Energy partition, γ-ray emission, and radiation reaction in the near-quantum electrodynamical regime of laser-plasma interaction

摘要

When extremely intense lasers (I≥10~(22)W/cm~2) interact with plasmas, a significant fraction of the pulse energy is converted into photon emission in the multi-MeV energy range. This emission results in a radiation reaction (RR) force on electrons, which becomes important at ultrahigh intensities. Using three-dimensional particle-in-cell simulations which include a quantum electrodynamics model for the γ–photons emission, the corresponding RR force and electron-positron pair creation, the energy partition in the laser-plasma system is investigated. At sufficiently high laser amplitudes, the fraction of laser energy coupled to electrons decreases, while the energy converted to γ-photons increases. The interaction becomes an efficient source of γ-rays when I>10~(24) W/cm~2, with up to 40% of the laser energy converted to high-energy photons. A systematic study of energy partition and c-photon emission angle shows the influence of laser intensity and polarization for two plasma conditions: high-density carbon targets and a low-density hydrogen targets. We find that in the opaque region, the laser-to-photon conversion efficiency scales as I_0~(3/2) for linearly polarized and I_0~(2-2.5) for circularly polarized lasers, respectively. In the relativistically transparent regime, the power-laws merge into I_0~(1/2) for both polarizations and photon emission peaks in the forward direction with a relatively small divergence angle (<20°), resulting in a collimated γ-ray beam.