The Phase-Contrast Imaging Instrument at the Matter in Extreme Conditions Endstation at LCLS

We describe the Phase-Contrast Imaging instrument at the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Light Source. The instrument can image phenomena with a spatial resolution of a few hundreds of nanometers and at the same time reveal the atomic structure through X-ray diffraction, with a temporal resolution better than 100 femtosecond. It was specifically designed for studies relevant to High-Energy-Density Science and can monitor, e.g., shock fronts, phase transitions, or void collapses. This versatile instrument was commissioned last year and is now available to the MEC user community

Single-Shot Spectrometry for X-Ray Free-Electron Lasers

An experimental scheme to realize single-shot spectrometry for the diagnostics of x-ray free-electron lasers (XFELs) is presented. The combination of an ultraprecisely figured mirror and a perfect crystal form a simple, high-precision spectrometer that can cover an energy range from a few eV to a hundred eV with high resolution. The application of the spectrometer to determine XFEL pulse widths was investigated theoretically and experimentally. It has been shown that the present system can determine pulse widths from sub-fs to ps in a single shot even for spontaneous radiation. The system can be easily extended to even shorter pulses.Makina Yabashi, Jerome B. Hastings, Max S. Zolotorev, Hidekazu Mimura, Hirokatsu Yumoto, Satoshi Matsuyama, Kazuto Yamauchi, and Tetsuya Ishikawa. Phys. Rev. Lett. 97(8), 084802 (2006)

HIGH-RESOLUTION SEEDING MONOCHROMATOR DESIGN FOR NGLS *

Abstract A high-resolution soft X-ray monochromator system is designed for self-seeding the next generation FEL sources. It consists of a single variable-line-spacing (VLS) grating, an exit slit, and pre-and collimating mirrors, and operates in the fixed-focus mode to achieve complete tuning of the seeding energy from 200 to 2000 eV with a nearly constant resolving power of greater than 50000, producing transform-limited seed ranging from 1 ps at 200 eV to 100 fs at 2000 eV. The optical delay is of order 1 ps, matching well with that of an electron chicane of moderate magnetic field strength. The design is based on a coherent Gaussian beam treatment of the FEL beam propagating from the upstream SASE undulator through the entire seeding monochromator system, preserving the transverse beam profile entering the downstream seeding undulator to ensure maximum coupling efficiency with the reentrant electron beam

Femtosecond photodissociation dynamics of 1,4-diiodobenzene by gas-phase X-ray scattering and photoelectron spectroscopy

We present a multifaceted investigation into the initial photodissociation dynamics of 1,4-diiodobenzene (DIB) following absorption of 267 nm radiation. We combine ultrafast time-resolved photoelectron spectroscopy and X-ray scattering experiments performed at the Linac Coherent Light Source (LCLS) to study the initial electronic excitation and subsequent rotational alignment, and interpret the experiments in light of Complete Active Space Self-Consistent Field (CASSCF) calculations of the excited electronic landscape. The initially excited state is found to be a bound 1B1 surface, which undergoes ultrafast population transfer to a nearby state in 35 ± 10 fs. The internal conversion most likely leads to one or more singlet repulsive surfaces that initiate the dissociation. This initial study is an essential and prerequisite component of a comprehensive study of the complete photodissociation pathway(s) of DIB at 267 nm. Assignment of the initially excited electronic state as a bound state identifies the mechanism as predissociative, and measurement of its lifetime establishes the time between excitation and initiation of dissociation, which is crucial for direct comparison of photoelectron and scattering experiments.</p

Generation of broad spectral components from midwave infrared ultrashort pulse laser propagation through ZnSe and ZnS

We investigate the nonlinear optical properties of ZnSe and ZnS using ultrashort (pulse duration approximately 200 fs) midwave infrared laser pulses between 3 and 4 mu m. Multiple harmonic generation in both materials was observed, as well as significant spectral modification of the fundamental pulse. Simulations using a nonlinear polarization model enhanced with ionization compared favorably with experimental data. Random quasi phase matching in the materials is the likely generator of the observed harmonics.SURVICE [S17-095008/DOTC-17-01-INIT0086]; Air Force Office of Scientific Research (AFOSR) [FA9550-16-1-0069]; AFOSR multidisciplinary research program of the university research initiative (MURI) [FA9550-16-1-0013]; AFOSR [FA9550-16-1-0121]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Scientific Opportunities with an X-ray Free-Electron Laser Oscillator

An X-ray free-electron laser oscillator (XFELO) is a new type of hard X-ray source that would produce fully coherent pulses with meV bandwidth and stable intensity. The XFELO complements existing sources based on self-amplified spontaneous emission (SASE) from high-gain X-ray free-electron lasers (XFEL) that produce ultra-short pulses with broad-band chaotic spectra. This report is based on discussions of scientific opportunities enabled by an XFELO during a workshop held at SLAC on June 29 - July 1, 2016Comment: 21 pages, 12 figure

Imaging Shock Waves in Diamond with Both High Temporal and Spatial Resolution at an XFEL

The advent of hard x-ray free-electron lasers (XFELs) has opened up a variety of scientific opportunities in areas as diverse as atomic physics, plasma physics, nonlinear optics in the x-ray range and protein crystallography. In this article, we access a new field of science by measuring quantitatively the local bulk properties and dynamics of matter under extreme conditions, in this case by using the short XFEL pulse to image an elastic compression wave in diamond. The elastic wave was initiated by an intense optical laser pulse and was imaged at different delay times after the optical pump pulse using magnified x-ray phase-contrast imaging. The temporal evolution of the shock wave can be monitored, yielding detailed information on shock dynamics, such as the shock velocity, the shock front width and the local compression of the material. The method provides a quantitative perspective on the state of matter in extreme conditions

Anomalous nonlinear X-ray Compton scattering

X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electron lasers, nonlinearities can become important, and the probe may no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-ray–matter interactions: the concerted nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4 × 1020 W cm−2, corresponding to an electric field well above the atomic unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical field. We measure a signal from solid beryllium that scales quadratically in intensity, consistent with simultaneous non-resonant two-photon scattering from nearly-free electrons. The high-energy photons show an anomalously large redshift that is incompatible with a free-electron approximation for the ground-state electron distribution, suggesting an enhanced nonlinearity for scattering at large momentum transfer