Wave Propagation in Linear Media | re-examined

2.1 Superluminal wave propagation
a
!c1=
"r1; r1
c
a p "r1 r1
d
"r2; r2
!c2 =
c
a p "r2 r2
"r1; r1
Figure 2.2: Wave guide discussed by Martin and Landauer. The dielectrics and the centre frequency
of the pulse must satisfy !c1 d) is proportional to the input pulse
(x; t) / (x , d , tc;0) ; (2.6)
if the pulse was initially centred about x = 0. This means that the pulse seems to arrive
behind the barrier at a time t (x , d)=c, without spending any time in the barrier itself.
The derivation was based on a causal theory. However they appeared to be uncertain about
the interpretation and called the result `an apparent violation of causality'.
Soon afterwards, Hass and Busch [63] came up with a discussion of the same model. They
focused on the e ect of an increasing barrier thickness by considering only the di erence
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