Double-Relativistic-Electron-Layer Proton Acceleration with High-Contrast Circular-Polarization Laser Pulses

A new laser-proton acceleration scheme consisting of two relativistic electron layers, a suprathermal electron layer and a thermal electron cloud is proposed for a0 80σ0, where a0 is the normalized laser field and σ0 is the normalized plasma surface density. This is essentially different from target normal sheath acceleration and radiation pressure acceleration. The persistent opaqueness of the first relativistic electron layer for the incident circular-polarization laser pulse and electron recirculation are key points in forming the new acceleration scheme. A proton beam with a uniform energy distribution in the energy range 1–2 GeV and a monoenergetic proton beam with hundreds of MeV have been predicted for a0 = 39.5.