Compare DFT fields with and without device

[dalarev]

Hi, we are attempting to compare how a device impacts the natural divergence of a Gaussian beam. Our current setup is shown below:

Setup 1 is a Gaussian beam in vacuum. Looking at the DFT in the area shaded light blue nicely shows the natural divergence.

Setup 2 now includes a device bumped up against the source. We would like to probe the fields exiting the device and compare these against the natural divergence sans-device.

We are unclear of what two sims to run to get the appropriate reference fields. The two setups shown below have the same size DFT monitor but different model cell sizes. Direct comparison of the DFTs of these two sims doesn't seem correct because the scaling is different.

Any thoughts/guidance the community has are greatly appreciated.

Thanks!