On Wed, 5 Jan 2011 15:36:44 +0800, Towhidur Razzak <towrazz...@gmail.com> wrote: > Dear all, > > I am trying to simulate light propagation through a gold > nano-aperture. But I have not yet obtain a model of gold which can reliably > model gold in MEEP at optical frequencies. > > It would be very helpful if any one of you can provide me with > the *omega, > gamma and sigma* parameters for gold. Thanks a lot in advance. > > *Towhid*
Hi, just for an idea, you could have a look at this paper Vial A, Grimault A-S, Macias D, Barchiesi D, de La Chapelle M. Improved analytical fit of gold dispersion: Application to the modeling of extinction spectra with a finite-difference time-domain method. Physical Review B. 71, 085416 (2005). For my calculations I have started out from that paper and made a few adjustments for getting a good fit between 400 nm and 900 nm: I am using the following Drude + two Lorentz terms Here in inverse seconds Drude term eps_infinity = 4.9752 omega_p = 2.1282e+15 gamma = 9.1942e+12 First Lorentz term Delta_epsilon= 0.28 Omega_L = 8.8712e+14 Gamma_L = 3.1691e+14 Second Lorentz term Delta_epsilon = 0.15158 Omega_L = 6.865e+14 Gamma_L = 1.7822e+14 With the following expressions for the Drude and Lorentz terms (in Matlab notation) epsilon_Drude = eps_infinity - omega_p^2./(f.*(f+1i*gamma)); epsilon_Lorentz = -Delta_epsilon*Omega_L^2./((f.^2-Omega_L^2)+1i*Gamma_L*f); (note that I use frequency, not angular frequency, but then I call the frequency constants "omega" just like in the Meep tutorial) Here is how they look scaled for a Meep length unit of 20 nm (define gold (make dielectric (epsilon 4.98) (E-polarizations (make polarizability (omega 1e-10) (gamma 6.13e-4) (sigma (* .142 .142 1e20))) (make polarizability (omega 0.0592) (gamma 0.0211) (sigma 1.76)) (make polarizability (omega 0.0458) (gamma 0.0119) (sigma 0.952)) ) )) Obviously with more Lorentz terms one can get an even better fit, but the calculations become longer. Please let me know if there are mistakes :-) Cheers, Giovanni -- ================================================ Giovanni Piredda Postdoc - AK Hartschuh Phone: ++49 - (0) 89/2180-77601 Fax.: ++49 – (0) 89/2180-77188 Room: E2.062 ---------------------------------------- Message sent by Cup Webmail (Roundcube) _______________________________________________ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
