Figure 1.
Illustration of the focusing function F(x, xR, t), which focuses at xR. For x at and above |${{\partial \mathbb {D}}_R}$| it is purely upgoing. For x in the half-space below |${{\partial \mathbb {D}}_R}$| it is a complex wave field. The near-horizontal arrows in the thin layer illustrate tunnelling evanescent waves.
