Laser wakefield acceleration with mid-IR laser pulses

We report on, to the best of our knowledge, the first results of laser plasma wakefield acceleration driven by ultrashort mid-infrared (IR) laser pulses (lambda = 3.9 mu m, 100 fs, 0.25 TW), which enable near-and above-critical density interactions with moderate-density gas jets. Relativistic electron acceleration up to similar to 12 MeV occurs when the jet width exceeds the threshold scale length for relativistic self-focusing. We present scaling trends in the accelerated beam profiles, charge, and spectra, which are supported by particle-in-cell simulations and time-resolved images of the interaction. For similarly scaled conditions, we observe significant increases in the accelerated charge, compared to previous experiments with near-infrared (lambda = 800 nm) pulses. (c) 2018 Optical Society of America