How to model laser beam ?

I want to model a laser beam and simulate its reflection/diffraction/scattering with medium/geometry I designed.

which behaviour of beam (wave/particle) do you think should be chosen / does it make a difference ?

which software best fits for this application ? I am currently on FEKO and I can't figure out how to model laser beam. A narrow width grid antenna at PHz frequency ?

Any ideas are appreciated.