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Creators/Authors contains: "Blackman, David R."

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  1. Abstract

    The concept of electron acceleration by a laser beam in vacuum is attractive due to its seeming simplicity, but its implementation has been elusive, as it requires efficient electron injection into the beam and a mechanism for counteracting transverse expulsion. Electron injection during laser reflection off a plasma mirror is a promising mechanism, but it is sensitive to the plasma density gradient that is hard to control. We get around this sensitivity by utilizing volumetric injection that takes place when a helical laser beam traverses a low-density target. The electron retention is achieved by choosing the helicity, such that the transverse field profiles are hollow while the longitudinal fields are peaked on central axis. We demonstrate using three-dimensional simulations that a 3 PW helical laser can generate a 50 pC low-divergence electron beam with a maximum energy of 1.5 GeV. The unique features of the beam are short acceleration distance (∼100 μm), compact transverse size, high areal density, and electron bunching (∼100 as bunch duration).

  2. Abstract

    The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates a0.03gcm3TMPTA foam target with a focused intensityIl=9.5×1017Wcm2. A third harmonic (λprobe266nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.