Coherent Field Synthesis
It is possible to create a set of coherent rays from an imported complex field, using Gabor synthesis. The new rayset is a collection of Gaussian beamlets whose amplitude, phase and directional distribution are determined by the complex field characteristics as well as the area and spatial resolution over which the original field was calculated.
This tool is available under the Raytrace menu item.
When selecting this option, the following dialog is displayed. Note the following:
- The location / orientation of the synthesized set of rays will be defined in the section at the top. They are not linked to a specific source or a surface.
- The data can be imported via right-clicking on the grid and selecting "Read From File..." (more on the format below).
- There is an option on the right to either replace any rays currently in memory, or to append to them.
- The section in the middle defines the synthesis parameters. For most cases, there is a simple recipe to follow as described below
Importing vector fields
Files of FRED's *.fgd and *.dat formats can be imported into the coherent scalar field synthesis dialog by right mouse clicking in the scalar field sample grid and selecting "Read From File". If the field is not generated by FRED, and needs to be created by an external program / script, then please view the "Grid Data Object Format" in the FRED Help for the format.
If the field is generated by FRED, then it can either be the resulting file from a Coherent Scalar Field Analysis or a Coherent Vector Field Analysis.
If a vector field file is chosen for import, FRED will prompt the user to choose either the X or Y field component for synthesis during import. If it is necessary to synthesize both components, then this needs to be done in two steps using the "Append Rays" option.
Synthesis Parameters
The specific definition of these parameters can be found in the Help, but a simple recipe that works for most cases is as follows:
- Semi-Ape: Set this to the maximum allowed value
- Max Ray Shift: Set this to 1
- Max Ray Angle: Set this to be large enough to fill the next optic.
Example
The associated FRED file can be downloaded here.
This simple example uses a coherent field created by a TE01 Hermite mode plus a TM10 Hermite mode, as shown here. The Coherent Vector Field of these two sources will be calculated and saved as a fgd file. Then the Coherent Field Synthesis will be used to import this field and create a new set of rays.
Left: Ex Field of the TE01 Mode. Middle: Ey Field of the TM10 Mode: Right: the combined Irradiance.
Saving the Coherent Vector field
- Create Rays
- Analyses => Coherent Vector Field saving an ARN.
- Save the ARN to fgd file.
- Delete the rays
Synthesizing the X Component
- Open Raytrace => Coherent Field Synthesis...
- Right-click on the grid and select Read From File..., select the fgd file saved in Step 3 above.
- Select to import X component
- Adjust the synthesis parameters as per above
- Click Create Rays
Synthesizing the Y Component
- Right-click again on the grid and import the file again via the Read From File... option
- Select the Y Component
- Make sure that the "Append Rays" radio button is selected, and click Create Rays.
Checking the Imported Field
An Analysis Surface can be used to calculate the Coherent Vector Field or Irradiance and check the validity of the synthesis.
Tracing the rays through the system
A very important note is that after this process is completed, the rays exist in memory (and are not tied to a specific source). Therefore to trace these rays one of the "Trace Existing" options need to be used.
