We experimentally demonstrate generation of quasi-mono-energetic electrons from pure nitrogen gas via ionization injection induced by self-evolved laser pulses. By means of self-focusing and self-compression, we are able to reduce the injection length to 200 and obtain the acceleration distance over several Rayleigh lengths that leads to the generation of quasi-mono-energetic electron beams with peak energy of 185 MeV and energy spread of 6%. This uncomplicated and maneuverable method suggests that the interaction of femtosecond laser pulses with moderate energy ∼1 J with pure nitrogen gas is advantageous for achieving stable and small energy spread electron beam.
Controlled electron injection in a laser-plasma accelerator