Discussion Forum

Hello everyone, I'm a beginner user of COMSOL, and I'm stuck on a little problem. I'm using the "Electromagnetic Waves, Frequency Domain" interface to model an incident wave on a smooth surface, in order to calculate the transmittance and the reflectance of an N-BK7 glass. I followed the instructions of the "Plasmonic Wire Grating" tutorial, but my purpose is to compute the aforementioned quantities for different wavelengths. For this reason, I don't want the refractive index of my material to be constant: it must vary with the wavelength. Therefore, I created an analytic expression for the real part of the refractive index (which I named "n_NBK7"), as well as an interpolation function for the imaginary one (which I named "k_NBK7"). As concerns the air above my sample, I did the same thing with the real component (naming the function "n_air"), while I set the extinction coefficient to 0. I took all these relations from this link. My questions are the following: 1) In the study settings, I can make the wavelength sweep within the range of interest: how can I tell the software that the wavelength must be the input variable for my interpolation/analytic functions (i.e.: n_NBK7, k_NBK7 and n_air)? 2) In the Port boundary conditions, the ewfd interface needs to know the refractive index of the air (Port 1) and of the N-BK7 glass (Port 2), in order to compute the diffraction orders. Provided that I don't have a constant value for them (they depend on the wavelength), I want to call here the functions n_air and n_NBK7, respectively: is this feasible? Which is the correct syntax to do it? 3) If I understood correctly, the software computes the number of diffraction orders as a function of three parameters: the angle of incidence, the refractive index of the material (in my case, the N-BK7 glass) and the wavelength itself. This means that, during the sweep study that I'd like to run, the software should be able to adjust the number of Ports in order to compute the different diffraction orders: I mean, without requiring me to click manually on the "Compute Diffraction Orders" button (provided that it is disabled while the solver is running!). Am I reasoning right? Is there a way to automate the computation of diffraction orders?

Any help is very much appreciated! Thank you

PS: I'm going to attach the .mph file of my model, it could be useful to better understand my problem