Generation of quasi-monoenergetic electron beams with small normalized divergences angle from a 2 TW laser facility.

We report the generation of a 6 pC, 23 MeV electron bunch with the energy spread ± 3.5% by using 2 TW, 80 fs high contrast laser pulses interacting with helium gas targets. Within the optimized experimental condition, we obtained quasi-monoenergetic electron beam with an ultra-small normalized divergence angle of 92 mrad, which is at least 5 times smaller than the previous LPA-produced bunches. We suggest the significant decrease of the normalized divergence angles is due to smooth transfer from SM-LWFA to LWFA. Since the beam size in LPA is typically small, this observation may explore a simple way to generate ultralow normalized emittance electron bunches by using small-power but high-repetition-rate laser facilities.