Evolution of a short pulse using ray tracing

In a recent paper (Cairns and Fuchs 2010 Nucl. Fusion 80 095001) we have shown how the asymptotic method of stationary phase can be used to find the radiation pattern from an antenna in the far field region. The novel feature of this work is that it describes how to obtain the wave amplitude and phase in complex geometries where an explicit solution in terms of a phase integral is not available. Instead the necessary information is obtained from ray-tracing methods. Here we show how this method can be adapted to give the evolution of a short pulse in a plasma with arbitrary space and time dependence. Again the exact wave form of the pulse, including phase information, can be obtained from ray tracing. This provides a computationally simple way of calculating the behaviour of a short pulse that may be useful in studying some problems in laser-plasma interactions.