Monoenergetic High-Energy Ion Source via Femtosecond Laser Interacting With a Microtape *

Laser-based ion sources are characterized by unsurpassed acceleration gradient and exceptional beam emittance. They are promising candidates for next-generation accelerator towards diverse applications. However, ion beams achieved currently have limitations in energy spread and peak energy. In this talk, we report a novel method to achieve monoenergetic proton beams with energy spread at 1% level and peak energy of hundred MeV by using a readily available femtosecond laser interacting with a microtape. As the laser sweeps along the tape, it drags out a huge charge (∼100 nC) of collimated electrons and accelerates them to superponderomotive energies. When this dense electron current reaches the rear edge of the tape, it induces a strong electrostatic field. Due to the excessive space charge of electrons, the longitudinal field becomes bunching while the transverse is focusing for protons. Together, this leads to a highly monoenergetic energy spectrum and much higher proton energy as compared to results from typical target normal sheath acceleration and radiation pressure acceleration at the same parameters.