Laser-accelerated electron beams at 1 GeV using optically-induced shock injection.

In recent years, significant progress has been made in laser wakefield acceleration (LWFA), both regarding the increase in electron energy, charge and stability as well as the reduction of bandwidth of electron bunches. Simultaneous optimization of these parameters is, however, still the subject of an ongoing effort in the community to reach sufficient beam quality for next generation's compact accelerators. In this report, we show the design of slit-shaped gas nozzles providing centimeter-long supersonic gas jets that can be used as targets for the acceleration of electrons to the GeV regime. In LWFA experiments at the Centre for Advanced Laser Applications, we show that electron bunches are accelerated to [Formula: see text] using these nozzles. The electron bunches were injected into the laser wakefield via a laser-machined density down-ramp using hydrodynamic optical-field-ionization and subsequent plasma expansion on a ns-timescale. This injection method provides highly controllable quasi-monoenergetic electron beams with high charge around [Formula: see text], low divergence of [Formula: see text], and a relatively small energy spread of around [Formula: see text] at [Formula: see text]. In contrast to capillaries and gas cells, the scheme allows full plasma access for injection, probing or guiding in order to further improve the energy and quality of LWFA beams.

Measuring spatio-temporal couplings using modal spatio-spectral wavefront retrieval.

Knowledge of spatio-temporal couplings such as pulse-front tilt or curvature is important to determine the focused intensity of high-power lasers. Common techniques to diagnose these couplings are either qualitative or require hundreds of measurements. Here we present both a new algorithm for retrieving spatio-temporal couplings, as well as novel experimental implementations. Our method is based on the expression of the spatio-spectral phase in terms of a Zernike-Taylor basis, allowing us to directly quantify the coefficients for common spatio-temporal couplings. We take advantage of this method to perform quantitative measurements using a simple experimental setup, consisting of different bandpass filters in front of a Shack-Hartmann wavefront sensor. This fast acquisition of laser couplings using narrowband filters, abbreviated FALCON, is easy and cheap to implement in existing facilities. To this end, we present a measurement of spatio-temporal couplings at the ATLAS-3000 petawatt laser using our technique.

Prevalence of malnutrition and its associated outcomes in pediatric patients with scoliosis undergoing elective posterior spinal fusion or spine growth modulation - a retrospective review.

Recent attention within pediatric orthopedics focuses on the prevalence and prevention of post-operative complications, including surgical site infections (SSIs). While poor nutrition status has been noted as a risk factor, various definitions have been utilized. The aim of this retrospective chart review was to utilize the Academy of Nutrition and Dietetics (AND) and the American Society for Parenteral and Enteral Nutrition (ASPEN) diagnostic criteria to determine both the prevalence of malnutrition in pediatric patients undergoing spine deformity surgery and its influence on the prevalence of post-operative complications. A total of 2603 patients had a spine procedure between 2012 and 2018. Patients were excluded if they were less than 2 years of age or greater than 18 years of age and/or did not have their spine procedure completed at Children's Wisconsin. Patients who met inclusion criteria and had an irrigation and debridement (I&D) were selected for an I&D group. From the remaining charts, 127 patients were randomly selected for the non-I&D group. Patients in both groups were further divided into well-nourished and malnourished groups. T-tests and chi square tests were used to determine statistical significance. We found that 50% of patients who had an I&D had malnutrition during their clinical course. This is compared with 17% of patients who didn't require an I&D. Additionally, patients requiring multiple surgical interventions, had an increased prevalence of malnutrition. With the recent focus on reducing the prevalence of post-operative complications, the identification and treatment of malnutrition may be helpful in reducing post-operative complications.

Demonstration of a compact plasma accelerator powered by laser-accelerated electron beams.

Plasma wakefield accelerators are capable of sustaining gigavolt-per-centimeter accelerating fields, surpassing the electric breakdown threshold in state-of-the-art accelerator modules by 3-4 orders of magnitude. Beam-driven wakefields offer particularly attractive conditions for the generation and acceleration of high-quality beams. However, this scheme relies on kilometer-scale accelerators. Here, we report on the demonstration of a millimeter-scale plasma accelerator powered by laser-accelerated electron beams. We showcase the acceleration of electron beams to 128 MeV, consistent with simulations exhibiting accelerating gradients exceeding 100 GV m-1. This miniaturized accelerator is further explored by employing a controlled pair of drive and witness electron bunches, where a fraction of the driver energy is transferred to the accelerated witness through the plasma. Such a hybrid approach allows fundamental studies of beam-driven plasma accelerator concepts at widely accessible high-power laser facilities. It is anticipated to provide compact sources of energetic high-brightness electron beams for quality-demanding applications such as free-electron lasers.

Nonlinear plasma wavelength scalings in a laser wakefield accelerator.

Laser wakefield acceleration relies on the excitation of a plasma wave due to the ponderomotive force of an intense laser pulse. However, plasma wave trains in the wake of the laser have scarcely been studied directly in experiments. Here we use few-cycle shadowgraphy in conjunction with interferometry to quantify plasma waves excited by the laser within the density range of GeV-scale accelerators, i.e., a few 10^{18}cm^{-3}. While analytical models suggest a clear dependency between the nonlinear plasma wavelength and the peak potential a_{0}, our study shows that the analytical models are only accurate for driver strength a_{0}≲1. Experimental data and systematic particle-in-cell simulations reveal that nonlinear lengthening of the plasma wave train depends not solely on the laser peak intensity but also on the waist of the focal spot.

Hybrid LWFA-PWFA staging as a beam energy and brightness transformer: conceptual design and simulations.

We present a conceptual design for a hybrid laser-driven plasma wakefield accelerator (LWFA) to beam-driven plasma wakefield accelerator (PWFA). In this set-up, the output beams from an LWFA stage are used as input beams of a new PWFA stage. In the PWFA stage, a new witness beam of largely increased quality can be produced and accelerated to higher energies. The feasibility and the potential of this concept is shown through exemplary particle-in-cell simulations. In addition, preliminary simulation results for a proof-of-concept experiment in Helmholtz-Zentrum Dresden-Rossendorf (Germany) are shown. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Energy-Chirp Compensation in a Laser Wakefield Accelerator.

The energy spread in laser wakefield accelerators is primarily limited by the energy chirp introduced during the injection and acceleration processes. Here, we propose the use of longitudinal density tailoring to reduce the beam chirp at the end of the accelerator. Experimental data sustained by quasi-3D particle-in-cell simulations show that broadband electron beams can be converted to quasimonoenergetic beams of ≤10% energy spread while maintaining a high charge of more than 120 pC. In the linear and quasilinear regimes of wakefield acceleration, the method could provide even lower, subpercent level, energy spread.

Observation of Laser Power Amplification in a Self-Injecting Laser Wakefield Accelerator.

We report on the depletion and power amplification of the driving laser pulse in a strongly driven laser wakefield accelerator. Simultaneous measurement of the transmitted pulse energy and temporal shape indicate an increase in peak power from 187±11 TW to a maximum of 318±12 TW after 13 mm of propagation in a plasma density of 0.9×10^{18} cm^{-3}. The power amplification is correlated with the injection and acceleration of electrons in the nonlinear wakefield. This process is modeled by including a localized redshift and subsequent group delay dispersion at the laser pulse front.

High-Brilliance Betatron γ-Ray Source Powered by Laser-Accelerated Electrons.

Recent progress in laser-driven plasma acceleration now enables the acceleration of electrons to several gigaelectronvolts. Taking advantage of these novel accelerators, ultrashort, compact, and spatially coherent x-ray sources called betatron radiation have been developed and applied to high-resolution imaging. However, the scope of the betatron sources is limited by a low energy efficiency and a photon energy in the 10 s of kiloelectronvolt range, which for example prohibits the use of these sources for probing dense matter. Here, based on three-dimensional particle-in-cell simulations, we propose an original hybrid scheme that combines a low-density laser-driven plasma accelerator with a high-density beam-driven plasma radiator, thereby considerably increasing the photon energy and the radiated energy of the betatron source. The energy efficiency is also greatly improved, with about 1% of the laser energy transferred to the radiation, and the γ-ray photon energy exceeds the megaelectronvolt range when using a 15 J laser pulse. This high-brilliance hybrid betatron source opens the way to a wide range of applications requiring MeV photons, such as the production of medical isotopes with photonuclear reactions, radiography of dense objects in the defense or industrial domains, and imaging in nuclear physics.

3D printing of gas jet nozzles for laser-plasma accelerators.

Recent results on laser wakefield acceleration in tailored plasma channels have underlined the importance of controlling the density profile of the gas target. In particular, it was reported that the appropriate density tailoring can result in improved injection, acceleration, and collimation of laser-accelerated electron beams. To achieve such profiles, innovative target designs are required. For this purpose, we have reviewed the usage of additive layer manufacturing, commonly known as 3D printing, in order to produce gas jet nozzles. Notably we have compared the performance of two industry standard techniques, namely, selective laser sintering (SLS) and stereolithography (SLA). Furthermore we have used the common fused deposition modeling to reproduce basic gas jet designs and used SLA and SLS for more sophisticated nozzle designs. The nozzles are characterized interferometrically and used for electron acceleration experiments with the Salle Jaune terawatt laser at Laboratoire d'Optique Appliquée.

Electron Rephasing in a Laser-Wakefield Accelerator.

An important limit for energy gain in laser-plasma wakefield accelerators is the dephasing length, after which the electron beam reaches the decelerating region of the wakefield and starts to decelerate. Here, we propose to manipulate the phase of the electron beam in the wakefield, in order to bring the beam back into the accelerating region, hence increasing the final beam energy. This rephasing is operated by placing an upward density step in the beam path. In a first experiment, we demonstrate the principle of this technique using a large energy spread electron beam. Then, we show that it can be used to increase the energy of monoenergetic electron beams by more than 50%.

Demonstration of relativistic electron beam focusing by a laser-plasma lens.

Laser-plasma technology promises a drastic reduction of the size of high-energy electron accelerators. It could make free-electron lasers available to a broad scientific community and push further the limits of electron accelerators for high-energy physics. Furthermore, the unique femtosecond nature of the source makes it a promising tool for the study of ultrafast phenomena. However, applications are hindered by the lack of suitable lens to transport this kind of high-current electron beams mainly due to their divergence. Here we show that this issue can be solved by using a laser-plasma lens in which the field gradients are five order of magnitude larger than in conventional optics. We demonstrate a reduction of the divergence by nearly a factor of three, which should allow for an efficient coupling of the beam with a conventional beam transport line.

Compact laser accelerators for X-ray phase-contrast imaging.

Advances in X-ray imaging techniques have been driven by advances in novel X-ray sources. The latest fourth-generation X-ray sources can boast large photon fluxes at unprecedented brightness. However, the large size of these facilities means that these sources are not available for everyday applications. With advances in laser plasma acceleration, electron beams can now be generated at energies comparable to those used in light sources, but in university-sized laboratories. By making use of the strong transverse focusing of plasma accelerators, bright sources of betatron radiation have been produced. Here, we demonstrate phase-contrast imaging of a biological sample for the first time by radiation generated by GeV electron beams produced by a laser accelerator. The work was performed using a greater than 300 TW laser, which allowed the energy of the synchrotron source to be extended to the 10-100 keV range.

Bacteroides fragilis endocarditis.

We recently diagnosed and treated an unusual case of primary endocarditis due to Bacteroides fragilis, for which no underlying etiology was found. Antibiotic treatment involved multiple parenteral and oral antibiotics, and sensitivity studies allowed choice of antibiotics. Despite complications, the patient was cured. Few cases of Bacteroides fragilis endocarditis have been reported, and therapy has changed with newer antibiotics.

Thymosin-dependent T-lymphocyte response in inflammatory bowel disease.

Peripheral blood "total" and "avid" thymus-dependent (T) lymphocytes were enumerated in 45 patients with Crohn's disease (CD) and in 23 patients with ulcerative patients (UC) by using the spontaneous rosette technique (ER). The in vitro effect of thymosin fraction 5, a polypeptide extract of the thymus gland, on avid ER formatin was also determined in these patients. The proportion and number of "total" ER were lower in patients with CD (P < 0.02), but not with UC, when compared with controls. More impressive differences were observed when "avid" ER were determined in patients with CD (P < 0.001) and UC (P < 0.05). Incubation with thymosin resulted in a significant increase in "avid" ER in patients with CD and UC, with no such effect observed in the controls. These results indicate that the determination of "avid" rather than "total" ER provides a more sensitive method for detecting alterations in T-cell immune competence. In addition, it is suggested that there is an increased number of circulating T-lymphocytes in CD and UC capable of responding to exogenous thymic factors. This may indicate the presence of a thymosin-responsive immunodeficiency state in these diseases.

Influence of SRBC/lymphocyte ratio on T-cell rosettes in alcoholic liver disease and inflammatory bowel disease.

Thymus-derived (T) rosette-forming cells were enumerated in patients with alcoholic liver disease and in patients with inflammatory bowel disease using variable sheep red blood cell (SRBC)/lymphocyte ratios. SRBC/lymphocyte ratios of 60:1 and 32:1 did not reveal significant differences from controls in Crohn's disease. The percentage, but not absolute count, of T cells was significantly reduced in alcoholic hepatitis at the 60:1 ratio. Both the percentage and absolute count of T cells were reduced in alcoholic hepatitis and Crohn's disease with the 8:1 ratio. No significant reduction in T cells was seen at any ratio in patients with compensated alcoholic cirrhosis or ulcerative colitis. Use of a SRBC/lymphocyte ratio of 8:1 indentifies T cells which demonstrate an avidity for SRBC. This avidity may be related to the density of SRBC receptors on the surface of T cells and/or the affinity of these receptor sites for SRBC. Use of the 8:1 ratio may provide a more sensitive means by which to monitor changes in T-cell rosettes in patients suspected of having an altered cellular immune state.

Neisseria meningitidis: a cause of nosocomial pneumonia.

A 24-year-old man developed coma and many neurologic abnormalities for 2 weeks after ingesting phencyclidine. On admission, pulmonary aspiration occurred, for which he was given large doses of methylprednisolone, clindamycin, and gentamicin. These antimicrobial drugs were continued for 2 weeks until new pulmonary infiltrates were recognized. Neisseria meningitidis was subsequently isolated from cultures of conjunctival discharge, sputum, and blood and found to be resistant to clindamycin and gentamicin. N. meningitidis as a cause of nosocomial pneumonia in the setting of broad spectrum antimicrobial drugs is discussed.