Plasma electron acceleration driven by a long-wave-infrared laser

Abstract

Laser-driven plasma accelerators provide tabletop sources of relativistic electron bunches and femtosecond x-ray pulses, but usually require petawatt-class solid-state-laser pulses of wavelength λsub> ≈ 1 μm. Longer-λsub> lasers can potentially accelerate higher-quality bunches, since they require less power to drive larger wakes in less dense plasma. Here, we report on a self-injecting plasma accelerator driven by a long-wave-infrared laser: a chirped-pulse-amplified CO<2sub> laser (λ 10 μm). Through optical scattering experiments, we observed wakes that 4-ps CO<2sub> pulses with < 1/2 terawatt (TW) peak power drove in hydrogen plasma of density down to 1/100 atmosphere via a self-modulation (SM) instability. Shorter, more powerful CO<2sub> pulses drove wakes in plasma down to 1/1000 atmosphere that captured and accelerated plasma electrons to relativistic energy. Collimated quasi-monoenergetic features in the electron output marked the onset of a transition from SM to ″bubble-regime″ acceleration, portending future higher-quality accelerators driven by yet shorter, more powerful pulses.