Domain Selection

It is possible for rays to pass through domains in the geometry and to propagate in the void region outside these domains. Boundary conditions can be specified at any boundary, even at boundaries that are not adjacent to any domain in the geometry. This means that a ray can be reflected or absorbed by a surface in 3D or a line segment in 2D even if it isn’t attached to any other object. The ray tracing algorithm can also detect boundary interactions in any order, without this order being specified.

In the physics interface section, the is specified. This refractive index is used in any domains outside of the selection for the Geometrical Optics interface, as well as the void domain outside the geometry. It is a constant, scalar-valued quantity; thus, the refractive index outside the domain selection cannot depend on field variables such as temperature and cannot be a graded-index medium. The default refractive index of 1 represents a perfect vacuum.

Usually, the domain selection for the Geometrical Optics interface should include all objects that the rays might pass through. In a lens system, this would mean all lenses are included, but not necessarily the mount for these lenses. However, rays can also pass through the void region that surrounds the geometry.

A major advantage to excluding some domains from the selection for the physics interface is that these domains do not need to be meshed. However, these domains would still require a mesh if some other variables, like displacement and temperature, are solved for there. See Meshing Guidelines for Geometrical Optics Simulation for more details.

Note that some physics features require a domain mesh and will not function on domains outside the physics interface selection. This includes all types of Accumulator (Domain) feature, including the dedicated Ray Heat Source multiphysics feature.