Soft X-ray harmonic comb from relativistic electron spikes

We demonstrate a new high-order harmonic generation mechanism reaching the `water window' spectral region in experiments with multi-terawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving uJ/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations

Coulomb implosion mechanism of negative ion acceleration in laser plasmas

Coulomb implosion mechanism of the negatively charged ion acceleration in laser plasmas is proposed. When a cluster target is irradiated by an intense laser pulse and the Coulomb explosion of positively charged ions occurs, the negative ions are accelerated inward. The maximum energy of negative ions is several times lower than that of positive ions. The theoretical description and Particle-in-Cell simulation of the Coulomb implosion mechanism and the evidence of the negative ion acceleration in the experiments on the high intensity laser pulse interaction with the cluster targets are presented.Comment: 4 page

Atomic resolution structure of serine protease proteinase K at ambient temperature

Atomic resolution structures (beyond 1.20 ?) at ambient temperature, which is usually hampered by the radiation damage in synchrotron X-ray crystallography (SRX), will add to our understanding of the structure-function relationships of enzymes. Serial femtosecond crystallography (SFX) has attracted surging interest by providing a route to bypass such challenges. Yet the progress on atomic resolution analysis with SFX has been rather slow. In this report, we describe the 1.20 ? resolution structure of proteinase K using 13 keV photon energy. Hydrogen atoms, water molecules, and a number of alternative side-chain conformations have been resolved. The increase in the value of B-factor in SFX suggests that the residues and water molecules adjacent to active sites were flexible and exhibited dynamic motions at specific substrate-recognition sites. ? 2017 The Author(s).114Ysciescopu

Hydroxyethyl cellulose matrix applied to serial crystallography

Serial femtosecond crystallography (SFX) allows structures of proteins to be determined at room temperature with minimal radiation damage. A highly viscous matrix acts as a crystal carrier for serial sample loading at a low flow rate that enables the determination of the structure, while requiring consumption of less than 1 mg of the sample. However, a reliable and versatile carrier matrix for a wide variety of protein samples is still elusive. Here we introduce a hydroxyethyl cellulose-matrix carrier, to determine the structure of three proteins. The de novo structure determination of proteinase K from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of the praseodymium atom was demonstrated using 3,000 diffraction images. ? 2017 The Author(s).113Ysciescopu

Single-shot 3D coherent diffractive imaging of core-shell nanoparticles with elemental specificity

We report 3D coherent diffractive imaging (CDI) of Au/Pd core-shell nanoparticles with 6.1 nm spatial resolution with elemental specificity. We measured single-shot diffraction patterns of the nanoparticles using intense x-ray free electron laser pulses. By exploiting the curvature of the Ewald sphere and the symmetry of the nanoparticle, we reconstructed the 3D electron density of 34 core-shell structures from these diffraction patterns. To extract 3D structural information beyond the diffraction signal, we implemented a super-resolution technique by taking advantage of CDI's quantitative reconstruction capabilities. We used high-resolution model fitting to determine the Au core size and the Pd shell thickness to be 65.0 +/- 1.0 nm and 4.0 +/- 0.5 nm, respectively. We also identified the 3D elemental distribution inside the nanoparticles with an accuracy of 3%. To further examine the model fitting procedure, we simulated noisy diffraction patterns from a Au/Pd core-shell model and a solid Au model and confirmed the validity of the method. We anticipate this super-resolution CDI method can be generally used for quantitative 3D imaging of symmetrical nanostructures with elemental specificity.111Ysciescopu

High order harmonics from relativistic electron spikes

A new regime of relativistic high-order harmonic generation is discovered [Phys. Rev. Lett. 108, 135004 (2012)]. Multi-terawatt relativistic-irradiance (>1018 W/cm2) femtosecond (~30-50 fs) lasers focused to underdense (few×1019 cm-3) plasma formed in gas jet targets produce comb-like spectra with hundreds of even and odd harmonic orders reaching the photon energy of 360 eV, including the 'water window' spectral range. Harmonics are generated by either linearly or circularly polarized pulses from the J-KAREN (KPSI, JAEA) and Astra Gemini (CLF, RAL, UK) lasers. The photon number scalability has been demonstrated with a 120 TW laser producing 40 μJ/sr per harmonic at 120 eV. The experimental results are explained using particle-in-cell (PIC) simulations and catastrophe theory. A new mechanism of harmonic generation by sharp, structurally stable, oscillating electron spikes at the joint of boundaries of wake and bow waves excited by a laser pulse is introduced. In this paper detailed descriptions of the experiments, simulations and model are provided and new features are shown, including data obtained with a two-channel spectrograph, harmonic generation by circularly polarized laser pulses and angular distribution

Characterizing crystalline defects in single Xe nanoparticles from angular correlations of single-shot diffracted X-rays

We performed a wide-angle X-ray scattering experiment of single Xe nanoparticles using an X-ray free electron laser. We developed a novel analysis method that focuses on the angular correlation between plural Bragg spots in single-shot diffraction patterns. The angular correlations of the Bragg spots encode rich structural information and offer an evidence of twinning and stacking faults in Xe nanoparticles.</p

Oil-free hyaluronic acid matrix for serial femtosecond crystallography

The grease matrix was originally introduced as a microcrystal-carrier for serial femtosecond crystallography and has been expanded to applications for various types of proteins, including membrane proteins. However, the grease-based matrix has limited application for oil-sensitive proteins. Here we introduce a grease-free, water-based hyaluronic acid matrix. Applications for proteinase K and lysozyme proteins were able to produce electron density maps at 2.3-angstrom resolution.open111011sciescopu