137967.fig.001a
(a)
137967.fig.001b
(b)
137967.fig.001c
(c)
Figure 1: Schematic diagram illustrating (a) internal ( ) and (b) external ( ) refraction in the laboratory frame. The transparency condition ( ) is shown in part (c). External refraction regimes tend to be highly angular and cannot be adequately described by the paraxial approximation.