Simulation of photon acceleration in a plasma wake

The frequency shifting of an ultrashort (femtosecond) low intensity laser pulse in the presence of a plasma wave is investigated using particle simulations. One-dimensional simulations confirm the existence of photon trajectories similar to the trajectories of trapped or untrapped charged particles in a plasma wave. In the case when a plasma wake is produced by a relativistically intense laser pulse with a duration of the order of one plasma period, some full oscillations of the photon frequency take place only for the untrapped photons moving backward in the plasma wave frame before the intense laser pulse depletion due to the energy transfer to the plasma wake occurs. An analytical estimate of the probe pulse phase and frequency shift in two-dimensional (2-D) axially symmetrical plasma wake is performed. Axially symmetrical particle simulations in 2-D, with experimentally attainable parameters, display a frequency shift of the probe pulse of a few percent. In these analytical estimates and 2-D simulations special attention has been given to the modeling of the probe pulse optical collecting line that is typically used in plasma diagnostics. © 1999 American Institute of Physics.