Material Discontinuity

The node is the default boundary feature on all boundaries. It computes the initial direction of the refracted ray using Snell’s law. If extra degrees of freedom have been allocated for secondary rays, a reflected ray is also produced. If the incident ray undergoes total internal reflection, no refracted ray is produced and no secondary rays are needed to release the reflected ray.

If is set to , , , or in the physics interface section, the feature computes the radii of curvature and the Stokes parameters of the reflected and refracted rays.

	The maximum number of reflected rays can be controlled via the Maximum number of secondary rays text field, which is found under the Ray Release and Propagation section for the physics interface.

The Accumulator (Boundary) subnode is available from the context menu (right-click the parent node) or from the toolbar, menu. The Thin Dielectric Film subnode is also available if the following conditions are met:

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One of the following options is selected from the list in the physics interface section: , , , or .

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One of the following options is selected from the on boundary list in the section: or .

This section is available if is set to , , , or under the section for the physics interface. Use the options in this section to add thin dielectric layers to the boundary between the media. These thicknesses of these layers should be small relative to the coherence length of the radiation, and is often comparable in length scale to the free-space wavelength.

Select an option from the list — (the default), , , , , , or .

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If is selected, rays undergo reflection and refraction at the boundary as if there were no dielectric films present.

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If is selected, apply thin dielectric layers to the by adding one or more Thin Dielectric Film subnodes. If multiple thin films are added to a single surface, they are arranged in the same order as the corresponding subnodes in the Model Builder.

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If is selected, apply thin dielectric layers to the by adding one or more Thin Dielectric Film subnodes. Also enter a value or expression for the N (dimensionless). The default value is 3. It is possible to choose which individual layers are included in the repeating unit cell and which layers only appear once in the settings for the subnodes. Use this option to specify periodic arrangements of dielectric layers for structures such as dielectric mirrors.

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If is selected, enter a value or expression for the λ0 (SI unit: m). The default value is 660 nm. Enter a value or expression for the θi (SI unit: rad). The default value is 0. Select an option from the list — (the default) or . Select an option from the list — (the default) or .

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If is selected, enter a value or expression for the n (dimensionless). The default value is 1. Then enter a value or expression for the t (SI unit: m). The default value is 1 μm.

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If is selected, select an option from the list — (the default) or . Select an option from the list — (the default) or . In addition, enter values or expressions for the following:

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If is selected, select an option from the list — (the default) or . Select an option from the list — (the default) or . In addition, enter values or expressions for the following:

The option automatically computes the refractive index and thickness of a single-layer dielectric coating to yield zero reflectance for the specified free-space wavelength, polarization, and angle of incidence. Similarly, the options and automatically compute the thickness of a dielectric layer of the specified refractive index to yield the specified reflectance or transmittance.

If the material properties on either side of the material discontinuity differ, rays with the same angle of incidence will be subjected to different reflectances, depending on which domain they approach the boundary from. Use the list to determine whether the specified reflectance applies to rays incident from the upside or downside of the boundary. It is convenient to select the check box (see below) when identifying the upside and downside of the boundary, since the boundary normal points from the upside to the downside.

This section is available if is set to , , , or under the section for the physics interface.

Enter a Ith (SI unit: W/m2). The default is 1·10-3 W/m2. If the interaction of a ray with a material discontinuity would create a reflected ray of intensity less than the threshold intensity, the release of this reflected ray is suppressed. This prevents an arbitrarily large number of degrees of freedom from being used to model the propagation of rays of exponentially decreasing intensity. When a nonzero threshold intensity is specified, some small decreases in the total energy of the system may be observed if the release of low-intensity secondary rays is suppressed.

If an Auxiliary Dependent Variable has been added to the model then there is an option to reinitialize the values of auxiliary dependent variables for the refracted ray. These setting are the same as in the New Value of Auxiliary Dependent Variables section for the Wall feature.

If an Auxiliary Dependent Variable has been added to the model then there is an option to reinitialize the values of auxiliary dependent variables for the reflected ray. These setting are the same as in the New Value of Auxiliary Dependent Variables section for the Wall feature.

Select the check box to view the boundary normal in the window.

	Visualization of the boundary normal is important when adding multiple Thin Dielectric Film subnodes, since the thin films are oriented from the upside of the boundary to the downside in the same order as displayed in the Model Builder.

If the check box is selected in the physics interface section, select the check box to set the optical path length of reflected and refracted rays to 0. Otherwise both the reflected and refracted ray inherit the optical path length of the incident ray.