I'm working on tracing the beam path of a HeNe laser through two prisms, and I'm stuck on trying to find the incident plane in which to use Snell's law.(adsbygoogle = window.adsbygoogle || []).push({});

Basically I have the equation of the angled surface of the prism, and I have the point where the beam intersects that plane. Now I need the normal vector to the surface at that intersection point, and then I can define the incident plane from the two vectors (the normal at that point and the vector that is the incident beam).

The problem I can't figure out is how to get thespecific vector perpendicular to the plane at the point of intersection. All the textbooks I've looked at have the "opposite" of what I need, because they assume I have both the normal and the point and want the plane, whereas I have the point and plane but want the normal. And I can't simply use that method to solve for the normal because it has a dot product that I can't undo.

Also, this is in cylindrical coordinates, and if I can avoid the conversion to Cartesian that would relieve at least some of my headache!

Any help or advice would be much appreciated.

Thank you

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# Ray Tracing

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