We demonstrate for the first time a proof-of-principle experiment for nanoparticle-assisted laser wakefield acceleration. Nanoparticles generated through laser ablation of an aluminium target were introduced into a helium plasma and used to trigger the injection of electrons into the nonlinear plasma wake excited by an 800 nm wavelength, 1.8 J energy, femtosecond duration pulse laser. High-energy electron beams were produced, observing a significant enhancement of the electron beam energy, energy spread and divergence compared with the case when electrons are self-injected. For instance, the best quality electron bunches presented peak energy up to 338 MeV with a relative energy spread of 4.7% and a vertical divergence of 5.9 mrad. The initial results are very promising and motivate further theoretical and experimental research into developing the nanoparticle-assisted laser wakefield acceleration.

High-power terahertz radiation was observed to be emitted from a gas jet irradiated by 100-terawatt-class laser pulses in the laser-wakefield acceleration of electrons. The emitted terahertz radiation was characterized in terms of its spectrum, polarization, and energy dependence on the accompanying electron bunch energy and charge under various gas target conditions. With a nitrogen target, more than 4 mJ of energy was produced at <10 THz with a laser-to-terahertz conversion efficiency of ~0.15%. Such strong terahertz radiation is hypothesized to be produced from plasma electrons accelerated by the ponderomotive force of the laser and the plasma wakefields on the time scale of the laser pulse duration and plasma period. This model is examined with analytic calculations and particle-in-cell simulations to better understand the generation mechanism of high-energy terahertz radiation in laser-wakefield acceleration.

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