Handbook of Optical Sensors

656

Handbook of Optical Sensors

From Maxwell equations, we have,

nn

2

=⇒=±εµ εµ, and by physical reasons,

Veselago showed that we need to have (Veselago 1968)

n =

+⇐

>>

−⇐

<<











εµ

εµ

εµ

εµ

00

00

and

and

(21.6)

erefore, for (ε < 0, µ < 0), the refractive index is negative.

e second quadrant involves (ε < 0, µ > 0), from where n takes imaginary values

and propagation is not allowed (besides evanescent eld). e line µ = 1 includes the

region where materials support conventional plasmonics, most notably gold and silver

at optical frequencies, which have specic values for ε that are wavelength dependent

but essentially determined by their intrinsic atomic str ...