Electron, Positron, and Photon Wakefield Acceleration: Trapping, Wake Overtaking, and Ponderomotive Acceleration

The electron, positron, and photon acceleration in the first cycle of a laser-driven wakefield is investigated. Separatrices between different types of the particle motion (trapped, reflected by the wakefield and ponderomotive potential, and transient) are demonstrated. The ponderomotive acceleration of electrons can be largely compensated by the wakefield action, in contrast to positrons and positively charged mesons. The electron bunch energy spectrum is analyzed. The maximum upshift of an electromagnetic wave frequency during reflection from the wakefield is obtained.

Figure 1

(a) The wakefield excited by the laser pulse; (b) normalized electron and scaled ion density. Phase portrait for the (c) electron, (e) positron, and (f) photon. (d) The electron ponderomotive basin close-up. The thick solid line is for separatrices, the thin solid line for other orbits; the thick dotted line in (c) and (e) is for $p_x={\beta }_{\mathrm{ph}}{\gamma }_{\mathrm{ph}}[1+a^2(X){]}^{1/2}$ and in (f) is for $k_{\parallel }c={\beta }_{\mathrm{ph}}{\gamma }_{\mathrm{ph}}{\omega }_{pe}(X)$.

Figure 2

The energy spectrum of the electron bunch: contributions from (a) particles scattered about the top of the separatrix and (b) particles that overtake the laser pulse.