Anomalous laser absorption in underdense solid targets by synchrotron emission

Summary form only given. Lasers with peak intensities of 10²² W/cm² have already been created [1] and within the next ten years the maximum attainable intensity is expected to increase to 10²⁴ W/cm² [2] . In this intensity regime electrons become ultra relativistic, with kinetic energies of hundreds of times their rest mass energy, ions become relativistic, low density solids become relativistically transparent and additional physical processes, such as synchrotron emission and even electron-positron pair production, become important. The combination of these effects means that the behaviour of systems above 10²³ W/cm² is qualitatively different to that at lower intensities. To model this regime one must consider these additional physical processes, and this has been done by modifying the PIC code EPOCH [3] to include a semiclassical model for photon production by synchrotron emission and then the conversion of these photons into electron-positron pairs by the Breit-Wheeler process.