I made a 2D periodic structure similar to a plasmonic wire grating model. I want to study angle-dependent reflectance studies on this model. My material is a monolayer of Polystyrene (PS) spheres of diameter 1100 nm, on the silicon substrate. The simulation went well for the angle-dependent studies. But the comsol gives reflectance values in a symmetry fashion( Fig.2: if I give inc angle of 15 degrees, then reflectance is calculated in the 15 deg symmetry to the incident beam). The problem is that my material structure is acting like a 2D diffraction grating. Experimentally, I verified this by keeping the incident angle at 15 degrees and the detector angle varied from 30 to 75 degrees (with an optical goniometer setup) (Fig. 1 and 3). Doing this, I observed a shift in peak position in reflectance spectra (prismatic effect), which is in good agreement with the grating equation.

How to simulate this in the comsol, as if we vary the angle, the reflectance also collects symmetry to it, so it gives the interference aspect. But I want to keep the incident angle constant and collect the reflectance spectra at different angles, which will give the diffraction aspect (Fig. 1). Yes, I included the additional diffraction orders in the port. But it won't give the reflectance at different angles, as I said before.

So here the problem is. Keeping the inc angle constant (say 15 degrees), and collecting the reflectance spectra from 30 to 75 degrees ( as shown in Fig.3).

For reference, I attached the COMSOL (6.0) model file to this query.

Thank you.