On Thu, 29 Mar 2012 02:33:07 +0800, 虞益挺 <yyt8...@gmail.com> wrote: > Hi Aaron, > >> Dear meep users,By the 3D simulation using MEEP, the transmission >> property at >> wavelengths 500~1000nm of 2D periodic array of Au nanoholes has now been >> achieved, from which an obvious SP resonant wavelength is observed. To >> theoretically verify the simulation results, the commonly used formula, >> lambda(SP) = a / sqrt ( i^2 + j^2 ) * sqrt ( epsilon(Au) * >> epsilon(dielectric) / >> ( >> > epsilon(Au) + epsilon(dielectric )?) ), is employed. (a is the array >> periodicity.)Then, a question occurs: for the theoretical calculation, >> how >> should I set the permittivity of gold? As it is a variable value >> depending >> on >> the wavelength, the permittivity of which wavelength is appropriate for >> this >> purpose??Any comments and suggestions are welcomed, and will be highly >> appreciated. Thanks in advance. >> >> >> If you only want to verify that you've matched the SP resonance >> condition, >> it's >> probably good enough to use the permittivity at a single wavelength. Of >> course, >> make sure that the theoretical value is the one meep is using. >> > > Thank you for your reply. > > I know your meaning, and that's exactly what I want to do now. However, the > question is: which single wavelength is appropriate for such purpose? > Because the permittivity of gold depends on the wavelength. I have tried a > series of calculations with different wavelengths from the aimed spectrum > (500~1000nm). The results for different wavelengths differ greatly. > > Looking forward to any further comments on this problem. > > Tony
It's a bit of time that I do not use MEEP, but I have got a hunch that you need to specify the dielectric function of gold in a range of frequencies using a Drude-Lorentz expansion - people that understand the physics and numerics better than I do could confirm or deny, but there is a problem with causality if using a negative epsilon without dispersion (with or without an imaginary part). I suggest you have a look at this http://ab-initio.mit.edu/wiki/index.php/Meep_Tutorial/Material_dispersion and this http://www.mail-archive.com/meep-discuss@ab-initio.mit.edu/msg03871.html Doing a Google search I have furthermore found this: which I did not check, so I cannot say it is completely correct, but looks helpful http://www.torrkish.com/index.php/research/34-meep/46-lorentz-drude-expansion-in-meep Giovanni ---------------------------------------- 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
