The optimum conditions of laser field depletion in laser-electron beam collision.

The laser field depletion in laser-electron beam collision is generally small. However, a properly chosen parameter of the laser and electron, the laser field depletion can be optimized. To access the laser energy evolution, simulations of laser-electron beam collision by Particle-in-Cell (PIC) simulation is performed. In this paper, the laser and electron parameters are chosen such that the ponderomotive force is compensated by the radiation reaction force in the head-on collision configuration. Then, the relativistic electron beam can quiver in the laser pulse for a longer time to increase the energies conversion. The optimum of laser field energy depletion is observed at $\gamma_0= a_0 \sim 400$ and limited beyond this point due to the impenetrability threshold. The total energy conversion from laser and electron beam into radiation emission is optimum at $\gamma_0= a_0 \sim 250$. This conversion efficiency can be up to several percent for an electron bunch with charges of a few nC. This efficient gamma-ray sources may provide some useful application in photonuclear experiments.