This model correctly provides the following typical pattern when you have two crossed polarizer and a slightly diverging beam.:)

A discussion about this dll:

Straylight in VR Pancake | Zemax Community

Hi Sebastian,

Unfortunately, the source code for this DLL cannot be shared, although I do think it’s actually quite simple that I just follow the paper I mentioned in the post.

But anyway I actually think this model is only ideal and I would suggest you use the static link to have a more realistic model when you start to do a realistic design. In this workflow, you can use Lumerical STACK to calculate the response accurately for any incident angle and polarization. You can find more detail in the following link.

Lumerical Sub-wavelength Model: Usage in Zemax OpticStudio – Ansys Optics

On the other hand, for the purpose of accurately modeling of components like grating, wave plate, or polarizer, I would suggest to use diffraction DLL instead of scattering DLL. The problem with scattering is it cannot control the power ratio between reflection and transmission, while diffraction DLL has more control to this.

Please let me know if you still have any questions. Thank you.