Overlapping farfield profile with first gaussian mode
I am using nearfield to far-field projection in FDTD to calculate the far-field. Now, I am wondering how much the far-field profile overlaps with the first gaussian mode. I remember there was a similar discussion in the previous KB platform that was suggested a mode expansion monitor can be used for this purpose but I don't know how it works.
Apart from the above approach, I am thinking to plot the far-field in the cylindrical form (rather than ux,uy) and then compare the result with the basic Gaussian profile (in 3D). Unfortunately, I don't know if this approach works or not.
Can you please advise?