Figure 2.

Monoenergetic, relativistic electrons from laser-driven linear-field acceleration in free space. (a–d) depict the behavior of the optical and electron pulses at various times during the laser-electron interaction. These instants are marked with circles in (e), which show the evolution of the electron pulse’s mean kinetic energy as a function of distance (laser focus at z = 0). The final (f) normalized trace-space emittance and (g) energy distribution describe a relativistic, high-quality and quasi-monoenergetic electron pulse. The laser and electron pulse parameters from Fig. 1 were used here. Although the electron pulse eventually acquires a relatively large transverse size (see (f)), its low trace-space emittance implies that it is readily re-compressed with appropriate focusing elements (e.g., magnetic solenoid).