Try the original double slit experiment from home with these 3D printed slits and a common laser pointer!

Go as detailed as your printer can handle. Getting the slits nice and clean will give you a much better effect. Thickness of the panel around the slits should also be as minimal as possible without losing definition to the actual slits.

I printed mine at 0.1mm layer height and 100% infill which worked well for my Ender 3 V3 SE. I'm hoping higher end printers will make even nicer slits.

See the Youtube short video here.