Evidence-Based Practice among Dutch Occupational Therapists: Barriers, Perceptions, and Use of Resources

This study explored how evidence-based practice (EBP) is perceived by Dutch occupational therapists (OTs), what sources of evidence they use to make clinical decisions, and what barriers they experience when implementing EBP. Two-hundred members of the Dutch Association of Occupational Therapy (EN) practicing as OTs in the Netherlands were randomly selected. The data collection process resulted in a 54.6% response rate. Dutch OTs valued EBP greatly. Participants reported evaluating the quality of research evidence to be the greatest barrier to EBP. A barrier unique to this study was difficulty in using evidence written in foreign languages, which was likely to decrease the use of more robust sources of evidence. Support from the workplace was important in increasing the use of EBP. The findings suggested that EBP is not implemented optimally in the Dutch OT community. Cooperation between OTs, employers, educators, researchers, and EN is necessary in addressing existing barriers

Tunable X-ray source by Thomson scattering during laser-wakefield acceleration

We report results on all-optical Thomson scattering intercepting the acceleration process in a laser wakefield accelerator. We show that the pulse collision position can be detected using transverse shadowgraphy which also facilitates alignment. As the electron beam energy is evolving inside the accelerator, the emitted spectrum changes with the scattering position. Such a configuration could be employed as accelerator diagnostic as well as reliable setup to generate x-rays with tunable energy

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 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 (FDM) 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 Appliqu\'ee

Energy boost in laser wakefield accelerators using sharp density transitions

The energy gain in laser wakefield accelerators is limited by dephasing between the driving laser pulse and the highly relativistic electrons in its wake. Since this phase depends on both the driver and the cavity length, the effects of dephasing can be mitigated with appropriate tailoring of the plasma density along propagation. Preceding studies have discussed the prospects of continuous phase-locking in the linear wakefield regime. However, most experiments are performed in the highly non-linear regime and rely on self-guiding of the laser pulse. Due to the complexity of the driver evolution in this regime it is much more difficult to achieve phase locking. As an alternative we study the scenario of rapid rephasing in sharp density transitions, as was recently demonstrated experimentally. Starting from a phenomenological model we deduce expressions for the electron energy gain in such density profiles. The results are in accordance with particle-in-cell simulations and we present gain estimations for single and multiple stages of rephasing

Multi-objective and multi-fidelity Bayesian optimization of laser-plasma acceleration

Beam parameter optimization in accelerators involves multiple, sometimes competing objectives. Condensing these multiple objectives into a single objective unavoidably results in bias towards particular outcomes that do not necessarily represent the best possible outcome for the operator in terms of parameter optimization. A more versatile approach is multi-objective optimization, which establishes the trade-off curve or Pareto front between objectives. Here we present first results on multi-objective Bayesian optimization of a simulated laser-plasma accelerator. We find that multi-objective optimization is equal or even superior in performance to its single-objective counterparts, and that it is more resilient to different statistical descriptions of objectives. As a second major result of our paper, we significantly reduce the computational costs of the optimization by choosing the resolution and box size of the simulations dynamically. This is relevant since even with the use of Bayesian statistics, performing such optimizations on a multi-dimensional search space may require hundreds or thousands of simulations. Our algorithm translates information gained from fast, low-resolution runs with lower fidelity to high-resolution data, thus requiring fewer actual simulations at highest computational cost. The techniques demonstrated in this paper can be translated to many different use cases, both computational and experimental

All-optical Compton scattering at shallow interaction angles

All-optical Compton sources combine laser wakefield accelerators and intense scattering pulses to generate ultrashort bursts of backscattered radiation. The scattering pulse plays the role of a short-period undulator in which relativistic electrons oscillate and emit x-ray radiation. To date, most of the working laser-plasma accelerators operate preferably at energies of a few hundreds of MeV and the Compton sources developed so far produce radiation in the range from hundreds of keV to a few MeV. However, for such applications as medical imaging and tomography the relevant energy range is 10-100 keV. In this article, we discuss different scattering geometries for the generation of X-rays in this range. Through numerical simulations, we study the influence of electron beam parameters on the backscattered photons. We find that the spectral bandwidth remains constant for beams of the same emittance regardless of the scattering geometry. A shallow interaction angle of 30 degrees or less seems particularly promising for imaging applications given parameters of existing laser-plasma accelerators. Finally, we discuss the influence of the radiation properties for potential applications in medical imaging and non-destructive testing

Quick X-ray microtomography using a laser-driven betatron source

Laser-driven X-ray sources are an emerging alternative to conventional X-ray tubes and synchrotron sources. We present results on microtomographic X-ray imaging of a cancellous human bone sample using synchrotron-like betatron radiation. The source is driven by a 100-TW-class titanium-sapphire laser system and delivers over $10^8$ X-ray photons per second. Compared to earlier studies, the acquisition time for an entire tomographic dataset has been reduced by more than an order of magnitude. Additionally, the reconstruction quality benefits from the use of statistical iterative reconstruction techniques. Depending on the desired resolution, tomographies are thereby acquired within minutes, which is an important milestone towards real-life applications of laser-plasma X-ray sources