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We report experimental results on laser-driven electron acceleration with low divergence. The electron beam was generated by focussing 750mJ, 42 fs laser pulses into a gas-filled capillary discharge waveguide at electron densities in the range between 10¹8 and 10¹9 cm^-3. Quasi-monoenergetic electron bunches with energies as high as 500 MeV have been detected, with features reaching up to 1 GeV, albeit with large shot-to-shot fluctuations. A more stable regime with higher bunch charge (20-45 pC) and less energy (200-300 MeV) could also be observed. The beam divergence and the pointing stability are around or below 1 mrad and 8 mrad, respectively. These findings are consistent with self-injection of electrons into a breaking plasma wave.
Karsch et al. (2007) studied this question.