J.Kouba:

ANSYS is unit independent.  You can build models in micrometers or nanometers,
if you like.  There is no standard unit definition in ANSYS.

It is generally impossible to use FEA to simulate scattering problems in the
visible range, because the required element size is so small that the resulting
model is unsolvable.  It is unlikely that ANSYS is the correct tool for that
type of simulation.

Regards,
Dan Shaw