Single X-ray Pulse Research Articles

Spin-Polarization Control of Photoelectrons Using Poincaré Fields.

Efficient helicity transfer from Poincaré fields to electrons of hydrogenic ions is revealed for the first time by four-dimensional relativistic simulations. The magnetic multipole class of Poincaré fields is chosen due to its fundamental role in light-matter spin coupling, and the calculation is demonstrated for Ne^{9+} ion irradiated by single and multimode x-ray pulses. Photoelectrons of both helicities emerge synchronously from the ion ensemble, and their directionality is controllable through the radiation mode numbers. The helicity density distributions display novel structures composed of jets, spirals, and rings, among others, that are unique to the combination of atomic and field parameters. Our approach to generate spin-polarized leptons using Poincaré fields may provide a new platform for helicity characterization based on advanced numerical capabilities.

Double diffraction imaging of x-ray induced structural dynamics in single free nanoparticles

Because of their high photon flux, x-ray free-electron lasers (FEL) allow to resolve the structure of individual nanoparticles via coherent diffractive imaging (CDI) within a single x-ray pulse. Since the inevitable rapid destruction of the sample limits the achievable resolution, a thorough understanding of the spatiotemporal evolution of matter on the nanoscale following the irradiation is crucial. We present a technique to track x-ray induced structural changes in time and space by recording two consecutive diffraction patterns of the same single, free-flying nanoparticle, acquired separately on two large-area detectors opposite to each other, thus examining both the initial and evolved particle structure. We demonstrate the method at the extreme ultraviolet (XUV) and soft x-ray Free-electron LASer in Hamburg (FLASH), investigating xenon clusters as model systems. By splitting a single XUV pulse, two diffraction patterns from the same particle can be obtained. For focus intensities of about 2×1012 W cm−2 we observe still largely intact clusters even at the longest delays of up to 650 picoseconds of the second pulse, indicating that in the highly absorbing systems the damage remains confined to one side of the cluster. Instead, in case of five times higher flux, the diffraction patterns show clear signatures of disintegration, namely increased diameters and density fluctuations in the fragmenting clusters. Future improvements to the accessible range of dynamics and time resolution of the approach are discussed.

Real-time structural characterization of protein response to a caged compound by fast detector readout and high-brilliance synchrotron radiation

Protein dynamics are essential to biological function, and methods to determine such structural rearrangements constitute a frontier in structural biology. Synchrotron radiation can track real-time protein dynamics, but accessibility to dedicated high-flux single X-ray pulse time-resolved beamlines is scarce and protein targets amendable to such characterization are limited. These limitations can be alleviated by triggering the reaction by laser-induced activation of a caged compound and probing the structural dynamics by fast-readout detectors. In this work, we established time-resolved X-ray solution scattering (TR-XSS) at the CoSAXS beamline at the MAX IV Laboratory synchrotron. Laser-induced activation of caged ATP initiated phosphoryl transfer in the adenylate kinase (AdK) enzyme, and the reaction was monitored up to 50ms with a 2-ms temporal resolution achieved by the detector readout. The time-resolved structural signal of the protein showed minimal radiation damage effects and excellent agreement to data collected by a single X-ray pulse approach.

Single-Pulse X-ray Acoustic Computed Tomographic Imaging for Precision Radiation Therapy

High-precision radiation therapy is crucial for cancer treatment. Currently, the delivered dose can only be verified via simulations with phantoms, and an in-tumor, online dose verification is still unavailable. An innovative detection method called x-ray-induced acoustic computed tomography (XACT) has recently shown the potential for imaging the delivered radiation dose within the tumor. Prior XACT imaging systems have required tens to hundreds of signal averages to achieve high-quality dose images within the patient, which reduces its real-time capability. Here, we demonstrate that XACT dose images can be reproduced from a single x-ray pulse (4 µs) with sub-mGy sensitivity from a clinical linear accelerator. By immersing an acoustic transducer in a homogeneous medium, it is possible to detect pressure waves generated by the pulsed radiation from a clinical linear accelerator. After rotating the collimator, signals of different angles are obtained to perform a tomographic reconstruction of the dose field. Using 2-stage amplification with further bandpass filtering increases the signal-to-noise ratio (SNR). Acoustic peak SNR and voltage values were recorded for singular and dual-amplifying stages. The SNR for single-pulse mode was able to satisfy the Rose criterion, and the collected signals were able to reconstruct 2-dimensional images from the 2 homogeneous media. By overcoming the low SNR and requirement of signal averaging, single-pulse XACT imaging holds great potential for personalized dose monitoring from each individual pulse during radiation therapy.

Single and multi-pulse based X-ray photon correlation spectroscopy.

The ability of pulsed nature of synchrotron radiation opens up the possibility of studying microsecond dynamics in complex materials via speckle-based techniques. Here, we present the study of measuring the dynamics of a colloidal system by combining single and multiple X-ray pulses of a storage ring. In addition, we apply speckle correlation techniques at various pulse patterns to collect correlation functions from nanoseconds to milliseconds. The obtained sample dynamics from all correlation techniques at different pulse patterns are in very good agreement with the expected dynamics of Brownian motions of silica nanoparticles in water. Our study will pave the way for future pulsed X-ray investigations at various synchrotron X-ray sources using individual X-ray pulse patterns.

Molecular photodissociation dynamics revealed by Coulomb explosion imaging.

Coulomb explosion imaging (CEI) methods are finding ever-growing use as a means of exploring and distinguishing the static stereo-configurations of small quantum systems (molecules, clusters, etc). CEI experiments initiated by ultrafast (femtosecond-duration) laser pulses also allow opportunities to track the time-evolution of molecular structures, and thereby advance understanding of molecular fragmentation processes. This Perspective illustrates two emerging families of dynamical studies. 'One-colour' studies (employing strong field ionisation driven by intense near infrared or single X-ray or extreme ultraviolet laser pulses) afford routes to preparing multiply charged molecular cations and exploring how their fragmentation progresses from valence-dominated to Coulomb-dominated dynamics with increasing charge and how this evolution varies with molecular size and composition. 'Two-colour' studies use one ultrashort laser pulse to create electronically excited neutral molecules (or monocations), whose structural evolution is then probed as a function of pump-probe delay using an ultrafast ionisation pulse along with time and position-sensitive detection methods. This latter type of experiment has the potential to return new insights into not just molecular fragmentation processes but also charge transfer processes between moieties separating with much better defined stereochemical control than in contemporary ion-atom and ion-molecule charge transfer studies.

FLASH Effects Induced by kV X-Rays in a Murine Skin Model

<h3>Purpose/Objective(s)</h3> Current research on FLASH dose rate radiotherapy is predominantly performed with advanced proton or electron accelerators of limited access to the laboratory researcher. Stationary anode orthovoltage x-ray irradiators would be desirable but are currently incapable of supporting the power requirements to operate at FLASH dose rates. In this study, we investigate the use of rotating anode x-ray tubes to overcome these limitations. We present the dosimetric characterization of a rotating anode x-ray system for laboratory FLASH research and its implementation for a pilot study of radiation skin toxicities in mice. <h3>Materials/Methods</h3> A high-capacity rotating anode x-ray tube was installed in our laboratory with a 75-kW generator, operating at 150 kVp with 0.025 mm Cu added filtration. Calibrated radiographic film was irradiated at varying depths in kV solid water to measure output, beam profiles, and depth-dose parameters (PDD). A variety of wild-type mice (GR/GRT, CMV) were irradiated to the hind flank to 38 or 48 Gy at the highest achievable dose rate (FLASH-IR). Conventional dose rate irradiations (CONV-IR) to the same doses were performed at 3 Gy/min using a 220 kVp x-ray irradiator. Visible skin toxicities were assessed weekly and quantified using a skin scoring scale for endpoints of hair loss, erythema, and ulceration (n= 7 per dose at each dose rate). At 8-weeks post irradiation, skin samples were harvested and stained with H&E to assess pathological changes from FLASH-IR or CONV-IR x-rays. <h3>Results</h3> Dose rates peaked at 101 Gy/s in the cathode side of the radiation field from anode heel effects. The total field size at 46 mm SSD was 20 × 20mm². A useable region of 10 × 20 mm² for FLASH studies was defined as the cathode-half of the field, with an average dose rate of 96.1 ± 2.8 Gy/s. The PDD within this region falls to 67% at 5mm depth in solid water and 51% at 10 mm. At 4 weeks post irradiation, CONV-IR mice saw hair loss and erythema in the entire irradiated region, while all FLASH-IR mice retained hair in-field with no change in skin condition. By 8 weeks post irradiation, skin effects in all FLASH-IR mice did not progress beyond hair loss in field, while all CONV-IR mice had progressed to more severe skin toxicities. Pathological assessments are ongoing. Early analysis shows higher frequency of ulceration, dermis hyperplasia, and fibrosis from CONV-IR than FLASH-IR. <h3>Conclusion</h3> This study presents the first observation of FLASH effects induced by a single pulse of kV x-rays in an animal skin toxicity model. FLASH dose rates requisite for preclinical research are achievable with kV x-rays using rotating anode technology. X-ray FLASH effects in skin occur at comparable doses to those published for FLASH electrons and protons. The use of a single x-ray pulse suggests that average dose rate is the necessary condition, in contrast to fine pulse structure, for the induction of FLASH effects.

Experimental studies on the X-ray single-pulse jitter at the SSRF

At the Shanghai Synchrotron Radiation Facility (SSRF), ultrafast experiments require picosecond temporal resolution. Thus, understanding the jitter of a single X-ray pulse is important. In this study, a timing synchronization control system that combines a timing system, optical fiber network, and X-ray streak camera detection system were employed to accurately acquire the temporal characteristics of a single X-ray pulse at a low photon intensity(103 photons/pulse). Experimental results showed that the intensity of a single X-ray pulse is distributed as a Gaussian curve in the longitudinal direction, and the pulse jitter broadens to approximately 5 ps, which is sufficient for ultrafast temporal resolution research at the SSRF.

Unique atomic structure of metals at the moment of fracture induced by laser shock

To effectively control the mechanical properties of structural materials and design their safety margins, understanding the properties of metal fracture is essential. However, it is difficult to experimentally investigate the atomic structures at the moment of fracture; therefore, the detailed fracture mechanism remains an active area of research. In this study, we in situ examined how the atomic structure of copper changes during the fracture process on the nanosecond scale using X-ray absorption spectroscopy and X-ray diffraction. The fracture was triggered by a shock wave induced by an optical laser and was examined with a single 100-ps synchrotron X-ray pulse with a delay time of 0–200 ns. This novel experimental approach provides insights into how the short- and long-range order of an atomic structure change on the nanosecond scale. The results showed that there was an irreversible change in the deformation state on the nanosecond scale. The initial elastic deformation state (0–20 ns) was superseded by a plastic deformation state (20–50 ns). Then, at the moment of fracture (50–320 ns), the plastic deformation state transformed into a state in which the heterogeneous atomic structures exhibited short-range disorder while maintaining long-range order (a “short-range-disorder-only” state). This unique “short-range-disorder-only” state, which has never been reported using conventional ex situ analytical techniques, triggered metal fracture; therefore, controlling the occurrence of this state could suppress fracture and allow the design of reasonable metal safety margins to avoid overengineering.

Data Transmission in the X-Ray Emission Frequency Range of Electromagnetic Radiation

Introduction. Data transmission systems using the X-ray frequency range of electromagnetic radiation – X-ray communication system (XCS) have a number of advantages in comparison with radio or optical communication systems. The most significant advantages for practical use are their higher stealth and external interferences resistance, as well as stability against interception and decryption. It is of importance to develop a method for calculating the main parameters of an X-ray communication system: the range and speed of data transmission. In addition, the construction design and results of experimental research of the current X-ray communication system should be provided.Aim. To develop physical and technical foundations of data transmission systems using the X-ray frequency range of electromagnetic radiation.Materials and methods. We used an original method of calculating the X-ray emission spectrum, taking into account the attenuation coefficient in the propagation medium.Results. A technique for data transmission using the X-ray frequency range of electromagnetic radiation was suggested, including a method for calculating basic parameters e.g. the transmission range and speed, as well as the construction design of the current X-ray communication system model. Relations between these parameters and the operating modes of the X-ray tube were shown. The calculated and experimental data were in good agreement, sufficient for practical use. On their basis, it can be expected that at a voltage across the X-ray tube of 200 kV and the tube current of 1A in a 1-μs pulse, data transmission range in free air will be about 250 m. The maximum possible data transmission rate when using the developed X-ray tube will be 5 Mbit/s.Conclusions. The results of analytical and experimental investigations showed that the range and rate of data transmission of the XCS are exclusively determined by the transmitter energetic capabilities: by voltage and average the X-ray tube current during the generation of packages (series) of the X-ray pulses, as well as by the duration of a single X-ray pulse. It is concluded that the prospects of XCS depend on the development of specialized X-ray sources generating a series of pulses with the minimum possible duration of every single pulse in a series. Taking into account the specific features, XCS can become an alternative to conventional radio and optical systems for communication and navigation.

Electron-ion coincidence measurements of molecular dynamics with intense X-ray pulses

Molecules can sequentially absorb multiple photons when irradiated by an intense X-ray pulse from a free-electron laser. If the time delay between two photoabsorption events can be determined, this enables pump-probe experiments with a single X-ray pulse, where the absorption of the first photon induces electronic and nuclear dynamics that are probed by the absorption of the second photon. Here we show a realization of such a single-pulse X-ray pump-probe scheme on N_2 molecules, using the X-ray induced dissociation process as an internal clock that is read out via coincident detection of photoelectrons and fragment ions. By coincidence analysis of the kinetic energies of the ionic fragments and photoelectrons, the transition from a bound molecular dication to two isolated atomic ions is observed through the energy shift of the inner-shell electrons. Via ab-initio simulations, we are able to map characteristic features in the kinetic energy release and photoelectron spectrum to specific delay times between photoabsorptions. In contrast to previous studies where nuclear motions were typically revealed by measuring ion kinetics, our work shows that inner-shell photoelectron energies can also be sensitive probes of nuclear dynamics, which adds one more dimension to the study of light-matter interactions with X-ray pulses.

High-resolution macromolecular crystallography at the FemtoMAX beamline with time-over-threshold photon detection.

Protein dynamics contribute to protein function on different time scales. Ultrafast X-ray diffraction snapshots can visualize the location and amplitude of atom displacements after perturbation. Since amplitudes of ultrafast motions are small, high-quality X-ray diffraction data is necessary for detection. Diffraction from bovine trypsin crystals using single femtosecond X-ray pulses was recorded at FemtoMAX, which is a versatile beamline of the MAX IV synchrotron. The time-over-threshold detection made it possible that single photons are distinguishable even under short-pulse low-repetition-rate conditions. The diffraction data quality from FemtoMAX beamline enables atomic resolution investigation of protein structures. This evaluation is based on the shape of the Wilson plot, cumulative intensity distribution compared with theoretical distribution, I/σ, Rmerge/Rmeas and CC1/2 statistics versus resolution. The FemtoMAX beamline provides an interesting alternative to X-ray free-electron lasers when studying reversible processes in protein crystals.

Converting conventional electron accelerators to high peak brilliance Compton light sources

Several proposals have been put forward for converting electron accelerators to inverse Compton scattering (ICS) gamma sources. Typical approaches suggest combining near-IR solid-state lasers operating continuously at a multimegahertz repetition rate with e-beams when setting their interaction point inside a field-enhancement, Fabry-Perot optical cavity. We introduce here an alternative method of pairing particle accelerator beams with trains of long-wave-infrared, ${\ensuremath{\lambda}}_{L}\ensuremath{\approx}9--11\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ pulses from a picosecond ${\mathrm{CO}}_{2}$ laser of a novel architecture operating in a repetitive pulse-burst mode. Because of a considerable increase in the laser energy per pulse, combined with an order-of-magnitude higher number of laser photons per joule of laser energy, our approach allows us to increase the ICS peak flux and brilliance by 4 orders of magnitude compared to previous proposals while maintaining high (${10}^{11}--{10}^{12}\text{ }\text{ }\mathrm{ph}/\mathrm{s}$) average flux. This outcome is supported by the examples of the $\mathrm{DA}\mathrm{\ensuremath{\Phi}}\mathrm{NE}$ and CBETA accelerator facilities, where ${10}^{20}--{10}^{21}\text{ }\text{ }\mathrm{ph}/(\mathrm{s}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{mm}}^{2}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{mrad}}^{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.1%BW)$ peak brilliances at 50--1000 keV photon energy range can be achieved and is comparable or exceeds the capabilities of contemporary synchrotron light sources at hard x rays. Such high-brightness ICS sources will find applications in pump-probe and other ultrafast studies that require building up meaningful datasets on a single x-ray pulse.

Production of 100-TW single attosecond x-ray pulse

Attosecond light sources have provided insight into the fastest atomic-scale electronic dynamics. True attosecond-pump–attosecond-probe experiments require a single attosecond pulse at high intensity and large photon energy, a challenge that has yet to be conquered. Here we show 100-TW single attosecond x-ray pulses with unprecedented intensity of 10 21 W / c m 2 and duration 8.0 as can be produced by intense laser irradiation of a capacitor-nanofoil target composed of two separate nanofoils. In the interaction, a strong electrostatic potential develops between the two foils, which drags electrons out of the second foil and piles them up in vacuum, forming an ultradense relativistic electron nanobunch. This nanobunch reaches both high density and high energy in only half a laser cycle and smears out in others, resulting in coherent synchrotron emission of a single, intense attosecond pulse. Such a pulse enables the capture and control of electron motion at the picometer–attosecond scale.

Characterizing the intrinsic properties of individual XFEL pulses via single-particle diffraction.

With each single X-ray pulse having its own characteristics, understanding the individual property of each X-ray free-electron laser (XFEL) pulse is essential for its applications in probing and manipulating specimens as well as in diagnosing the lasing performance. Intensive research using XFEL radiation over the last several years has introduced techniques to characterize the femtosecond XFEL pulses, but a simple characterization scheme, while not requiring ad hoc assumptions, to address multiple aspects of XFEL radiation via a single data collection process is scant. Here, it is shown that single-particle diffraction patterns collected using single XFEL pulses can provide information about the incident photon flux and coherence property simultaneously, and the X-ray beam profile is inferred. The proposed scheme is highly adaptable to most experimental configurations, and will become an essential approach to understanding single X-ray pulses.

Picosecond pump-probe X-ray scattering at the Elettra SAXS beamline.

A new setup for picosecond pump-probe X-ray scattering at the Austrian SAXS beamline at Elettra-Sincrotrone Trieste is presented. A high-power/high-repetion-rate laser has been installed on-site, delivering UV/VIS/IR femtosecond-pulses in-sync with the storage ring. Data acquisition is achieved by gating a multi-panel detector, capable of discriminating the single X-ray pulse in the dark-gap of the Elettra hybrid filling mode. Specific aspects of laser- and detection-synchronization, on-line beam steering as well protocols for spatial and temporal overlap of laser and X-ray beam are also described. The capabilities of the setup are demonstrated by studying transient heat-transfer in an In/Al/GaAs superlattice structure and results are confirmed by theoretical calculations.

Hard X-ray von Hamos Spectrometer for Single-Pulse Emission Spectroscopy

We developed a hard X-ray spectrometer for the purpose of measuring X-ray emission spectrum excited by using single X-ray free electron laser (XFEL) pulses. A highly oriented pyrolytic graphite (HOPG) crystal was placed in the von Hamos geometry to focus X-rays of the equal energy on a specific point in detector plane. The spectrometer was tested at PAL-XFEL using Ni and NiO films. The Ni $${K_{{\beta _{13}}}}$$ X-ray emission line excited by using a single X-ray pulse was successfully resolved. If the much weaker Ni $${K_{{\beta _{25}}}}$$ line is to be observed, data must be accumulated with a few thousands of X-ray pulses. The spectrometer energy resolving power, E/ΔE, was estimated to be 7500. This spectrometer can be utilized to conduct various X-ray emission and absorption measurements using XFELs.

Compact hard X-ray split-and-delay line for studying ultrafast dynamics at free-electron laser sources.

A compact hard X-ray split-and-delay line for studying ultrafast dynamics at free-electron laser sources is presented. The device is capable of splitting a single X-ray pulse into two fractions to introduce time delays from -5 to 815 ps with femtosecond resolution. The split-and-delay line can operate in a wide and continuous energy range between 7 and 16 keV. Compact dimensions of 60 × 60 × 30 cm with a total weight of about 60 kg make it portable and suitable for direct installation in an experimental hutch. The concept of the device is based on crystal diffraction. The piezo-driven stages utilized in the device give nanometre positioning accuracy. On-line monitoring systems based on X-ray cameras and intensity monitors are implemented to provide active alignment feedback. Performance estimates of the system are also presented.

Single-shot time-resolved magnetic x-ray absorption at a free-electron laser

Ultrafast dynamics are generally investigated using stroboscopic pump-probe measurements, which characterize the sample properties for a single, specific time delay. These measurements are then repeated for a series of discrete time delays to reconstruct the overall time trace of the process. As a consequence, this approach is limited to the investigation of fully reversible phenomena. We recently introduced an off-axis zone plate based X-ray streaking technique, which overcomes this limitation by sampling the relaxation dynamics with a single femtosecond X-ray pulse streaked over a picosecond long time window. In this article we show that the X-ray absorption cross section can be employed as the contrast mechanism in this novel technique. We show that changes of the absorption cross section on the percent level can be resolved with this method. To this end we measure the ultrafast magnetization dynamics in CoDy alloy films. Investigating different chemical compositions and infrared pump fluences, we demonstrate the routine applicability of this technique. Probing in transmission the average magnetization dynamics of the entire film, our experimental findings indicate that the demagnetization time is independent of the specific infrared laser pump fluence. These results pave the way for the investigation of irreversible phenomena in a wide variety of scientific areas.

Generation of high-intensity single attosecond x-ray pulses with multi-laser beam superposition

The generation of high-intensity single attosecond x-ray pulses from high-order harmonic generation (HHG) has been investigated via superposition of multi-laser beams. The results can be separated into three parts: (i) single-color chirp modulation; (ii) ultraviolet (UV)-chirp two-color modulation; and (iii) multi-laser beam modulation. Firstly, for the single chirp modulation, with the introduction of the up-chirp, although the harmonic cutoff can be slightly extended, the efficiency of the HHG is reduced. With the introduction of the down-chirp, both the cutoff and the efficiency of the HHG can be improved compared with the up-chirp. Moreover, as the pulse duration increases, a larger harmonic cutoff can be found. Secondly, by appropriate addition of a UV pump pulse, the efficiency of HHG can be further enhanced due to UV-resonance-enhancement-ionization. Thirdly, with the assistance of the third controlling pulse or the inhomogeneous effect of the laser field, the harmonic cutoff can be further extended and keV-HHG can be produced. Finally, through Fourier transformation of some selected harmonics on the spectral continuum, high-intensity x-ray pulses (including the keV region) with durations of sub-90 as can be obtained.