• Description
For users of the Ray Optics Module, COMSOL Multiphysics® version 5.2a brings the ability to model ray tracing outside the geometry, a new plot type for measuring monochromatic aberrations, improvements to the Ray Trajectories plot, and more. Review all of the Ray Optics Module updates in more detail below.

Ray Propagation Outside the Geometry

When tracing rays through a lens system, you no longer need to add an air or vacuum domain to encompass the rays. The rays can be released and can propagate outside the geometry and in domains that are not meshed, as long as these regions are homogeneous (nongraded). With this new capability, the Material Discontinuity boundary condition can now be used on exterior boundaries, instead of the Wall condition, to allow rays to refract into or out of the meshed domains. Most of the examples in the Application Library have been updated with this feature.

When modeling, specify the Refractive index of exterior domains feature in the Geometrical Optics interface Settings window. When rays propagate outside the geometry or in domains that are not in the selection list for the Geometrical Optics interface, this value of the refractive index will be used. The rays can still interact with boundaries in the geometry, even if they are not adjacent to any meshed domains. However, the boundaries themselves must be meshed. The meshing of boundaries is handled automatically when using the default mesh settings.

A collimated beam is focused by a convex lens. The rays can propagate in the lens and in the region outside the geometry where no mesh is defined. The color expression on the rays is based on their intensity, while the color of the mesh is proportional to the element size.
A collimated beam is focused by a convex lens. The rays can propagate in the lens and in the region outside the geometry where no mesh is defined. The color expression on the rays is based on their intensity, while the color of the mesh is proportional to the element size.

Optical Aberration Plot

The new Optical Aberration plot type is dedicated to measuring monochromatic aberrations. These plots compute the optical path difference between incident rays as they converge toward a focal point, then fit the optical path differences to a basis of Zernike polynomials. You can plot any linear combination of the Zernike polynomials, multiplied by the computed Zernike coefficients. You can also generate a table of Zernike coefficients using the Aberration Evaluation feature.
Zernike polynomials up to the fifth order, plotted on a unit circle.
Zernike polynomials up to the fifth order, plotted on a unit circle.

Improved Ray Trajectories Plot

The Ray Trajectories plot type now automatically includes a number of extra points, in addition to the solution at the stored time steps or optical path length increments. Usually, these extra points are located where rays are reflected or refracted at boundaries. With the extra points, the Ray Trajectories plot type is now improved and conveys far more information than before, even if the number of stored time steps or optical path length increments are very small.

Comparison of the Ray Trajectories plot type in the Czerny-Turner Monochromator model with the same number of stored solution times in COMSOL Multiphysics® version 5.2 as compared to COMSOL Multiphysics® version 5.2a.
Comparison of the Ray Trajectories plot type in the Czerny-Turner Monochromator model with the same number of stored solution times in COMSOL Multiphysics® version 5.2 as compared to COMSOL Multiphysics® version 5.2a.

New Options for Cone-Based Release

Several new options are available when releasing rays with a conical distribution of initial directions. You can release rays with a uniform density in wave vector space, so that each ray subtends the same solid angle. Alternatively, you can specify the density of rays in the polar and azimuthal directions separately. Built-in options are also available to release marginal rays only, with or without an axial ray.

There are now four options when releasing rays with a conical distribution.
There are now four options when releasing rays with a conical distribution.

Renamed Options for Intensity Computation

The Intensity Computation list options in the the Geometrical Optics interface Settings window have been given new more intuitive names.

Option Name in Version 5.2 Option Name in Version 5.2a
Using principal curvatures Compute intensity
Using principal curvatures and ray power Compute intensity and power
Using curvature tensor Compute intensity in graded media
Using curvature tensor and ray power Compute intensity and power in graded media

Updated Tutorial Model: Solar Dish Receiver

The Solar Dish Receiver tutorial model has been updated to include two sets of benchmark data.

A paraboloidal dish concentrator can focus incident solar radiation onto a target or cavity receiver, resulting in very high local heat fluxes. This can be used to generate steam, which can be used to power a generator; or hydrogen, which can be used directly as a fuel source. In some applications, the uniformity of the flux on the surface of the cavity receiver has a significant effect on efficiency. In the example, solar radiation is reflected by the concentrator toward a small area in the focal plane, where a cavity receiver can be positioned.

Of particular interest in evaluating the performance of solar collector-receiver systems is the concentration ratio, defined as the ratio of the incident flux to the ambient solar flux.

The model evaluates the concentration ratio in the focal plane of a paraboloidal solar concentrator for two sets of assumptions. First, the paraboloidal reflector is treated as a perfectly smooth, nonabsorbing reflector. Second, the effects of surface roughness, absorption, and sunshape are taken into account. Both of the two studies compute the resulting concentration ratio in the focal plane of the paraboloidal dish and these results are compared against published values.

Application Library path: Ray_\Optics_\Module/Industrial_\Applications/solar_\dish_\receiver

The Solar Dish Receiver tutorial model shows the data comparison between the results and published values for an ideal reflector (top left) and a reflector when taking surface roughness, absorption, and solar limb darkening into account (top right). The 2D results for each case are also presented (bottom).
The Solar Dish Receiver tutorial model shows the data comparison between the results and published values for an ideal reflector (top left) and a reflector when taking surface roughness, absorption, and solar limb darkening into account (top right). The 2D results for each case are also presented (bottom).