Determining pathlength of light within diamond sample in NSC mode

Question

Hi, I’m trying to make a NSC 2D plot where I sweep the incidence angle of light going into a cuboid sample and use the NSRA operand to determine the path length. This is an example using a 2 degree incidence angle:

However, there are some instances where the NSRA operand gives an error (‘Geometry error. Run the NSC Ray Trace tool for more information.) I think the issue might be when the incidence light and output light are collinear with each other (so they overlap, essentially) but I might also be wrong. An example of this is when the incidence light is 0 degrees.

What happens then is when I try to make a NSC 2D plot, there are certain step counts that are invalid, causing the whole graph to give an error:

Is there a way to ignore these instances when making the 2D plot?

Kevin Scales · Accepted Answer

Some operands have the option to ignore errors, but NSRA only works with a single ray, so if it can’t trace then it has nothing to work with.

From your image, it looks like the problem is that your ray is striking the vertex. This is going to be an error, since there is not unique surface normal so there’s no way to calculate the angle of refraction or reflection. The ray overlapping itself is not a problem, and if it had reflected off a mirror at normal incidence, it would have worked fine.

I think in this instance, the best option is to adjust your universal plot so the exact center ray striking the vertex never gets called. Maybe using an even number of rays where they approach but skip the center would work out.

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