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Assume system of charges
localised around a spatial position
.
The coupling to an electric field
within dipole approximation is then given by
|
|
|
(2.1) |
where
is the electric field at
.
The dipole approximation is valid if the spatial variation of
around
is
important only on length scales
with
, where
is the size of the volume in which the charges are localised. For a plane wave electric field with wave length
one would have
.
Tobias Brandes
2005-04-26