Optical Aberration
The Optical Aberration () plot shows various types of monochromatic aberration that arise when electromagnetic rays are focused by a system of lenses and mirrors. It is available with a 2D Plot Group, and you select it from the More Ray Optics Plots submenu. Add Height Expression and Transparency or Visual Effects (only if Height Expression is used) subnodes if required.
An Intersection Point 3D dataset (see Intersection Point 2D and Intersection Point 3D) pointing to a Ray (Dataset) dataset must be used. The dataset must point to an instance of the Geometrical Optics interface in which the optical path length is computed.
In addition, in the Settings window for the Intersection Point 3D dataset, Hemisphere must be selected from the Surface type list. The Center of the hemisphere corresponds to the focus, and the Axis direction points from the focus toward the center of the exit pupil in the focusing system. Some of these details can be set up automatically using the settings and buttons available in the Focal Plane Orientation section.
Go to Common Results Node Settings for links to information about these sections: Data, Title, Range, Coloring and Style, and Inherit Style. For Optical Aberration plots, only Intersection Point 3D datasets are allowed as inputs.
The Optical Aberration plot is available with the Ray Optics Module.
Filters
Use the options in the Filters section to exclude some rays from the calculation of the Zernike coefficients.
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Select the Filter by wavelength check box to exclude all rays except those of a specified vacuum wavelength. If this check box is selected, enter a Wavelength (default: 632.8 nm) and a Tolerance (default: 1 nm). If the difference between the specified wavelength and the vacuum wavelength of a ray exceeds this tolerance, then the ray will be ignored.
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Select the Filter by release feature index check box to exclude all rays except those released by a specific physics feature. Then enter an integer value for the index; the default is 1. This field is 1-indexed, meaning that 1 corresponds to the first ray release feature, 2 is the second ray release feature, and so on.
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Select the Filter by number of reflections check box to include rays only if they have reflected a specified number of times. Then enter an integer for the number of reflections; the default is 0. For this option to work correctly, it is necessary to select the Count reflections check box in the settings for the Geometrical Optics interface, before running the study.
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Select the Filter by additional logical expression check box to include rays if they satisfy another user-defined expression. The expression is considered to be true if it returns a nonzero value. The default expression is 1, which would cause all rays to be included.
Focal Plane Orientation
The settings in the Focal Plane Orientation section are used to define the position of the focus and the direction of the nominal optical axis that intersects this focus.
Select an option from the Normal to focal plane list: Direction based (the default), Position based, or User defined.
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For Direction based, the normal to the focal plane is the average ray direction. This average is taken over all rays that satisfy the filter criteria given by the Filters section above.
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For Position based, the normal to the focal plane is determined such that the ray positions are as close to the plane as possible. If the rays are stopped at a curved surface, the normal computed in this way may differ significantly from the surface normal.
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For User defined, enter values or expressions for the normal vector components directly. By default, the z-axis is used.
Enter a value or expression for the Reference hemisphere radius (SI unit: m). The default is 50 mm. When automatically generating an Intersection Point 3D dataset for the Gaussian reference hemisphere, this value is copied to the dataset settings. As a general rule, this value should be much larger than the RMS spot size but must be smaller than the back focal length of the optical system.
The Create Reference Hemisphere Dataset and Recompute Reference Hemisphere Dataset buttons can be used to automatically generate or update an Intersection Point 3D () dataset from which the Gaussian reference hemisphere is defined. The hemisphere is centered at a location where the rms spot size is minimized. The hemisphere axis should point backward along the nominal optical axis through the focal point.
Before clicking Create Focal Plane Dataset, make sure that the Dataset is either a Ray dataset () or From parent (if the parent is a Ray dataset). If rays are released at multiple field angles and you want to compute the Zernike coefficients associated with one of these fields, first select the Filter by release feature index check box in the Filters section.
Before clicking Recompute Reference Hemisphere Dataset, make sure that the Dataset is already an Intersection Point 3D dataset.
When clicking either button, the Intersection Point 3D dataset is then created (or updated) to define the intersection points with a hemisphere. The center of the hemisphere is positioned as close as possible to the RMS focus.
The button commands to create or update an Intersection Point 3D dataset indicating the reference hemisphere can also be accessed from the physics API. In a model method or in a model Java® file, you can use commands such as
ResultFeature plot = model.result("pg1").feature("oab1");
plot.runCommand("createReferenceHemisphereDataset");
plot.runCommand("recomputeReferenceHemisphereDataset");
Zernike Polynomials
Select the Length unit in which the weighted Zernike polynomials will be plotted. The default is the micron (μm). This input is disabled if the model is dimensionless.
The optical path difference among all rays that pass through the exit pupil is computed. Then a linear least-squares fit is used to express the optical path difference as a linear combination of a standard set of orthogonal polynomials on the unit circle, called Zernike polynomials. The polynomials are scaled by the coefficients that are computed by the least-squares fit, called the Zernike coefficients.
Select a Maximum polynomial order: 2, 3, 4, or 5 (the default).
Select an option from the Terms to include list: All, All higher-order terms, or Select individual terms:
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If All is selected, all Zernike polynomials up to the specified Maximum polynomial order are included in the plot.
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If All higher-order terms is selected, all Zernike polynomials up to the specified Maximum polynomial order are included in the plot, except for the terms of order 0 and 1. These terms indicate misalignment or misplacement of lenses within an optical system and are less useful for measuring lens quality.
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If Select individual terms is selected, check boxes appear for all Zernike polynomials. The common names of the polynomials are included where applicable. Select or clear the check boxes to determine which terms should be included in the plot. You can also use the Select All and Clear All buttons to quickly select or clear all of these check boxes at the same time.
Enter a Number of grid points, which must be an integer between 100 and 1,000,000. Increasing the number of grid points increases the number of evaluations of the Zernike polynomials on the unit circle; this improves the quality of the plot but does not affect the calculation of the Zernike coefficients.
A list of Zernike polynomials and their derivation, properties, and references are included in the Ray Optics Modeling chapter of the Ray Optics Module User’s Guide.
Position
Specify the position of the center of the unit circle. The default center location is the origin, (0,0). By assigning nonzero components to the center location it is possible to view multiple types of optical aberration in the Graphics window side-by-side.
For an example of the use of Optical Aberration plots: Double Gauss Lens: Application Library path Ray_Optics_Module/Lenses_Cameras_and_Telescopes/double_gauss_lens.