Demonstration of quasi-monoenergetic electron-beam generation in laser-driven plasma acceleration

The generation of a quasi-monoenergetic electron beam in laser-driven plasma acceleration is reported. A monoenergetic electron beam with an energy of 7 MeV was emitted from a high-density plasma (electron density >1020 cm-3) produced by a 2 TW 50 fs laser pulse. The divergence of the monoenergetic beam was ±1.2 deg. The first Stokes satellite peak of stimulated forward Raman scattering was observed in the spectrum of the light transmitted through the plasma. The plasma wave was excited in the region of which electron density was around 1.3x1020 cm-3. The acceleration length was estimated to be 500 μm from the length of the side-scattered light image. It is considered that the monoenergetic beam generation is due to the matching of the acceleration length to the dephasing length determined by the velocity difference between the accelerated electrons and the plasma wave