In the conventional geometric-optic approximation to wave propagation excited by a source of finite extent, each source point emits rays that transport wave energy along well-defined trajectories, but with transport properties exhibiting singularities in caustic regions where the cross section of ray bundles vanishes. In the first-order quasi-particle approximation the extended source is viewed as a phase space distribution of point quasi-particles whose space-time dependent kinetic properties such as density, average velocity, etc., provide nonsingular measures of the space-time transport of amplitude, wave number, frequency, etc., of the wave train modulation even in caustic regions. The range of ap- plicability of the quasi-particle method is examined in terms of relative space-time scales characteristic of the excitation and medium.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.