Laser-Accelerated Low-Divergence 15-MeV Quasimonoenergetic Electron Bunches at 1 kHz

We demonstrate laser wakefield acceleration of quasimonoenergetic electron bunches up to 15 MeV at 1-kHz repetition rate with 2.5-pC charge per bunch and a core with < 7−mrad beam divergence. Acceleration is driven by 5-fs, < 2.7−mJ laser incident on a thin, near-critical-density hydrogen gas jet. Low beam divergence is attributed to reduced sensitivity to laser carrier-envelope phase slip, achieved in two ways using gas jet positon control and laser polarization: (i) electron injection into the wake on the gas jet’s plasma density downramp and (ii) use of circularly polarized drive pulses. These results demonstrate the generation of high-quality electron beams from a few-cycle-pulse-driven laser plasma accelerator without the need for carrier-envelope phase stabilization.