Influence of Ion Mass on Laser-Energy Absorption and Synchrotron Radiation at Ultrahigh Laser Intensities

The role of ions in the energy absorption of a short and ultraintense laser pulse and in the synchrotron radiation generated by accelerated electrons is revisited. For laser intensities above 10(22) W/cm(2) and plasma densities more than 10 times the critical density, the ion-to-electron mass ratio strongly affects the energy repartition between the electrons, ions, and radiation. This phenomenon is studied with a one-dimensional relativistic particle-in-cell code, taking into account the radiation reaction force. The choice of the ion mass strongly affects the energy and angular distribution of the photon emission and the electron energy distribution. This effect may be important for laboratory modeling of radiation dominated relativistic astrophysical events. It can be verified in experiments with solid hydrogen targets.