The frequency shifting of an ultrashort (femtosecond) low intensity laser p
ulse in the presence of a plasma wave is investigated using particle simula
tions. One-dimensional simulations confirm the existence of photon trajecto
ries 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 relativis
tically intense laser pulse with a duration of the order of one plasma peri
od, some full oscillations of the photon frequency take place only for the
untrapped photons moving backward in the plasma wave frame before the inten
se laser pulse depletion due to the energy transfer to the plasma wake occu
rs. An analytical estimate of the probe pulse phase and frequency shift in
two-dimensional (2-D) axially symmetrical plasma wake is performed. Axialll
ir 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 bee
n given to the modeling of the probe pulse optical collecting line that is
typically used in plasma diagnostics. (C) 1999 American Institute of Physic
s. [S1070-664X(99)03102-X].