Single shot spatial and temporal coherence properties of the SLAC Linac Coherent Light Source in the hard x-ray regime

We measured the transverse and longitudinal coherence properties of the Linac Coherent Light Source (LCLS) at SLAC in the hard x-ray regime at 9 keV photon energy on a single shot basis. Speckle patterns recorded in the forward direction from colloidal nanoparticles yielded the transverse coherence properties of the focused LCLS beam. Speckle patterns from a gold nanopowder recorded with atomic resolution allowed us to measure the shot-to-shot variations of the spectral properties of the x-ray beam. The focused beam is in the transverse direction fully coherent with a mode number close to 1. The average number of longitudinal modes behind the Si(111) monochromator is about 14.5 and the average coherence time τ(c)=(2.0±1.0) fc. The data suggest a mean x-ray pulse duration of (29±14) fs behind the monochromator for (100±14) fc electron pulses.     

Femtosecond and subfemtosecond x-ray pulses from a self-amplified spontaneous-emission-based free-electron laser

We propose a novel method to generate femtosecond and subfemtosecond photon pulses in a free-electron laser by selectively spoiling the transverse emittance of the electron beam. Its merits are simplicity and ease of implementation. When the system is applied to the Linac Coherent Light Source, it can provide x-ray pulses the order of 1 fs in duration containing about 10(10) transversely coherent photons.     

Explosions of xenon clusters in ultraintense femtosecond x-ray pulses from the LCLS free electron laser

Explosions of large Xe clusters ( ~ 11,000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 10(17) W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.     

Experimental verification of the chemical sensitivity of two-site double core-hole states formed by an x-ray free-electron laser

We have performed x-ray two-photon photoelectron spectroscopy using the Linac Coherent Light Source x-ray free-electron laser in order to study double core-hole (DCH) states of CO2, N2O, and N2. The experiment verifies the theory behind the chemical sensitivity of two-site DCH states by comparing a set of small molecules with respect to the energy shift of the two-site DCH state and by extracting the relevant parameters from this shift.     

Angle-resolved electron spectroscopy of laser-assisted Auger decay induced by a few-femtosecond x-ray pulse

Two-color (x-ray+infrared) electron spectroscopy is used for investigating laser-assisted KLL Auger decay following 1s photoionization of atomic Ne with few-femtosecond x-ray pulses from the Linac Coherent Light Source. In an angle-resolved experiment, the overall width of the laser-modified Auger-electron spectrum and its structure change significantly as a function of the emission angle. The spectra are characterized by a strong intensity variation of the sidebands revealing a gross structure. This variation is caused, as predicted by theory, by the interference of electrons emitted at different times within the duration of one optical cycle of the infrared dressing laser, which almost coincides with the lifetime of the Ne 1s vacancy.     

AMO instrumentation for the LCLS X-ray FEL

Instrumentation is being developed to conduct atomic, molecular and optical science experiments at the Linac Coherent Light Source x-ray free electron laser at the Stanford Linear Accelerator Center. This suite of instruments will be used to study the interaction of the very intense x-ray beam with the simplest forms of matter, namely atoms, molecules and clusters. The instrumentation will be ready for the start of operations of the facility in August 2009.     

Indo‐French meeting on indus‐2 and soleil

With the availability of the first generation of X-ray free electron lasers, pump-probe measurements with femtosecond resolution and high brilliance are now possible. For condensed matter systems, a wealth of modes in the mid-infrared (MIR) and terahertz (THz) regime determine the physics such that targeted excitation with ultrashort pulses at long wavelength becomes an important tool. We will briefly discuss the methodology of pump-probe experiments at the Linac Coherent Light Source (LCLS) and then review methods of generation of intense THz and MIR pulses. This is followed with recent examples from atomic and condensed matter physics at LCLS, and we conclude with an outlook of future developments in this field.     

Observation of shot noise suppression at optical wavelengths in a relativistic electron beam

Control of collective properties of relativistic particles is increasingly important in modern accelerators. In particular, shot noise affects accelerator performance by driving instabilities or by competing with coherent processes. We present experimental observations of shot noise suppression in a relativistic beam at the Linac Coherent Light Source. By adjusting the dispersive strength of a chicane, we observe a decrease in the optical transition radiation emitted from a downstream foil. We show agreement between the experimental results, theoretical models, and 3D particle simulations.     

Shearing interferometer for quantifying the coherence of hard x-ray beams

We report a quantitative measurement of the full transverse coherence function of the 14.4 keV x-ray radiation produced by an undulator at the Swiss Light Source. An x-ray grating interferometer consisting of a beam splitter phase grating and an analyzer amplitude grating has been used to measure the degree of coherence as a function of the beam separation out to 30 microm. Importantly, the technique provides a model-free and spatially resolved measurement of the complex coherence function and is not restricted to high resolution detectors and small fields of view. The spatial characterization of the wave front has important applications in discovering localized defects in beam line optics.     

Pair production from vacuum at the focus of an X-ray free electron laser

There are definite plans for the construction of X-ray free electron lasers (FEL), both at DESY, where the so-called XFEL is part of the design of the electron–positron linear collider TESLA, as well as at SLAC, where the so-called Linac Coherent Light Source (LCLS) has been proposed. Such an X-ray laser would allow for high-field science applications: one could make use of not only the high energy and transverse coherence of the X-ray beam, but also of the possibility of focusing it to a spot with a small radius, hopefully in the range of the laser wavelength. Along this route one obtains very large electric fields, much larger than those obtainable with any optical laser of the same power. In this Letter we discuss the possibility of obtaining an electric field so high that electron–positron pairs are spontaneously produced in vacuum (Schwinger pair production). We find that if X-ray optics can be improved to approach the diffraction limit of focusing, and if the power of the planned X-ray FELs can be increased to the terawatt region, then there is ample room for an investigation of the Schwinger pair production mechanism.     

Ultrafast x-ray diffraction using a streak-camera detector in averaging mode

We demonstrate an apparatus for measuring time-dependent x-ray diffraction. X-ray pulses from a synchrotron are diffracted by a pair of Si(111) crystals and detected with an x-ray streak camera that has single-shot resolution of better than 1 ps. The streak camera is driven by a photoconductive switch, which is triggered by 100-fs laser pulses at a repetition rate of 1 kHz. The laser and the streak camera are synchronized with the synchrotron pulses. In the averaging mode, trigger jitter results in 2-ps temporal resolution. We measured the duration of 5-keV pulses from the Advanced Light Source synchrotron to be 70ps.     

Coherent X-ray diffraction radiation produced by microbunched beams passing close to the edge of a slab

With use of formulas for single-particle X-ray transition and diffraction radiation (XTR and XDR), we obtain expressions for spectral-angular distributions and total numbers of emitted quanta in coherent X-ray transition radiation (CXTR2) and coherent X-ray diffraction radiation (CXDR) arising when a microbunched beam of electrons, respectively, intersects the interfaces of a slab or flies at small distance from the edge of the slab. Comparison of obtained results with those known for CXTR from a single interface is performed. It is shown on the basis of numerical calculations that experimental study of CXDR is at present possible on the Linac Coherent Light Source (LCLS, SLAC).     

Measurement of femtosecond atomic lifetimes using ion traps

Two types of experiment are described that both employ an electron beam ion trap for the production of highly charged ion species with the aim of then measuring atomic level lifetimes in the femtosecond range. In one experiment (done by Beiersdorfer et al. some time ago), the lifetime measurement depends on the associated line broadening. In a recent string of experiments at Linac Coherent Light Source Stanford, the HI-LIGHT collaboration employed pump-probe excitation using the FEL as a short-pulse X-ray laser.     

褶皱管束流能量稳定器(英文)

输出脉冲稳定性的需求对驱动自由电子激光产生的电子直线加速器装置束流稳定性提出了严格的要求,包括电子束平均能量、峰值流强、束团到达时间抖动和横向位置抖动等参数。基于正在建设的大连相干光源用户装置,探讨了最近提出的褶皱管用作能量稳定器的可行性。采用解析计算和数值模拟结合的方法,结合大连相干光源直线加速器的设计,在设计参数条件下能量稳定性至少提升10%。同时提供了褶皱管尾场设计的一般步骤。     

LCLS/SSRL Users' Meeting and Workshops Draw Hundreds to SLAC

Three hundred participants learned about the latest scientific capabilities at the Stanford Synchrotron Radiation Lightsource (SSRL) and Linac Coherent Light Source (LCLS) during the 2012 LCLS/SSRL Users' Meeting. The event included several workshops and sessions focused on specific science areas as well as talks about the latest scientific trends, challenges, and calls for more public outreach to spread the word about light source science.     

A novel method for resonant inelastic soft X‐ray scattering via photoelectron spectroscopy detection

A method for measuring resonant inelastic X‐ray scattering based on the conversion of X‐ray photons into photoelectrons is presented. The setup is compact, relies on commercially available detectors, and offers significant flexibility. This method is demonstrated at the Linac Coherent Light Source with ～0.5 eV resolution at the cobalt L₃‐edge, with signal rates comparable with traditional grating spectrometers.     

News & views: New Scientific Opportunities at the European Synchrotron Radiation Facility

Approximately 400 participants learned about the latest scientific capabilities at the Stanford Synchrotron Radiation Lightsource (SSRL) and Linac Coherent Light Source (LCLS) during the 2013 Users' Meeting at the SLAC National Accelerator Laboratory, October 1–4, 2013. The Users' Meeting included more than a dozen workshops as well as scientific awards, poster presentations, and talks on the latest scientific trends, challenges, and opportunities.     

PULSE Ultrafast X-ray Summer School

The Third Annual Ultrafast X-ray Summer School (UXSS 2009) was held from June 15–19, 2009, at the SLAC National Accelerator Laboratory (SLAC) and sponsored by the PULSE Institute for Ultrafast Energy Science. The summer school was a weeklong residential event that brought together about 100 students, post-doctoral researchers, and other young and established scientists from diverse backgrounds. Particular emphasis was given to new scientific opportunities enabled by the world's first hard X-ray free electron laser, the Linac Coherent Light Source (LCLS), which underwent a spectacular start-up only months before.     

Time-Resolved Crystallography at X-ray Free Electron Lasers and Synchrotron Light Sources

Serial femtosecond crystallography with biological macromolecules is a rapidly developing method tailored to the immense brilliance of the emerging free electron lasers for hard X-rays (X-ray FELs). Recently, the first successful time-resolved serial femtosecond crystallographic experiment at near atomic resolution was conducted at the Linac Coherent Light Source. The X-ray FEL-based experiments will trigger new developments not only at the X-ray FELs, but also at existing synchrotron light sources. This review will attempt to summarize some of the most important experiments to date and give a brief outlook on what to expect.     

User Workshop on High-Power Lasers at the Linac Coherent Light Source

A two-day international workshop on the physics and integration of high-power lasers with the Linac Coherent Light Source was held in Stanford, California, USA, on October 1–2, 2013. The workshop was co-organized by UC Berkeley, Lawrence Berkeley, Lawrence Livermore, and SLAC National Accelerator Laboratories. More than 150 scientists, including 30 students and postdocs who are working in high-intensity laser-matter interactions, fusion research, and dynamic high-pressure science, came together from North America, Europe, and Asia. The group discussed the most promising and important new physics experiments that will be enabled by the unique combination of high-power lasers and the world-class LCLS free-electron laser X-ray beam.