I am trying to model a focused azimuthally polarized beam incident on a SiO2 substrate. I previously modeled a focused azimuthally-polarized beam propagating in air in Lumerical FDTD using the “Import Source” feature. Now I am trying to model the same beam propagating in air, but impinging on a SiO2 substrate. When I introduce the SiO2 substrate into the simulation, instead of forming a nice focused magnetic field at the focus of the beam, the beam reflects off the SiO2 substrate and produces a standing wave pattern. I have tried to remove this effect by drastically increasing the number of PML layers on the boundary conditions and moving the source very far from the SiO2 substrate, but neither of these has given rise to a nice focused beam. Could you please help me in figuring out how to model a focused azimuthally polarized beam impinging on a SiO2 substrate?
I am attaching the fsp file for the beam without the substrate (FocusedAPbeam-2000nm.fsp) and the fsp file for the beam with the substrate (FocusedAPbeam-2000nm-SiO2substrate.fsp).
FocusedAPbeam-2000nm.fsp (6.3 MB)
Thank you for any help you can provide.