EDIT: Now that I have thought more I suppose this problem is a classical problem and should therefore be moved to that forum. Sorry for the mistake. Can this be moved? Hi I am working on a simulation trying to model light traveling through a periodic grating with subwavelength apertures. I am launching a Gaussian pulse at this structure and I would like to find which frequencies have the highest transmission. I have setup diagnostics that measure the poynting vector verse time of the incident and transmitted wave. Once I collect the data I use fast fourier transform in matlab and then get the power spectrum from the incident and transmitted wave. From my introductory waves course (I'm an undergrad) I remember that the transmission of a wave (lets just talk about a wave on a string) through a boundary is the square of the transmitted amplitude/square of the incident amplitude. So to find the transmission spectrum for my problem should I do something like what I would do with a wave on a string? I could divide the power spectrum of the transmitted wave by the power spectrum of the incident wave? I do not necessarily need a fully answer. It would be sufficient to just let me know if I am on the right or wrong track. Also can anyone recommend a book, website, or anything that would cover this material and is written at the undergrad/grad level? Thank you in advance for your help Note: I posted here because this forum cover computational physics but if there is a better place for this please let me know.