THz plasmons in GaAs nanowires

THz scattering in GaAs nanowires.docx (362.5 KB)

I am looking at scattering cross-sections for GaAs nanowires in the 0.1 - 7THz frequency range.
I looked at these simulations 4 years back, and I was seeing a shift in the peak of the scattering cross section as we vary the nanowire length. I was able to look at peak shifts for nanowire length shifts of 2 microns. The contour plots of how the scattering cross section varies with nanowire length are in the attached document. Our experimental data also shows similar shifts in the peak position with varying nanowire length.

I am now trying to reproduce similar plots with the current Lumerical FDTD version. But my simulation can not sense the nanowire size variation. What I see is that I get similar scattering data for nanowire lengths upto 5 micron. Then the scattering data changes for 10 micron length and remains the same till lengths of 20 microns. Then it changes again, and remains the same for 30 - 60 microns. The base simulation file is attached.Template1e18.fsp (371.7 KB)

I tried a few different mesh settings, but could not resolve the issue. Can someone help me with resolving this? What has changed from the old version, and why cant I resolve 2 micron changes in nanowire length, as I used to be able to do?