longitudinal properties of the laser pulse,. The Wigner distribution of the seed laser pulse together with the longitudinal profile and spectrum are illustrated in Fig. The seed laser interacts with a longitudinal uniform electron beam in the modulator. The spectral chirp only appears in the lateral parts of the radiation pulse, which has negligible effects on the spectral bandwidth.
This phenomenon has also been observed in other simulations in ref. In order to clearly show the spectral cleaning effect, high order dispersions have been induced by tuning the position and angle of the second grating in the compressor of the amplifier. Pulse characterization of the seed laser was performed with the second-harmonic generation frequency-resolved optical gating SHG FROG method The measurement results are summarized in Fig.
The third order dispersion causes an asymmetric delay of the pulse, resulting in parasite pulses in the temporal domain and sidebands in the spectral domain. With an ideal electron beam and suitable energy modulation amplitude, these large phase errors will be amplified by the harmonic up-conversion process and eventually destroy the longitudinal coherence at very high harmonics.
Longitudinal properties of the seed laser pulse measured with FROG. Experimental a and retrieved b FROG traces. Retrieved intensity and phase in the temporal c and spectral d domains. A CCD camera is utilized downstream of the radiator to detect the transverse spot and intensity of the harmonic radiation. The radiation properties in frequency domain can be investigated with a spectrometer see Methods.
Energy modulation was achieved when the electron beam and laser beam overlap spatially and temporally in the modulator see Methods. Various parameters such as the timing of the seed laser, the gaps of the undulators and the strength of the dispersion had been optimized to maximize the radiation power. Then the seed laser power has been optimized according to the spectrum of the radiation to avoid electron overbunching and radiation pulse splitting 22 , It is clearly shown that the spectra of CHG directly inherit the properties of the seed laser with similar bandwidth and apparent spectral sidebands.
Compared with the modulation at fundamental wavelength, the peak values of the output pulse energy are reduced by about 2—3 times for sub-harmonic modulations. The spectral sidebands are significantly reduced in Fig. These measurement results coincide with theoretical predictions and clearly show the spectral cleaning effect.
Spectrum cleaning of the fundamental radiation pulse with the slippage boosted effect in the modulator. One can find the similar cleaning effects that eliminated the sidebands in the spectra. The output bandwidth is reduced to about 1. For higher harmonic radiation, the output bandwidth of CHG will be broadened mainly due to two effects: the natural pulse shortening 16 , 21 , 39 , 40 and the phase error multiplication.
To make things clear, simulations were performed with experiment parameters but an ideal transform-limit Gaussian pulse as the seed laser. Excluding the pulse shortening effect, the bandwidth broadening for high harmonic radiation is mainly cause by phase error amplification.
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When the slippage length is shorter than the seed laser pulse length, i. The deviation between the experiment and simulation results becomes larger for higher harmonics due to the phase error multiplication. These results demonstrate the effectiveness of the slippage boosting effect for spectrum cleaning and generating nearly transform limited radiation pulses at high harmonics.
Comparison of output spectra at different harmonics of the seed. Comparison of output spectral bandwidths FWHM from experiment and simulations for different optimized conditions. Simulations are performed with an ideal Gaussian seed laser pulse red line. We have demonstrated the spectral cleaning method in a seeded FEL based on the slippage boosted effect in the modulator. It is found that, by adopting a sub-harmonic modulator to enhance the slippage length to a comparable level of the seed laser pulse length, the initial large phase errors can be significantly smoothed and the production of nearly transform-limited radiation pulses is possible.
The practicability of the proposed method depends on the application of it onto an x-ray FEL operated at very high harmonics with a seed laser with limited phase noises. The slippage boosted spectral cleaning method paves the way towards fully coherent x-ray generation with external seeded FEL schemes and provides a novel method for precisely controlling the temporal phase of ultra-short laser pulses. The linear accelerator LINAC consists of an S-band photo-injector, four S-band accelerating modules and a magnetic chicane as the bunch compressor.
The bunch compressor had been turned off during the experiment to minimize the possible effects from the nonlinear energy curvature on the final CHG spectrum. The undulator system consists of two stages of seeded FELs. The magnet gap of the radiator was tuned to The CCD camera and the spectrometer were placed close to an in-vacuum reflecting mirror downstream of the radiator.
- Slippage boosted spectral cleaning in a seeded free-electron laser.
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The intensity variation of the radiation pulse as a function of the modulator gap was measured by the CCD camera. By using Yttrium aluminum garnet screens before and after the modulator, the spatial overlap can be easily achieved by placing both the electron beam and laser beam on the same position.