This command creates a new Raytrace Control specification in the document. Raytrace controls are applied surfaces in the model as non-optical properties (i.e. specific to FRED, not to the surface physics) and govern the type of ray interactions that are allowed to occur upon intersection with any surface that has been assigned the raytrace control. The point of this property is to allow the user some control over the efficiency of the raytrace. For example, if the physical properties of a surface can allow both a specular reflection and a specular transmission but the analysis being performed only requires transmitted ray information, then a custom raytrace control for this surface which suppresses the generation of the specularly reflected ray can be used to prevent unnecessary computation and memory usage. The raytrace control has the ability to specify the following items: Ray Power Cutoff Thresholds Indicates the minimum absolute or relative power that a ray must have in order to continue being raytraced. Allowed Ray Operations Indicates the types of components that can be generated at a given surface (i.e. specular reflection, transmitted scatter, etc.). Intersection Count Cutoffs Indicates the number of total surface intersections or consecutive intersections with the same surface that will cause a ray to stop being raytraced. Ancestry Level Cutoffs Indicates how many times a given ray is allowed to split due to surface specular or scatter properties. Parent Ray Specifier Indicates the component of a ray splitting interface which will have its ancestry level maintained.
This command can be accessed in the following ways: •Menu > Create > New Raytrace Control •Ctrl + Alt + R •Toolbar button: •On the Raytrace Properties folder in the object tree view, right-click and select "Create a New Raytrace Control Set..." from the list menu.
An absorbed ray is created at a surface where the following two conditions are met:
The absorbed ray has power equal to the power difference between rays exiting a surface and the incident ray that created them. Note that under these conditions a raytrace control set which prevents rays from being created at a surface could result in absorbed rays.
Absorbed rays are physical rays that behave just like any other ray generated at a surface. As such, they can be used for analyses such as irradiance, spot diagrams, etc. These rays offer a convenient way to show the spatial distribution of absorbed power on a surface. A new ray selection criteria has been added to the analysis surface ray selection list allowing for filtering of absorbed rays. Absorbed rays are marked as having completed their raytrace and will not propagate away from the surface during the raytrace.
In order for FRED's absorbed rays concept to accurately reflect the physical absorption that would occur at a surface intersection, the model needs to be set up physically. That is to say, all ray types that could be physically generated should be allowed to propagate away from the interface with surface coatings, scatter models and materials that accurately represent the real system.
The absolute power cutoff value is a hard limit. That is, rays with power below this value are halted and will not propagate further. The relative power cutoff value is determined at the surface intersection and not with respect to the source power. Mathematically; Pout / Pin > Prelative. The ratio of the output ray's power to the input ray's power must be greater than the relative power cutoff threshold specification.
Raytracing in Monte-Carlo mode with TIR There is a subtle behavior that can occur when a raytrace control has both the Monte-Carlo (1 ray only) option selected as the Parent Ray Specifier and the Specular Total Internal Refl option toggled in the Allowed Ray Operations. This subtlety has to do with the order of operations that occurs within the raytrace engine itself.
•If the TIR option is disabled and Monte-Carlo mode is used, the specularly reflected ray is temporarily created during the ray interaction stage of the raytrace but is thrown away before the Monte-Carlo dice roll occurs so that the reflected component will never be selected. •If the TIR option is active and Monte-Carlo mode is used, the specularly reflected ray is temporarily created but NOT thrown away before the Monte-Carlo dice roll occurs. At the time of the dice roll, the specularly reflected ray exists and can therefore be selected as part of the Monte-Carlo process. Furthermore, the specularly reflected component can exist even when the incident ray is not in a TIR condition. In this case, the specularly reflected component will usually have significantly higher power than any scattered components that may also be generated and will therefore usually be selected in the Monte-Carlo process
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