Scattering Boundary
The scattering boundary can be used to scatter rays in reflection and transmission from any boundary using one of several scattering models:
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Diffuse scattering will scatter rays according to Lambert’s cosine law. That is, the probability of a ray propagating in a given direction within a solid angle dω is given by cos θ dω where θ is the angle between the direction of the ray and the wall normal.
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Isotropic scattering will cause rays to be randomly scattered in all directions.
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Surface slope error will cause the surface normal to be perturbed by a random angle sampled from a Rayleigh distribution based on the value or expression for the Surface slope error σ (SI unit: rad). The default is 1 mrad.
Rays can be released from a Scattering Boundary in both reflection and transmission. That is, the options for which Rays to release include Reflected and transmitted (the default), Reflected, or Transmitted.
If both reflected and transmitted rays are chosen, then, unless total internal reflections occurs, the primary rays are expected to be transmitted.
Wavelength or Frequency Reinitialization
This section is available when the distribution of released rays is either Polychromatic, specify vacuum wavelength, or Polychromatic, specify frequency. If activated the wavelength or frequency of a ray can be reset as it interacts with the selected boundaries. The new wavelength or frequency distribution function can be:
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 None – the wavelength or frequency is set to a user defined expression.
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 Normal – the wavelength or frequency distribution will follow a normal (Gaussian) distribution with a user defined Mean vacuum wavelength or Mean frequency μ, and a Vacuum wavelength standard deviation or Frequency standard deviation σ.
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 Lognormal – the wavelength or frequency distribution will follow a log normal (Gaussian) distribution with a user defined Mean vacuum wavelength or Mean frequency μ, and a Vacuum wavelength standard deviation or Frequency standard deviation σ
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 Uniform – the wavelength or frequency will be drawn from interval specified by the Minimum vacuum wavelength λ0,min or Minimum frequency νmin and the Maximum vacuum wavelength λ0,max or Maximum frequency νmax
New Values of Auxiliary Dependent Variables
See Wall for information on the section New Value of Auxiliary Dependent Variables.
Advanced Settings
All of the scattering models (and wavelength or frequency reinitialization) generate random numbers. The option to enter an Additional input argument to random number generator i (dimensionless, default 1) is possible if in the Advance Settings section for the Geometrical Optics interface, the Arguments for random number generation setting is set to User defined. The Advanced Settings section is also shown if the Compute optical path length check box is selected under the physics interface Additional Variables section. Select the Reset optical path length check box to set the optical path length to 0 when a ray interacts with a scattering boundary.
Surface Scattering Theory