Femtosecond x-ray free electron laser pulse duration measurement from spectral correlation function (original) (raw)
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Physical Review Letters, 2012
We determined the pulse duration of x-ray free electron laser light at 10 keV using highly resolved single-shot spectra, combined with an x-ray free electron laser simulation. Spectral profiles, which were measured with a spectrometer composed of an ultraprecisely figured elliptical mirror and an analyzer flat crystal of silicon (555), changed markedly when we varied the compression strength of the electron bunch. The analysis showed that the pulse durations were reduced from 31 to 4.5 fs for the strongest compression condition. The method, which is readily applicable to evaluate shorter pulse durations, provides a firm basis for the development of femtosecond to attosecond sciences in the x-ray region.
New Journal of Physics, 2011
Two-color, single-shot time-of-flight electron spectroscopy of atomic neon was employed at the Linac Coherent Light Source (LCLS) to measure laser-assisted Auger decay in the x-ray regime. This x-ray-optical cross-correlation technique provides a straightforward, non-invasive and online means of determining the duration of femtosecond (>40 fs) x-ray pulses. In combination with a theoretical model of the process based on the softphoton approximation, we were able to obtain the LCLS pulse duration and to extract a mean value of the temporal jitter between the optical pulses from a synchronized Ti-sapphire laser and x-ray pulses from the LCLS. We find that the experimentally determined values are systematically smaller than the length of the electron bunches. Nominal electron pulse durations of 175 and 75 fs, as provided by the LCLS control system, yield x-ray pulse shapes of 120 ± 20 fs full-width at half-maximum (FWHM) and an upper limit of 40 ± 20 fs FWHM, respectively. Simulations of the free-electron laser agree well with the experimental results.
Nature Photonics, 2014
Short-wavelength free-electron lasers (FELs) are now well established as essential and unrivalled sources of ultrabright coherent X-ray radiation. One of the key characteristics of these intense Xray pulses is their expected few-femtosecond duration. These properties pave the way for the highly anticipated investigations of a plethora of phenomena on the atomic scale in space and time, ranging from single-atom processes such as inner-shell multiple ionization all the way to biological systems, such as three-dimensional studies of viral genomes, diffraction tomography of whole cells and the dynamics of photosynthetic reactions. A prerequisite for any kind of timeresolved measurement is the precise characterization of the X-ray pulse duration. However, so far no measurement has succeeded in directly determining the temporal structure or even the duration of ultrashort FEL pulses in the few-femtosecond range. By deploying the so-called 'Streaking Spectroscopy' technique at the Linac Coherent Light Source free-electron laser we have been able to demonstrate a non-invasive scheme for temporal characterization of X-ray pulses with sub-femtosecond resolution. This method is independent of photon energy, decoupled from machine parameters and provides an upper bound on the X-ray pulse duration. Thus, we measured the duration of the shortest X-ray pulses available today to be on average not longer than 4.4 femtoseconds. In addition, an analysis of the pulse substructure indicates that the duration of a small percentage of the FEL pulses consisting of individual high-intensity spikes is of the order of only hundreds of attoseconds.
arXiv: Optics, 2018
In recent years X-ray Free Electron Lasers (XFELs) proved to be unmatched sources of ultrashort pulses of spatially coherent quasimonochromatic X-ray radiation. Diagnostics of XFEL emission properties, in particular pulse duration, spectrum and temporal profile is extremely important in order to analyze the experimental results. In this paper we propose a cost-effective method to examine these properties of Self-Amplified Spontaneous Emission (SASE) pulses. It only requires an ensemble of measured SASE spectra and provides the temporal autocorrelation of the ensemble-averaged Wigner distribution of SASE FEL pulses.
Few-femtosecond time-resolved measurements of X-ray free-electron lasers
Nature Communications, 2014
X-ray free-electron lasers, with pulse durations ranging from a few to several hundred femtoseconds, are uniquely suited for studying atomic, molecular, chemical and biological systems. Characterizing the temporal profiles of these femtosecond X-ray pulses that vary from shot to shot is not only challenging but also important for data interpretation. Here we report the time-resolved measurements of X-ray free-electron lasers by using an X-band radiofrequency transverse deflector at the Linac Coherent Light Source. We demonstrate this method to be a simple, non-invasive technique with a large dynamic range for single-shot electron and X-ray temporal characterization. A resolution of less than 1 fs root mean square has been achieved for soft X-ray pulses. The lasing evolution along the undulator has been studied with the electron trapping being observed as the X-ray peak power approaches 100 GW.
Ultrafast X-ray pulse characterization at free-electron lasers
Nature Photonics, 2012
The ability to fully characterize ultrashort, ultra-intense X-ray pulses at free-electron lasers (FELs) will be crucial in experiments ranging from single-molecule imaging to extreme-timescale X-ray science. This issue is especially important at current-generation FELs, which are primarily based on self-amplified spontaneous emission and radiate with parameters that fluctuate strongly from pulse to pulse. Using single-cycle terahertz pulses from an optical laser, we have extended the streaking techniques of attosecond metrology to measure the temporal profile of individual FEL pulses with 5 fs full-width at half-maximum accuracy, as well as their arrival on a time base synchronized to the external laser to within 6 fs r.m.s. Optical laser-driven terahertz streaking can be utilized at any X-ray photon energy and is non-invasive, allowing it to be incorporated into any pump-probe experiment, eventually characterizing pulses before and after interaction with most sample environments.
Single-shot spectro-temporal characterization of XUV pulses from a seeded free-electron laser
Nature Communications, 2015
Intense ultrashort X-ray pulses produced by modern free-electron lasers (FELs) allow one to probe biological systems, inorganic materials and molecular reaction dynamics with nanoscale spatial and femtoscale temporal resolution. These experiments require the knowledge, and possibly the control, of the spectro-temporal content of individual pulses. FELs relying on seeding have the potential to produce spatially and temporally fully coherent pulses. Here we propose and implement an interferometric method, which allows us to carry out the first complete single-shot spectro-temporal characterization of the pulses, generated by an FEL in the extreme ultraviolet spectral range. Moreover, we provide the first direct evidence of the temporal coherence of a seeded FEL working in the extreme ultraviolet spectral range and show the way to control the light generation process to produce Fourierlimited pulses. Experiments are carried out at the FERMI FEL in Trieste.