Hi everybody, Wen-Yu,
I have been confused by the explanation of the website myself. But from what I
have found, I feel that you can just fit the following equation to your data:
einf+(sigma*omega^2)/(omega^2-f^2-i*gamma*f)
While fitting, I use the frequency definition from the “Meep Introduction”, f=a
/ lambda. So for a wavelength of 1550 nm, I get a frequency of 100 nm / 1550 nm
= f = 0.06452
I put the parameters I find immediately into MEEP. Without any multiplying or
dividing by 2 x pi.
I wrote the script listed below to verify my Lorentz model and from what it
tells me, my metal is modeled the way I want (@ w=0.06452, epsilon is -126.86 +
3.54I).
I hope it is of any help to you (and that I didn’t make any mistakes).
Best regards,
Milan
(reset-meep)
(define silver
(make dielectric
(epsilon 2.6043207)
(polarizations
(make
polarizability (omega 0.0063593931) (gamma 0.0016545937) (sigma 13198))
)
)
)
(set! force-complex-fields? true)
(set! eps-averaging? false)
(set! geometry-lattice
(make lattice
(size 5 5 5)
)
)
(set! geometry
(list
(make block
(center 0 0 0)
(size infinity infinity
infinity)
(material silver)
)
)
)
(set! resolution 1)
(init-fields)
; My lattice constant is 100 nm, so my frequency of interest is 100 nm / 1550
nm = 0.0645.
(print "Complex epsilon: "(meep-fields-analytic-chi1 fields Ex 0.0645 (vector3
0 0 0)) ", frequency: 0.0645\n")
(quit)
From: [email protected]
[mailto:[email protected]] On Behalf Of ???
Sent: dinsdag 3 augustus 2010 4:22
To: [email protected]
Subject: [Meep-discuss] Unit transformation of dispersion parameters
Dear all
I have a question about the content of “Meep Tutorial/Material dispersion”.
http://ab-initio.mit.edu/wiki/index.php?title=Meep_Tutorial/Material_dispersion&oldid=3762
There are two dielectric functions listed there, one is a function of w,
another is a function of f. As my realization, w=f in Meep, ex: f=1 then w=1.
The two functions should be identical. Why is the gamma divided by 2*pi in
function of f? If gamma needs this adjustment, omega has the same unit with
gamma, why is it not divided by 2*pi?
I am confused about unit transformation. If I find a dispersion relation in SI
unit as:
epsilon(f)= W + (X*Y^2) / (Y^2 - f^2 - i*f*Z) (SI unit)
f is the frequency (Hertz)
W, X (No unit)
Y, Z, (Hertz)
I define Meep unit length = a (meter), speed of light c = 3e8 (m/s)
The frequency unit is c/a (Hertz). So I define the parameters in Meep code as
epsilon W
omega (/ Y (/ c a))
gamma (/ Z (/ c a))
sigma X
Is the transformation correct?
Any help will be appreciated.
Thanks a lot!
Wen-Yu Chen
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