  Using complex plane analysis we show that left-handed slab may support either
leaky slab waves, which are backward because of negative refraction, or leaky
surface waves, which are backward or forward depending on the propagation
direction of the surface wave itself. Moreover, there is a general connection
between the reflection coefficient of the left-handed slab and the one of the
corresponding right-handed slab (with opposite permittivity and permeability)
so that leaky slab modes are excited for the same angle of incidence of the
impinging beam for both structures. Many negative giant lateral shifts can be
explained by the excitation of these leaky modes.
