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Birefringent Types

时间:2024/5/25 23:21:49   作者:郑士利   来源:正势利   阅读:39   评论:0




The birefringent type is used to define birefringent properties of solids made from uniaxial anisotropic materials, such as calcite.



Mode This control allows selection of which rays are actually traced. The distribution of energy does not change with this setting, and energy assigned to rays that are not traced are placed in the “lost energy (thresholds)” sum. Either ordinary or extraordinary rays, or both, may be traced. Waveplate Mode traces the energy along the path of the ordinary ray, however, the extraordinary electric field is also propagated with the ray, and the total electric field will be phase rotated by the differential index in the ordinary and extraordinary directions.


Reflections This control determines whether refracted or reflected rays, or both, will be traced. Note rays that TIR at a surface are considered reflected rays.


Ax/Ay/Az The dimensionless components of the uniaxial crystal orientation vector in object local coordinates. These coordinates define the orientation of the axis of symmetry for the media. Internally, the coordinates are normalized to a magnitude of unity. If all three terms are zero, the orientation used is (0, 0, 1).


Axis Length The length in lens units of the crystal axis drawn on layout plots. Use a value of zero to not draw the crystal axis.

Birefringence is ignored unless both polarization and ray splitting are on. If birefringence is ignored, the media acts like an isotropic media whose index is defined by the material associated with the volume. If birefringence is considered, the material associated with the object defines the “ordinary” refractive index. The “extraordinary” refractive index is defined by the material whose name is determined by appending “-E” to the ordinary material name. For example, if the object material name is CALCITE, then the extraordinary material must be named CALCITE-E. If both material names are not found in the current glass catalogs, an error is issued. If the material is defined as either a table or model glass, the extraordinary and ordinary indices are set to the same value and the media is effectively not birefringent.

When a ray strikes a boundary where either the incident or substrate media (or both) is anisotropic, as many as four separate rays are computed - two for ghost reflection and two for refraction. In each direction, there may be a separate ordinary and extraordinary ray. The ordinary ray carries the portion of the electric field that lies orthogonal to the plane that contains the direction of propagation and the crystal axis vector, while the extraordinary ray carries the electric field that lies in that same plane. If the media the rays are traveling in is isotropic (such as the ghost reflection off of a birefringent object) then the ordinary and extraordinary rays are combined into a single ray for convenience, as the energy propagates along the same path in this case.

Although there are important differences between the non-sequential and the sequential model for birefringent media in OpticStudio, most of the discussion about the birefringent media itself is common to both models. This discussion is found in “Birefringent In and Birefringent Out”.

Birefringent media may not also be gradient index or use bulk scattering, and may not be diffractive or scatter rays at the media boundaries. Simple ray splitting is not supported for birefringent media. Sources may not be placed inside birefringent media.

Note that birefringence in non-sequential mode needs ray splitting turned on to work, which is not allowed in mixed/hybrid mode. If a birefringent material is defined in NSC group in a mixed mode system, rays will always follow the ordinary path no matter what mode is chosen for the birefringent object.




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