Electron trajectory simulations of time-of-flight spectrometers for core level high-energy photoelectron spectroscopy at pulsed X-ray sources (original) (raw)
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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.
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.
Applications of laser streaking at X-ray free electron lasers
Bulletin of the American Physical Society, 2015
(XFEL) is revolutionizing the field of time resolved x-ray techniques. The availability of tunable pulses ranging from the soft to the hard x-ray region, and lasting only few tens of femtoseconds, or perhaps less, is enabling access to unprecedented temporal resolution. However, knowledge of the temporal properties of the x-ray pulses is poor, and synchronization to external sources introduces a timing jitter that dominates the fast dynamics and needs to be corrected for every shot. Using laser streaking techniques developed by the attosecond community, one can measure the pulse duration, and possibly improve the temporal resolution of pump probe experiments where electrons are collected to follow the processes by use of a self-referencing measurement. Illustration is presented following Auger decay in the time domain.
Femtosecond profiling of shaped x-ray pulses
New Journal of Physics, 2018
Arbitrary manipulation of the temporal and spectral properties of x-ray pulses at free-electron lasers would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the free-electron laser driving electron bunch can be tuned to emit a pair of x-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the x-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fully suppressed. Therefore, the ability to directly characterize the x-rays is essential to ensure precise and consistent control. In this work, we have generated x-ray pulse pairs via electron bunch shaping and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. This achievement completes an important step toward future x-ray pulse shaping techniques. Free-electron lasers (FELs) operating from the extreme ultraviolet to the hard x-ray spectral regime emit femtosecond pulses that are nearly ten orders of magnitude brighter than pulses generated by any other femtosecond x-ray source [1-4]. Such intense pulses have enabled new classes of experiments across a broad range of disciplines [5] in the natural sciences including structural biology [6-8], femtochemistry [9, 10], solidstate physics [11-13], and high energy density science [14, 15]. To rapidly build on proofof-principle experiments and initial demonstrations of new techniques, even greater control over the x-ray pulse properties is desirable. Manipulation of the driving electron beam presents a clear route to gain control over the FEL emission. For example, at x-ray FELs based on self-amplified-spontaneous-emission (SASE), the duration of the FEL pulse is
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.