We present experimental studies on ion acceleration from ultra-thin diamond-like carbon (DLC) foils irradiated by ultra-high contrast laser pulses of energy 0.7 J focussed to peak intensities of 5 × 10 19 W/cm 2 . A reduction in electron heating is observed when the laser polarization is changed from linear to circular, leading to a pronounced peak in the fully ionized carbon spectrum at the optimum foil thickness of 5.3 nm. Two-dimensional particle-in-cell (PIC) simulations reveal, that those C 6+ ions are for the first time dominantly accelerated in a phase-stable way by the laser radiation pressure.
Laser plasma accelerators 1 have produced high-quality electron beams with GeV energies from cm-scale devices 2 and are being investigated as hyperspectral fs light sources producing THz to γ-ray radiation 3-5 , and as drivers for future highenergy colliders 6,7 . These applications require a high degree of stability, beam quality and tunability. Here we report on a technique to inject electrons into the accelerating field of a laser-driven plasma wave and coupling of this injector to a lower-density, separately tunable plasma for further acceleration. The technique relies on a single laser pulse powering a plasma structure with a tailored longitudinal density profile, to produce beams that can be tuned in the range of 100-400 MeV with per-cent-level stability, using laser pulses of less than 40 TW. The resulting device is a simple stand-alone accelerator or the front end for a multistage higher-energy accelerator.Producing high-quality electron beams from an accelerator requires electron injection into the accelerating field to be localized in time and space. For laser plasma accelerators (LPAs) that rely on homogeneous plasmas driven with single laser pulses, continuous injection can occur when driving large-amplitude plasma waves (wakefields), resulting in large energy spread. Lower energy spread can be achieved through termination of injection by operating near the injection threshold or by injecting enough charge to suppress the wake amplitude (that is, beam loading). Subsequent termination of the accelerating process at dephasing (that is, when electrons are starting to outrun the accelerating wave) minimizes energy spread. These mechanisms have produced per-cent-level energy-spread beams 2,8-10 , but small changes in parameters can result in large changes in beam quality. As a result, tunability has been limited, necessitating the development of a simple, robust and controlled injection technique combined with an independently controllable accelerating stage.In general, injection of electrons into a plasma wave occurs when the velocity of background electrons approaches the wake phase velocity. Laser-based methods for boosting the electron velocity have been proposed 11,12 and implemented 13,14 to achieve tunable electron beams, but require sophisticated alignment and synchronization of the multiple laser pulses. Injection can also be triggered by introducing electrons into the correct phase of the wake through ionization 15 , but so far the technique has resulted in broad energy-spread beams with high divergence 16,17 . A different approach, that relies on a single laser pulse for powering the LPA, is to momentarily slow down the wake phase velocity to facilitate trapping 18 . The control of the wake phase velocity can be achieved by tailoring the nonlinear plasma wavelength λ p (z) along the longitudinal coordinate z, through control of the electron density n e and the laser parameters. Specifically, λ p (z) = λ p0 (z)F , where the linear plasma wavelength λ p0 (µm) ≈ 3.3 × 10 10 / √ n e (cm −3 ) and F ...
X-ray spectroscopy is used to obtain single-shot information on electron beam emittance in a low-energy-spread 0.5 GeV-class laser-plasma accelerator. Measurements of betatron radiation from 2 to 20 keV used a CCD and single-photon counting techniques. By matching x-ray spectra to betatron radiation models, the electron bunch radius inside the plasma is estimated to be ~0.1 μm. Combining this with simultaneous electron spectra, normalized transverse emittance is estimated to be as low as 0.1 mm mrad, consistent with three-dimensional particle-in-cell simulations. Correlations of the bunch radius with electron beam parameters are presented.
We analyze pulse self-compression in femtosecond filaments, both experimentally and numerically. We experimentally demonstrate the compression of 45 fs pulses down to a duration of 7.4 fs at millijoule pulse energies. This sixfold compression in a self-generated filament does not require any means for dispersion compensation and is highly efficient. We compare our results to numerical simulations, providing a complete propagation model that accounts for full dispersion, pressure variations, Kerr nonlinearity and plasma generation in multiphoton and tunnel regimes. The equations are numerically integrated and allow for a quantitative comparison with the experiment. Our experiments and numerical simulations reveal a characteristic spectrotemporal structure of the self-compressed pulses, consisting of a compressible blue wing and an incompressible red pedestal. We explain the underlying mechanism that leads to this structure and examine the scalability of filament self-compression with respect to pulse energy and gas pressure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.