DOUBLE-CROSSING MODE CONVERSION IN NONUNIFORM MEDIA

A new type of mode conversion between two linear waves in a nonuniform medium is investigated. Single-crossing conversion occurs when a ray of one wave crosses transversely the dispersion manifold of another wa ve. Double-crossing mode conversion theory describes when the ray punc tures the dispersion manifold twice due to ray curvature. To study thi s new process, a one dimensionally nonuniform background medium is con sidered, which gives rise to four scenarios. These scenarios are disti nguished on the basis of whether the two waves have equal or opposite energy signs, and whether they are copropagating or counterpropagating . Using modular-eikonal theory (suitable for multiple crossings), each scenario is first studied analytically by constructing an S-matrix re lation between the outgoing and incoming asymptotic wave amplitudes. T he analytical results are then compared with numerical results and exc ellent agreement is found. (C) 1998 American Institute of Physics.