How do I create an active material?

Date	Category
2023-12-05 19:31:06	Mediums

By default, Tidy3D will not allow medium specifications that give rise to active materials to avoid potential divergences. However, you can override this by setting the field allow_gain=True in any medium, e.g. tidy3d.Medium(permittivity=2.0, conductivity=-1.0, allow_gain=True).