X-ray Laser Radiation Research Articles

New approaches in the tomographic visualization of joints using X-ray contrast nanoparticles and laser radiation

New approaches in the tomographic visualization of joints using X-ray contrast nanoparticles and laser radiation

New Approaches in the Tomographic Visualization of Joints Using X-ray Contrast Nanoparticles and Laser Radiation

New Approaches in the Tomographic Visualization of Joints Using X-ray Contrast Nanoparticles and Laser Radiation

Microscopic Kinetics in Poly(Methyl Methacrylate) Exposed to a Single Ultra-Short XUV/X-ray Laser Pulse.

We study the behavior of poly(methyl methacrylate) (PMMA) exposed to femtosecond pulses of extreme ultraviolet and X-ray laser radiation in the single-shot damage regime. The employed microscopic simulation traces induced electron cascades, the thermal energy exchange of electrons with atoms, nonthermal modification of the interatomic potential, and a triggered atomic response. We identify that the nonthermal hydrogen decoupling triggers ultrafast fragmentation of PMMA strains at the absorbed threshold dose of ~0.07 eV/atom. At higher doses, more hydrogen atoms detach from their parental molecules, which, at the dose of ~0.5 eV/atom, leads to a complete separation of hydrogens from carbon and oxygen atoms and fragmentation of MMA molecules. At the dose of ~0.7 eV/atom, the band gap completely collapses indicating that a metallic liquid is formed with complete atomic disorder. An estimated single-shot ablation threshold and a crater depth as functions of fluence agree well with the experimental data collected.

Abstract P-5: Neural Network Approaches to Classify 3D Protein Structures from the Data of X-ray Laser Radiation Diffraction from Single Particles

Background: Protein structure determination using X-ray free-electron laser (XFEL) includes analysis and merging a large number of snapshot diffraction patterns. Convolutional neural networks are widely used to solve numerous computer vision problems, e.g. image classification, and can be used for diffraction pattern analysis. But the task of protein structure determination with the use of CNNs only is not yet solved. Methods: We simulated the diffraction patterns using the Condor software library and obtained more than 1000 diffraction patterns for each structure with simulation parameters resembling real ones. To classify diffraction patterns, we tried two approaches, which are widely known in the area of image classification: a classic VGG network and residual networks. Results: 1. Recognition of a protein class (GPCRs vs globins). Globins and GPCR-like proteins are typical α-helical proteins. Each of these protein families has a large number of representatives (including those with known structure) but we used only 8 structures from every family. 12,000 of diffraction patterns were used for training and 4,000 patterns for testing. Results indicate that all considered networks are able to recognize the protein family type with high accuracy. 2. Recognition of the number of protein molecules in the liposome. We considered the usage of lyposomes as carriers of membrane or globular proteins for sample delivery in XFEL experiments in order to improve the X-ray beam hit rate. Three sets of diffractograms for liposomes of various radius were calculated, including diffractograms for empty liposomes, liposomes loaded with 5 bacteriorhodopsin molecules, and liposomes loaded with 10 bacteriorhodopsin molecules. The training set consisted of 23625 diffraction patterns, and test set of 7875 patterns. We found that all networks used in our study were able to identify the number of protein molecules in liposomes independent of the liposome radius. Our findings make this approach rather promising for the usage of liposomes as protein carriers in XFEL experiments. Conclusion: Thus, the performed numerical experiments show that the use of neural network algorithms for the recognition of diffraction images from single macromolecular particles makes it possible to determine changes in the structure at the angstrom scale.

Femtosecond X-ray Lasers at λ=32.8 and 44.4 nm in a Plasma Formed by Optical Field Ionization in a Krypton Cluster Jet

Due to high efficiency, X-ray lasers based on transitions of Ni-like krypton (Kr⁸⁺) are being actively studied. The main focus is on an X-ray laser based on the conventional 3d_5/24d_5/2 [J=0] – 3d_3/24p_1/2 [J=1] transition at λ=32.8 nm. Gaseous krypton targets or krypton cluster jets are used in various experiments. X-ray lasers at 32.8 nm in a plasma formed by optical field ionization in a krypton cluster jet are widely used for research of nanoobjects. In this article, the possibility of creating an efficient X-ray laser in Ni-like krypton based on a transition with optical self-pumping 3d_3/24f_5/2 [J=1] – 3d_3/24d_5/2 [J=1] at λ=44.4 nm is predicted for the first time. The plasma filament is excited upon interaction of a jet of krypton clusters with an intense pump laser pulse. Optimal conditions to achieve the duration t_las ≤300 fs of the X-ray laser radiation are determined. The optimal electron density is in a rather narrow interval in the range n_e ~ 10²¹ - 2×10²¹ cm^-3. The optimal electron temperature is several keV. It is likely that this explains the fact that no X-ray laser has been observed on this transition in Kr⁸⁺ so far. The conversion factor per pulse is found to be ~5×10^-5. For an X-ray laser operating on the conventional transition 3d_5/24d_5/2 [J=0] – 3d_3/24p_1/2 [J=1] at λ=32.8 nm, t_las ≤ 300 fs can also be achieved; however, the conversion factor for this transition is times ~5 smaller than that for the former transition.

The Influence of X-ray and UV Laser Radiation on the Optical Properties of Alkali-Containing Silicate Glasses

The results of complex action of X-ray and nanosecond UV laser radiation on alkali-containing silicate glasses are presented. It is shown that X-ray irradiation of glasses forms luminescent color centers in them, which is related to increasing concentration of structural defects in glass network. Laser radiation destroys these defects, which is accompanied by bleaching of glasses and disappearance of luminescence in irradiated regions. The dynamics of glass bleaching under action of laser radiation and the influence of alkali-metal (Li, Na, K) ions on this process are studied. Mechanisms of destruction of color centers by laser radiation are proposed.

Generation of Coherent Radiation in the Near X-Ray Band by a Cascade FEL with a Two-Frequency Undulator

Generation of X-ray radiation in a cascade self-amplified spontaneous emission free-electron laser (SASE FEL) using the harmonics of a two-frequency undulator is studied. The advanced phenomenological model of a one-pass FEL that accounts for the main losses in real FELs is presented: the electron energy spread in the beam, the beam divergence, diffraction, and the fact that emission losses are greater at higher harmonics than in the main frequency range. The FEL mathematical model was performed using the Mathematica software and calibrated within the experiment carried out at the operating SPARC facility via complex three-dimensional numerical simulations. The phenomenological model is used to analyze FEL dynamics for generation of a high-energy X-ray emission at a relatively short length. It is proposed to use a two-frequency undulator for the initial electron grouping and subsequent frequency multiplication in a cascade FEL with higher harmonic amplification (HGHG). The advantages of the two-frequency undulator are presented for electron grouping at higher harmonics of the undulator radiation (UR). The operation of several types of FEL is simulated with amplification of the seed laser wave frequency in two and three cascades to generate the soft X-ray radiation. A seed laser with a wavelength of 11.43 nm corresponding to the peak reflectivity of mirror coatings with MoRu/Be is proposed for generating the intensive X-ray laser radiation with λ ~ 1.27–3.37 nm. Here, the intensive radiation power reaches 50 MW at a length of only 35 meters; the radiation shows good temporal coherence corresponding to the performance of a low-power seed laser with a lower frequency.

Multicascade X-Ray Free-Electron Laser with Harmonic Multiplier and Two-Frequency Undulator

The feasibility of generation of powerful x-ray radiation by a cascade free-electron laser (FEL) with amplification of higher harmonics using a two-frequency undulator is studied. To analyze the FEL operation, a complex phenomenological single-pass FEL model is developed and used. It describes linear and nonlinear generation of harmonics in the FEL with seed laser that takes into account initial electron beam noise and describes all main losses of each harmonic in each FEL cascade. The model is also calibrated against and approved by the experimental FEL data and available results of three-dimensional numerical simulation. The electron beam in the undulator is assumed to be matched and focused, and the dynamics of power in the singlepass FEL with cascade harmonic multipliers is investigated to obtain x-ray laser radiation in the FEL having the shortest length, beam energy, and frequency of the seed laser as low as possible. In this context, the advantages of the two-frequency undulator used for generation of harmonics are demonstrated. The evolution of harmonics in a multicascade FEL with multiplication of harmonics is investigated. The operation of the cascade FEL at the wavelength λ = 1.14 nm, generating ~30 MW already on 38 m with the seed laser operating at a wavelength of 11.43 nm corresponding to the maximal reflectivity of the multilayered mirror MoRu/Be coating is investigated. In addition, the operation of the multicascade FEL with accessible seed UVlaser operating at a wavelength of 157 nm (F2 excimer UV-laser) and electron beam with energy of ~0.5 GeV is investigated. X-ray radiation simulated in it at the wavelength λ ~ 3.9 nm reaches power of ~50 MW already at ~27 m, which is by two orders of magnitude shorter than 3.4 km of the x-ray FEL recently put into operation in Europe.

Defining experimental geometry to determine wave properties of X-ray laser radiation by the diffraction method

Defining experimental geometry to determine wave properties of X-ray laser radiation by the diffraction method

Saturation of a Ce:Y_3Al_5O_12 scintillator response to ultra-short pulses of extreme ultraviolet soft X-ray and X-ray laser radiation

Investigations of radioluminescence saturation in monocrystalline cerium doped yttrium aluminum garnet (Ce:YAG) exposed to intense extreme ultraviolet (XUV), soft X-ray and X-ray radiation delivered from three free-electron lasers are described in this article. The measurements were performed with wavelengths of 98, 25.6, 13.5 and 0.15 nm. We have found that saturation of the photon yield occurs at an excitation level of 2.0 x 1020 eV/cm3 resulting in an emission of 1.5 x 1018 visible photons per cubic centimeter. This number is much smaller than the concentration of Ce3+ in the scintillator that was equal to 2 x 1020 cm−3. Because the internal radiance efficiency η does not depend strongly on the irradiating photon energy, i.e., η ≈0.035 ± 0.015 in the range 10 to 100 000 eV, the results presented here could be used to predict saturation effects in scintillator slabs placed in imaging systems of bright XUV, X-ray and particle beams. The saturation of the Ce3+ emission is explained by mutual quenching of excitons created at high densities, preceding the stage of energy transfer to the Ce3+ ions.

Soft x-ray free-electron laser induced damage to inorganic scintillators

An irreversible response of inorganic scintillators to intense soft x-ray laser radiation was investigated at the FLASH (Free-electron LASer in Hamburg) facility. Three ionic crystals, namely, Ce:YAG (cerium-doped yttrium aluminum garnet), PbWO4 (lead tungstate), and ZnO (zinc oxide), were exposed to single 4.6 nm ultra-short laser pulses of variable pulse energy (up to 12 μJ) under normal incidence conditions with tight focus. Damaged areas produced with various levels of pulse fluences, were analyzed on the surface of irradiated samples using differential interference contrast (DIC) and atomic force microscopy (AFM). The effective beam area of 22.2 ± 2.2 μm2 was determined by means of the ablation imprints method with the use of poly(methyl methacrylate) - PMMA. Applied to the three inorganic materials, this procedure gave almost the same values of an effective area. The single-shot damage threshold fluence was determined for each of these inorganic materials. The Ce:YAG sample seems to be the most radiation resistant under the given irradiation conditions, its damage threshold was determined to be as high as 660.8 ± 71.2 mJ/cm2. Contrary to that, the PbWO4 sample exhibited the lowest radiation resistance with a threshold fluence of 62.6 ± 11.9 mJ/cm2. The threshold for ZnO was found to be 167.8 ± 30.8 mJ/cm2. Both interaction and material characteristics responsible for the damage threshold difference are discussed in the article.

X-ray lasing in diatomic molecules

We predict high-gain x-ray lasing in diatomic molecules by ultrafast core ionization of the C K- and O K-edges in CO and the N K-edge in N2 with an x-ray free-electron laser source. To estimate the spectral and temporal output of this molecular x-ray laser, we solve generalized Maxwell-Bloch equations, keeping track of the electronic and nuclear degrees of freedom. Despite the broad fluorescence bandwidth, the amplified x-ray emission shows a narrow spectrum. By controlling the molecular alignment and thereby the alignment of the transition dipole moment polarization and emission energy control of the x-ray laser radiation is achievable.

Molecular dynamics with atomic transitions and nuclear reactions

We describe molecular dynamics particle simulations with particles that have internal structure and/or undergo reactions. These calculations give an atomic-scale description of hot plasma based on well-established microphysics and test kinetic theories used to calculate energy exchange and transport in plasma hydrodynamic simulations. The computer experiments can be given detailed diagnostics, without the usual limits of resolution of Laboratory equipment. Typical applications are non-equilibrium atomic kinetics for emission or absorption of X-ray laser radiation by solid targets and/or atomic-scale simulation of hot plasma with fusion reactions, as in inertial fusion ignition experiments.

Single-shot analysis of hard x-ray laser radiation using a noninvasive grating spectrometer

We present a spectrometer setup based on grating dispersion for hard x-ray free-electron lasers. This setup consists of a focusing spectrometer grating and a charge-integrating microstrip detector. Measurement results acquired at Linac Coherent Light Source are presented, demonstrating noninvasive monitoring of single-shot spectra with a resolution of 2.0×10(-4) ±0.3×10(-4) at photon energy of 6 keV with more than 95% transmission of the main beam.

X-ray lasing on the 4d — 4p transitions of Ni-like molybdenum ions

We outline the results of experiments in the generation of X-ray laser radiation on the 4d — 4p Ni-like ion transitions at a wavelength λ = 189 Å under sequential irradiation of plane targets by two laser pulses focused to a line. These experiments were executed on the Sokol-p picosecond laser facility. The average energy of a 4-ps long ultrashort pump pulse was equal to 6.5 J, the energy of a 0.44-ns long prepulse was equal to 2.7 J, and the time delay between them was equal to 1.5 ns. The effective gain for short target lengths was equal to ∼24 cm-1. In the travelling pump wave regime, which was realised using a ladder mirror, we obtained an 8-fold increase in output X-ray laser energy in comparison with the output energy obtained in the ordinary target irradiation regime.

EFFECT OF COMBINED X-RAY AND LASER PULSE RADIATION ON THE PARAMETERS OF SILICON MOS-TRANSISTORS

In this paper the influence of X-ray and pulsed laser (λ = 1,06 мкм, τ =10-3 с) radiation the parameters of silicon MOS-transistors with channel length 1…10 мкм. The results of the observed changes in the parameters are interpreted in the framework of positive integer charge in the bulk dielectric undergate SiO2. And defect-impurity nature of the interphase boundary Si-SiO2 ,the potential relief which undergoes a structural transformation under the influence of X-ray- laser treatment.

Simulations of neon irradiated by intense X-ray laser radiation

We present simulations of the charge states produced by the interaction of intense X-ray laser radiation with a neon gas. We model the results of a recent experiment (Young et al., Nature 466, 56 (2010)), where mJ pulses of X-rays, with photon energies ranging from 800 to 2000 eV and pulse lengths ranging from 70 to 340 fs were incident on neon atoms at intensities of up to 10 18 W cm −2. Simulations using an adapted version of the SCFLY collisional-radiative code, which included the effect of electron collisions and a simple self-consistent temperature model, result in charge state distributions that are in good agreement with the experimental data. We calculate the electron temperature of the system during the evolution of the plasma, and comment upon the role that collisions may play in determining the charge state distributions as a function of the neon ion number density.

XUV and Soft X-Ray Laser Radiation from Ni-Like Au

Atomic structure data and effective collision strengths from literature for 1s2 2s2 2p6 3s2 3p63d10 and 34 fine-structure levels contained in the configurations 1s2 2s2 2p6 3s2 3p63d9 4l (l = s, p, d) for the nickel-like Au ion are used in the determination of the reduced population for these levels over a wide range of electron densities and at various electron plasma temperatures. The gain coefficient for those transitions with positive population inversion factor are determined and plotted against the electron density.

Absolute calibration of X-ray optical elements and detectors at a wavelength of 46.9 nm

The results are presented of the absolute calibration of X-ray optical elements (diffraction gratings and Sc/Si multilayers) and detectors (an УΦ-4 photographic film and a vacuum X-ray diode) used in diagnostic devices to study generation of X-ray laser radiation in an argon plasma of a capillary discharge (λ = 46.9 nm). The measurements have been performed at the soft X-ray and vacuum UV station of the VEPP-4 storage ring at the Siberian International Center of Synchrotron Radiation. An absolutely calibrated AXUV 100G photodiode has been used as a reference detector. The relative error of calibration is 10%. The measured reflectances of the multilayer mirrors and gratings are in good agreement (within the limits of errors) with the results of their calibration at the RKK-1-100 X-ray calibration facility.

Measurements of opacity and temperature of warm dense matter heated by focused soft X-ray laser irradiation

The transmission of plasma-based soft X-ray lasers through thin targets can be used to measure the target opacity. Measurements of warm dense matter transmission obtained using a focused 59 eV photon energy laser irradiation on thin targets of polyimide (C 22H 10N 2O 5) and aluminum are shown to produce simultaneous heating and probing enabling opacity and temperature measurements of warm dense matter. It is shown that the opacity of the warm dense matter considered in the experiments follows closely tabulated cold ‘room temperature’ opacities at temperatures below ∼10 eV. Transmission measurements of thin iron targets which are highly opaque to the X-ray laser radiation are also presented.