Plasma electron acceleration driven by a long-wave-infrared laser
Rafal Zgadzaj, James Welch, Y. Cao, L. D. Amorim, Aiqi Cheng, Akshay Gaikwad, P. Iapozzutto, Prabhat Kumar, Vladimir Litvinenko, Irina Petrushina, Roman Samulyak, Navid Vafaei-Najafabadi, C. Joshi, Chaojie Zhang, M. Babzien, Mikhail Fedurin, Rotem Kupfer, K. Kusche, M. Palmer, Igor Pogorelsky, Mikhail Polyanskiy, C. Swinson, M. C. Downer
Abstract
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 λ L ~ 1 μ m. Longer- λ L 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 2 laser ( λ L ≈ 10 μ m). Through optical scattering experiments, we observed wakes that 4-ps CO 2 pulses with < 1/2 terawatt (TW) peak power drove in hydrogen plasma of electron density down to 4 × 10 17 cm −3 (1/100 atmospheric density) via a self-modulation (SM) instability. Shorter, more powerful CO 2 pulses drove wakes in plasma down to 3 × 10 16 cm −3 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.