Strongly-Mismatched Regime of Nonlinear Laser-Plasma Acceleration: Optimization of Laser to Energetic Particle Efficiency

A strongly mismatched regime of self-guided nonlinear laser-plasma acceleration in the bubble regime is modeled for optimization of Laser to Particle energy efficiency with application to recently proposed laser positron accelerator. The strong mismatch, in contrast with the matched condition, arises from the incident laser spot-size being much larger than that needed for equilibration of the laser ponderomotive and electron-ion charge-separation force in the plasma bubble. This is shown to be favorable for optimization of large self-injected electron charge and ultra-low transverse emittance. The prominent signatures of the mismatched regime, strong optical-shock excitation and bubble elongation, are validated using multi-dimensional Particle-In-Cell simulations. This work thus uncovers a generalized regime that is shown to have been favored by many laser-plasma acceleration experiments and opens a novel pathway for a wide-range of future applications.