ZEMAX: Software For Optical System Design
| Ray Splitting |
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When light travels from one refractive index to another, a partial reflection occurs because the speed of light is different in the two media. This means that some fraction of the energy is transmitted, and some fraction is reflected. Additionally, some energy may be lost (absorbed) especially if the interface has a metallic coating on it. Partial reflections are sometimes known as Fresnel reflections. ZEMAX has sophisticated models of Fresnel reflections from bare and coated surfaces, including complex multi-layer coatings. See the Polarization and Thin-Film Coatings section for more details. When a ray intersects the surface of an object, ZEMAX computes the fraction of energy transmitted, reflected and absorbed at the interface. It can then split the ray into two: a reflected and a transmitted ray, with the correct relative energy. Here is an example of a beamsplitter cube:
In this case, approximately 1% of the energy is reflected by the MgF2-coated N-BK7 prism faces, and approximately 50% is reflected/transmissted by the coating on the hypoteneuse face where the two prisms touch. New rays (called 'child' rays) are launched to take this energy away, and so a complete picture of where the energy goes in the system is produced. Ray splitting is a vital technology for understanding stray light in optical systems and in many illumination systems. ZEMAx's modeling of ray-splitting is comprehensive. ZEMAX also supports a probailistic model of ray splitting, called simple splitting, in addition to its comprehensive model. This simpler model can be advantageous in illumination systems like brightness enhancement filters.
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