Kaushik,
You will find it both ways in various texts and the reason for the
difference is a little subtle. The value of a propagating wave changes with
time and distance traveled. Since in the time domain the value is periodic
(sinusoidal) it is usually supressed.
If you assume an exp^(+ j omega t) time dependance, for a lossy
material, the imaginary part of refractive index for a lossy material will
be negative.
If you assume an exp(- j omega t) time dependance, the imaginary part
of refractive index for a lossy material will be positive.
If you look closely in the texts, the authors should state what version
of time depedence they have chosen to use (either is valid) and they should
use the approproate sign.
I hope this helps.
Good Luck!
Neal
On Tue, Feb 16, 2010 at 2:36 PM, <[email protected]> wrote:
> In the meep website, it is said that an complex epsilon of 3.4 + 0.101i at
> a
> frequency 0.42 (in your Meep units)
> can be modeled as (make medium (epsilon 3.4) (D-conductivity (/ (* 2 pi
> 0.42
> 0.101) 3.4)))
>
> However, in most of the text book the complex epsilon is defined as
>
> epsilon = Re(epsilon) - Im(epsilon)*i
>
> I want to know if this is just a matter of sign convention?
> Meep reference says that the imaginary part of epsilon is associated with
> absorption loss in the material if it is positive. However, in the text
> books
> the imaginary part of epsilon is associated with absorption loss if it is
> negative.
>
> Thank you very much,
> Kaushik
>
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