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Description
Note: This Source Primitive type is provided for legacy purposes. When possible, the Laser Diode Beam (coherent) type of Source Primitive should be used.
The Astigmatic Gaussian Beam type of Source Primitive generates a diverging set of rays that emanate from separate X and Y focii along the z-axis. The diverging set of rays is apodized so that the irradiance profile of the beam is Gaussian. If the divergence angles in the X and Y directions are different, then the resulting irradiance profile of the source will have different spatial widths in X and Y. In general, this source model will only give accurate results outside of the Rayleigh range of the source and for far-field divergence angles less than 5 degrees. Source verification should be performed at at least two planes beyond the Rayleigh distance in order verify the beam widths at these locations.
Navigation
This feature can be accessed in the following ways:
•Menu > Create > Source Primitive > Astigmatic Gaussian Beam
•Right mouse click on the Optical Sources folder, select Create New Source Primitive > Astigmatic Gaussian Beam
•Toolbar button: 
Controls
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Control
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Inputs / Description
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Defaults
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Logical Parent
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Read-only. Specifies the source's parent node on the tree.
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Optical Sources
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Name
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Name of the source as it will appear on the tree view.
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Astigmatic Gaussian Beam N
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Description
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Description string that will be visible on the tree view.
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Parameter Attributes
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0
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Total power of the source specified in Watts.
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1.0
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1
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Number of sample points across the X dimension. Generally, more sample points are required as the angular divergence and astigmatism of the source increases.
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11
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2
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Number of sample points across the Y dimension. Generally, more sample points are required as the angular divergence and astigmatism of the source increases.
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11
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3
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Far field divergence full angle in the X direction, specified in degrees.
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10
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4
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Far field divergence full angle in the Y direction, specified in degrees.
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10
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5
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Axial separation of the X and Y focii. The separation is symmetric about the source origin.
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0.01
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6
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Specifies the distance from the source origin at which the wavefront synthesized using the X and Y sampling defined by parameters 1 and 2. Generally, this distance should be larger than the Rayleigh range of the source and may be chosen as the distance between the source and the first optical element.
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0.2
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Wavelength Attributes
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Single
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The coherent field will be generated at the requested wavelength. The wavelength units are microns.
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Default wavelength Preference
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Source Draw Color
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The ray positions and ray trajectories will be rendered with the selected color.
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Polarization
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Polarization
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If checked, polarization data for the rays is maintained and stored.
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Unchecked
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Handedness
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Sets the handedness of the polarization state (relevant for non-linear polarization states). If the ray is propagating towards you, the electric field vector rotates in a clockwise direction for Right handedness and counter-clockwise for Left handedness.
Note that for linear polarization, the application of Left or Right handedness is arbitrary. The user may find that the UI display switches handedness depending on the angle of the linear polarization state entered, but this will have no impact on the resulting representation of the linear state.
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Right
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Ellipticity
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Sets the ellipticity of the polarization state, 0 represents linear polarization and 1 represents circular.
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0
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Angle
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Sets the angle of the polarization relative to the X axis.
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90
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OK
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Accept settings and close dialog box.
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Cancel
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Discard settings and close dialog box.
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Apply
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Accept settings and keep dialog box open.
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Help
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Access this Help page.
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Application Notes
Divergence angle limitations
The construction of this source is only suitable for far-field divergence angles < 5 degrees and is primarily used for backward compatibility. When possible, the Laser Diode Beam (coherent) type Source Primitive should be used.
When working with large divergence angles the number of X and Y sampling points will need to be increased to ensure accurate sampling of the angular space. However, it is strongly suggested that the user verify that the power contained in the source after ray creation is correct and that the field distribution at various planes give the expected distribution based on the gaussian beam equations. The following steps should be taken to verify that the power contained in the source after ray creation is correct:
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1.
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Add an analysis surface at the source location with a reasonable grid sampling (ex. 101 x 101) whose X and Y extents are 10 - 100 times larger than the beamwaists.
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2.
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Create the source rays by going to Menu > Raytrace > Create All Source Rays.
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3.
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Calculate the irradiance using the analysis surface in (1) above.
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4.
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Verify that the integrated power printed to the output window matches the power requested in the source definition. If this power does not match the requested source power, proceed to steps (5) and (6) below.
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5.
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Delete the rays and increase the X and Y sampling of the source node (parameters 1 and 2 of the Source Primitive).
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6.
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Repeat steps 2 - 5 until the integrated power matches the power requested in the source dialog box.
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Note that increasing the sampling results in more rays and longer calculation times. Users should determine the minimum number of sample points resulting in total power accuracy in order to be as time-efficient as possible during source creation.
Users are also cautioned to check the beam parameters at some distance away from the source position to verify that the beam being created has the expected parameters. Gaussian beam parameters are discussed on the Laser Beam (00 mode) help topic.
Related Topics
Source Primitives
Plane Wave (coherent)
Point Source (coherent)
Laser Beam (00 mode)
Laser Diode Beam (coherent)
M-Squared Laser Beam (coherent)
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