X-ray Laser Research Articles

John C. H. Spence and the Age of X-Ray Lasers

John C. H. Spence and the Age of X-Ray Lasers

A faster, brighter X-ray laser

A faster, brighter X-ray laser

This X-ray laser is getting faster and brighter

This X-ray laser is getting faster and brighter

Influence of the calcium orthophosphate:glass ratio and calcium orthophosphate functionalization on the degree of conversion and mechanical properties of resin-based composites.

The study verified the influence of calcium orthophosphate (CaP):glass ratio on the degree of conversion and mechanical properties of resin-based composites containing either TEGDMA-functionalized dicalcium phosphate anhydrous (DCPA) or non-functionalized DCPA particles. The null hypotheses were that the evaluated variables are not affected by (1) CaP:glass ratio or (2) DCPA functionalization. DCPA particles were synthesized and half of them were functionalized with TEGDMA. Particle characterization included x-ray diffraction, elemental analysis, laser scattering, helium picnometry and scanning electron microscopy. Two series of composites were prepared containing either DCPA-NF (non-functionalized) or DCPA-F (functionalized), with total inorganic content of 50 vol % and DCPA:silanized barium glass (BG) ratios from 10:40 to 50:0. A composite containing 50 vol % BG was tested as control. DC was determined using FTIR spectroscopy. Biaxial flexural strength and modulus were tested after 24 h in water. Data were analyzed using Kruskal-Wallis/Dunn (flexural properties) or analysis of variance/Tukey tests (DC). Materials with similar actual DCPA contents were compared using Student's t test (alpha: 0.05). DC was higher for materials with DCPA-F, except for the 10:40 ratio. DCPA-F resulted in higher strength than DCPA-NF only at 40:10 ratio. Modulus was not affected by functionalization. Materials with similar actual DCPA contents showed differences in DC (F > NF), while no difference in flexural properties was observed between materials with 28%-30% DCPA. Both null hypotheses were rejected.

Femtosecond soft x-ray lasing in dense collisionaly-pumped plasma

We report the first experimental measurement of a strong pulse shortening of a seeded plasma-based soft x-ray laser at high electron densities. As a consequence of the gain gating caused by subsequent collisional ionization, the duration drops from 1.4 ps to an unprecedented value of 520 fs RMS when the electron density increases from 4 to 7.6×1019cm−3. These measurements, performed with an original single-shot method, are in good agreement with results from 3D Maxwell-Bloch simulations.Received 4 April 2022Accepted 8 June 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L032009Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLaser-plasma interactionsPlasma-beam interactionsRadiation & particle generation in plasmasX-ray generation in plasmasPlasma Physics

Coherent and ultrashort soft x-ray pulses from echo-enabled harmonic cascade free-electron lasers

It is a long-standing challenge for laser technologies to generate intense fully coherent pulses in the x-ray regime. Here, we demonstrate an external seeding mechanism, termed echo-enabled harmonic cascade (EEHC) for generating coherent and ultrashort soft x-ray pulses. The mechanism uses echo-enabled harmonic generation as the first stage, producing intense extreme ultraviolet pulses that seed the second stage x-ray free-electron laser (FEL) with the high-gain harmonic generation setup. Benefiting from the low sensitivity to electron-beam imperfections of EEHC, we generated high-power nearly transform-limited soft x-ray pulses. We have also demonstrated a unique feature of EEHC in generating isolated few-femtosecond-long x-ray pulses. The supreme up-frequency conversion efficiency and flexible pulse length control of this EEHC mechanism allow us to exceed the current limitations of seeded FELs while preserving the coherence of the seed. Our results are a step towards fully coherent and ultrashort x-ray lasers and could enable the extension of nonlinear optical techniques to shorter wavelengths.

Delayed Onset and Directionality of X-Ray-Induced Atomic Displacements Observed on Subatomic Length Scales.

Transient structural changes of Al_{2}O_{3} on subatomic length scales following irradiation with an intense x-ray laser pulse (photon energy: 8.70keV; pulse duration: 6fs; fluence: 8×10^{2} J/cm^{2}) have been investigated by using an x-ray pump x-ray probe technique. The measurement reveals that aluminum and oxygen atoms remain in their original positions by ∼20 fs after the intensity maximum of the pump pulse, followed by directional atomic displacements at the fixed unit cell parameters. By comparing the experimental results and theoretical simulations, we interpret that electron excitation and relaxation triggered by the pump pulse modify the potential energy surface and drives the directional atomic displacements. Our results indicate that high-resolution x-ray structural analysis with the accuracy of 0.01Å is feasible even with intense x-ray pulses by making the pulse duration shorter than the timescale needed to complete electron excitation and relaxation processes, which usually take up to a few tens of femtoseconds.

Measurement of Low-Pressure Plasma Parameters by the Floating Double Probe Method for Dry Air and Helium Gas in a Capillary Glow Discharge

The electrical continuous glow discharge is in the capillary tubes. It has gained great interest especially in the applications of liquid crystals as well as display plasmas and soft x-ray lasers. In the present work, an electrical discharge system was designed consisting of a capillary tube and two electrodes. The cathode takes on a hollow geometric shape from nickel material to obtain a high current density. The anode electrode is a tungsten material. The inter-electrodes distance was taken as 12 cm. The floating Langmuir double probe was used as a diagnostic Tool to measure the plasma parameters at different ranges of gas pressure for dry air and helium as working gases. The current-voltage characteristics of the double probe were measured at gas pressure 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 torr. All measurements are conducted at a constant power of 0.6 watt. Electron temperature and ion saturation current were extracted from the I-V characteristics curves. The electron density, Debye length, and plasma frequency were calculated. It was observed that the electron temperature decreases with increasing working gas pressure. The influence of pressure on electron density and ion saturation current gave a clear similarity to the variation in them with pressure in both gases used. Comparisons of the effect of pressure on plasma parameters in working gases were illustrated. The results were in reasonable agreement with previous research.

Origin of the anomalous properties in supercooled water based on experimental probing inside “no-man's land”

Austen Angell conducted pioneering work that opened up the field of supercooled water by observing the temperature dependent divergence of the thermodynamic response functions. Many different scenarios have been proposed as the origin of the anomalous properties and now it has become possible to test the various hypotheses in experimental studies of bulk supercooled water at conditions where ice crystallization becomes extremely rapid. Through the usage of x-ray lasers, ultrafast measurements could be conducted, as the sample is rapidly brought to the extreme conditions on time scales preceding ice formation. In particular the experimental observation of the existence of a liquid-liquid transition at positive pressure, one phase behavior at atmospheric conditions at temperatures down to 228 K, and the existence of maxima in several properties at 230 K indicative of a Widom line, are only consistent with the proposed liquid-liquid critical point model as the origin of the anomalous properties. • Unexpected behavior of the heat capacity started the field of supercooled water. • Experimental exploration of no-man's land tests hypotheses. • The liquid-liquid transition and critical point scenario consistent with the data.

Femtosecond X-ray Laser Reveals Intact Sea-Island Structures of Metastable Solid-State Electrolytes for Batteries.

Experimental characterization of the nanostructure of metastable functional materials has attracted significant attention with recent advances in computational materials discovery. However, since metastable glass-ceramics are easily damaged by irradiation, damage-free nanoimaging has not been realized thus far. Herein, we propose novel high-contrast coherent diffractive imaging that quantitatively analyzes the intact internal nanostructure of metastable glass-ceramics using femtosecond X-ray pulses. The immersion of sample particles in a solvent helps enhance the reconstructed image contrast and allows us to distinguish an ∼7% electron density difference between an amorphous form and crystals. Furthermore, morphological operations with a band-pass filter quantitatively elucidate the depth information. The evaluated volume ratio of the amorphous to crystalline phases is ∼2.5:1 for the measured metastable (Li2S)70-(P2S5)30 glass-ceramic particle. Sulfide glass-ceramics are used as electrolytes for all-solid-state batteries, which are indispensable for reducing the carbon footprint. Our results will facilitate structural studies on fragile metastable materials with important scientific and industrial implications.

Probing electron and hole colocalization by resonant four-wave mixing spectroscopy in the extreme ultraviolet.

Extending nonlinear spectroscopic techniques into the x-ray domain promises unique insight into photoexcited charge dynamics, which are of fundamental and applied interest. We report on the observation of a third-order nonlinear process in lithium fluoride (LiF) at a free-electron laser. Exploring the yield of four-wave mixing (FWM) in resonance with transitions to strongly localized core exciton states versus delocalized Bloch states, we find resonant FWM to be a sensitive probe for the degree of charge localization: Substantial sum- and difference-frequency generation is observed exclusively when in a one- or three-photon resonance with a LiF core exciton, with a dipole forbidden transition affecting details of the nonlinear response. Our reflective geometry–based approach to detect FWM signals enables the study of a wide variety of condensed matter sample systems, provides atomic selectivity via resonant transitions, and can be easily scaled to shorter wavelengths at free-electron x-ray lasers.

Scanning high-sensitive x-ray polarization microscopy

We report on the realization of an extremely sensitive x-ray polarization microscope, allowing to detect tiniest polarization changes of 1 in 100 billion (10−11) with a μm-size focused beam. The extreme degree of polarization purity places the most stringent requirements on the orientation of the polarizer and analyzer crystals as well as the composition and the form fidelity of the lenses, which must not exhibit any birefringence. The results show that these requirements are currently only met by polymer lenses. Highly sensitive scanning x-ray polarization microscopy thus is established as a new method. It can provide new insights in a wide range of applications ranging from quantum electrodynamics and quantum optics to x-ray spectroscopy, materials research, and laser physics.

LCLS-II helium cryoplant and cryo distribution system installation

The helium cryoplant and cryo distribution system (CDS) are key elements of the new superconducting Linac Coherent Light Source (LCLS-II) and will provide superfluid helium to the accelerator. The cryoplant consists of two helium refrigerators with an equivalent 4.5 K refrigeration capacity of 18 kW each. The 37 cryomodules of the LINAC will be operated at a temperature of 2.0 K to accelerate a 4 GeV electron beam that will generate extremely bright X-ray laser light. Two five-stage cold compressor cold boxes will be utilized to provide superfluid helium II for the superconducting cavity structures with a total cooling capacity of 8 kW at 2.0 K. This paper describes the installation of the LCLS-II cryoplant and CDS. The LCLS-II cryoplant was designed and contributed by Jefferson Lab. To expedite the project completion the reuse of proven design and technology from the Jefferson Lab CHL-2 cryoplant was the preferred strategy. The CDS consists of ∼260 m thermally shielded and vacuum super insulated transfer lines, two distribution boxes and eight feed and end caps, and was designed and contributed by Fermilab. SLAC installed the cryoplant components into a newly erected building and the CDS components into the existing accelerator tunnel and klystron gallery with strong engineering support from both partner labs.

LCLS-II warm helium compressor commissioning

LCLS-II is major up-grade to the SLAC Facility. It adds a 4 GeV superconducting accelerator, which will generate an extremely bright and continuous (million pulses/sec) X-ray laser beam. The LCLS-II superconducting accelerator comprises 37 cryomodules connected through a complex distribution system to two large Helium Refrigerators. A single Helium cryogenic plant is expected to deliver 4.0 kW of cooling capacity at 2.0 K. Each cryogenic plant has a set of five operating compressors with an additional spare compressor that provides the required mechanical power (∼ 4.5 MW / cryogenic plant). In this paper, we describe the recent commissioning and performance test results of the LCLS-II compressor system.

Amplification of elliptically polarized sub-femtosecond pulses in neon-like X-ray laser modulated by an IR field

Amplification of attosecond pulses produced via high harmonic generation is a formidable problem since none of the amplifiers can support the corresponding PHz bandwidth. Producing the well defined polarization state common for a set of harmonics required for formation of the circularly/elliptically polarized attosecond pulses (which are on demand for dynamical imaging and coherent control of the spin flip processes) is another big challenge. In this work we show how both problems can be tackled simultaneously on the basis of the same platform, namely, the plasma-based X-ray amplifier whose resonant transition frequency is modulated by an infrared field.

Temporal @ spatial anti-counterfeiting with Mn2+/Bi3+/Er3+ doped BaZnOS phosphors

Fluorescent materials have been employed in the field of anti-counterfeiting thanks to their feasible and flexible design approach, visualization feature, and handy identification. However, versatile fluorescent materials are still eager to be developed for advanced information security. Here, an efficient temporal and spatial anti-counterfeiting strategy is proposed with the multi-response behaviors from the as-explored transition metal and lanthanide ions doped BaZnOS phosphors under distinct stimulus. Diverse optical performance of the corresponding phosphor with the irradiation of X-ray, ultraviolet (UV), and near-infrared laser as well as the stimulation of stress and temperature endows a spatial anti-counterfeiting strategy. Moreover, with the cooperation of the photo-stimulated and up-conversion behaviors, a temporal anti-counterfeiting could be achieved elaborately. Herein, this work not only gives an insight to understand the multi-dimensional response of the corresponding tailored phosphor under distinct exterior stimulations, but also provides a feasible and facilitated way to address the counterfeit issues accordingly.

FIB-DIC Residual Stress Evaluation in Shot Peened VT6 Alloy Validated by X-ray Diffraction and Laser Speckle Interferometry.

Ga-ion micro-ring-core FIB-DIC evaluation of residual stresses in shot peened VT6 (Ti-6Al-4V) alloy was carried out and cross-validated against other non-destructive and semi-destructive residual stresses evaluation techniques, namely, the conventional X-ray diffraction and mechanical hole drilling. The Korsunsky FIB-DIC method of Ga-ion beam micro-ring-core milling within FIB-SEM with Digital Image Correlation (DIC) deformation analysis delivered spatial resolution down to a few micrometers, while the mechanical drilling of circular holes of ~2 mm diameter with laser speckle interferometry monitoring of strains gave a rough spatial resolution of a few millimeters. Good agreement was also found with the X-ray diffraction estimates of residual stress variation profiles as a function of depth. These results demonstrate that FIB-DIC provides rich information down to the micron scale, it also allows reliable estimation of macro-scale residual stresses.

Hard x-ray intensity autocorrelation using direct two-photon absorption

The authors show a direct characterization of 9-keV x-ray laser pulse duration and find that temporal shapes of fluctuating ultrashort x-ray pulses can be tailored through Bragg diffraction in perfect crystals.

Asymmetric electron angular distributions in H2 induced by intense ultrashort soft-x-ray laser pulses

The authors report a theoretical study on the process of stimulated Compton scattering in the close-to-threshold ionization of the hydrogen molecule with x-ray attosecond radiation by solving the time-dependent Schr\"odinger equation with nondipole corrections. They show how to control and isolate the nondipole-induced nonlinear photoelectron emission by adjusting the x-ray laser parameters and molecular alignment.

Tattoo Pigment Identification in Inks and Skin Biopsies of Adverse Reactions by Complementary Elemental and Molecular Bioimaging with Mass Spectral Library Matching.

Tattooing has become increasingly popular throughout society. Despite the recognized issue of adverse reactions in tattoos, regulations remain challenging with limited data available and a missing positive list. The diverse chemical properties of mostly insoluble inorganic and organic pigments pose an outstanding analytical challenge, which typically requires extensive sample preparation. Here, we present a multimodal bioimaging approach combining micro X-ray fluorescence (μXRF) and laser desorption ionization-mass spectrometry (LDI-MS) to detect the elemental and molecular composition in the same sample. The pigment structures directly absorb the laser energy, eliminating the need for matrix application. A computational data processing workflow clusters spatially resolved LDI-MS scans to merge redundant information into consensus spectra, which are then matched against new open mass spectral libraries of tattoo pigments. When applied to 13 tattoo inks and 68 skin samples from skin biopsies in adverse tattoo reactions, characteristic signal patterns of isotopes, ion adducts, and in-source fragments in LDI-MS1 scans yielded confident compound annotations across various pigment classes. Combined with μXRF, pigment annotations were achieved for all skin samples with 14 unique structures and 2 inorganic pigments, emphasizing the applicability to larger studies. The tattoo-specific spectral libraries and further information are available on the tattoo-analysis.github.io website.