Intensity, Polarization, and Power
Ray intensity is computed using a variant of the Stokes–Mueller calculus in which both the amplitude and polarization are tracked along individual rays.
List of Available Settings
To decide whether intensity is computed, select an option from the Intensity Computation list. The following options are available.
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None: Does not compute any intensity information.
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Compute intensity: Solves for intensity, which typically increases as rays are focused and decreases as they diverge. Also affected by reflection, refraction, and attenuating media. Only valid when the media are homogeneous.
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Compute power: Solves for power, which is unaffected by the convergence or divergence of rays but is still affected by reflection, refraction, and attenuating media. Can be used to compute heat source terms in attenuating domains or heat flux terms on absorbing boundaries that the rays hit.
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Compute intensity and power: Combines the capabilities of Compute intensity and Compute power, at the cost of a few extra degrees of freedom per ray.
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Compute intensity in graded media: Similar to Compute intensity, but is also applicable to graded-index media. The tradeoff is that this method is slower and less accurate for homogeneous media.
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Compute intensity and power in graded media: Similar to Compute intensity in graded media but can also be used to generate heat sources in attenuating domains and heat flux terms at boundaries.
Handling Polarization
Whenever intensity or power is solved for, the polarization of every ray is known. Rays can have any degree of polarization, ranging from 0 (unpolarized) to 1 (fully polarized) and anything in between. When rays have some degree of polarization, they can be linearly, elliptically, or circularly polarized.
When rays are reflected and refracted at boundaries, the intensity, polarization, and power are updated based on the Fresnel equations, which automatically take the polarization direction into account.
The polarization is determined based on the Stokes parameters, which are allocated as extra degrees of freedom along each ray. For more information, see The Stokes Parameters in the Theory for the Geometrical Optics Interface chapter.
 
In the following examples, ray polarization is manipulated in an instructive way:
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Total Internal Reflection Thin-Film Achromatic Phase Shifter (TIRTF APS): Application Library path Ray_Optics_Module/Prisms_and_Coatings/achromatic_phase_shifter
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Linear Wave Retarder: Application Library path Ray_Optics_Module/Tutorials/linear_wave_retarder
Wavefront Curvature
When the ray intensity is solved for, it increases where rays are focused together and decreases where rays diverge. This is accomplished by treating each ray as a wavefront and storing its principal radii of curvature as extra degrees of freedom. In this way, all released rays are treated as points on planar, spherical, or ellipsoid-shaped wavefronts.
For more information on wavefront radii of curvature and their effect on intensity, see Principal Radii of Curvature in the Theory for the Geometrical Optics Interface chapter.
Computing Deposited Ray Power
The options Compute power, Compute intensity and power, and Compute intensity and power in graded media all allow heat sources to be defined on domains or boundaries. As rays propagate through an attenuating medium — that is, a medium where the refractive index is complex-valued — some energy is lost from the ray. The corresponding heat source on the surrounding domain can be computed using either the Deposited Ray Power (Boundary) subnode or the Ray Heat Source multiphysics node. A Ray Heat Source node is automatically created when you have selected The Ray Heating Interface in the Model Wizard. The heat generated as rays propagate in an attenuating medium can be used to define a heat source in the Heat Transfer in Solids interface or another physics interface that computes a temperature field.
Thermally Induced Focal Shift in High-Power Laser Focusing Systems: Application Library path Ray_Optics_Module/Structural_Thermal_Optical_Performance_Analysis/thermally_induced_focal_shift
Total Power Transmitted and Reflected at Gratings
The Grating feature is used to model the transmission and reflection of rays at diffraction gratings. It includes a Diffraction Order (Grating) subnode to specify which diffraction orders to release. When the ray power is solved for, the Store total transmitted power and Store total reflected power check boxes are shown in the Grating settings window. Selecting either of these check boxes causes an auxiliary dependent variable to be declared, storing the total power of the transmitted and reflected rays of all diffraction orders.
Diffraction Grating: Application Library path Ray_Optics_Module/Verification_Examples/diffraction_grating