Ray Tracing

the method you choose for specifying the ellipse. The graphical display gives helpful feedback on the polarization state you have specified.

Surface Sources

A surface source emits rays in a prescribed angular distribution from one or more surfaces of a solid objects in the Model. Surface sources are defined as Surface Properties and are described in Chapter 4. See “Surface Source Properties” on page 4.12

Importance Sampling from Surface Sources Standard Expert

In order to increase sampling in a particular direction, you can use importance sampling with surface sources. This is analogous to importance sampling for scattered rays. The importance sampling setup that you enter for scattered light is also used for surface sources.

With importance sampling specified for a surface that is a source, emitted rays will be generated in a direction as specified by the importance sampling data. The flux of the rays is determined by the angular emission profile of the source, the solid angle subtended by the importance sampling target, and the flux or irradiance of the surface source. See “Importance Sampling” on page 4.22

File Sources

A file containing ray data can be inserted into a TracePro model and used as a source. A File Source consists of 7 columns of tabular data, XYZ starting positions for each ray, XYZ direction vectors for each ray, and a flux.

The File Source concept provides the capability to:

1.incorporate measured source distribution data from Radiant Imaging into a TracePro model,

2.“continue” a raytrace by using data incident on one surface to be used as a source in another raytrace or another model, and

3.create a source from either theoretical or measured data in another application (e.g. - text editor or spreadsheet).

No matter which method was used to create the File Source, the source is inserted into the model the same way.

Creating a File Source from Radiant Imaging Data

Radiant Imaging, Inc. (Duvall, Washington, USA) provides measurement services and data for light sources. Lambda Research collaborates with Radiant Imaging to let you import measurement data and use it within TracePro to simulate real light sources.

To create a TracePro File Source using Radiant Imaging data, perform the following steps:

1. Start ProSource, available from Radiant Imaging.

1.Open a Radiant Imaging database file (.mdb extension).

2.Enter output options in the Ray Generation dialog.

3.Select the TracePro output type and file name with a *.dat or *.txt extension.

Defining Sources

4. Press Generate Rays to create the TracePro File Source.

For more information on ProSource, contact Radiant Imaging, http://www.radimg.com/.

Creating a File Source from an Incident Ray Table

A File Source can be created from an Incident Ray Table in TracePro. Some examples of how this capability can be used are as follows:

•model an LED, insert a dummy object as a “target”, perform a raytrace, save the Incident Ray Table as a File Source, insert the File Source of the LED into other models, the File Source for the LED can be repeatedly inserted into several locations in the same model to create an LED Array

•for performing a Stray Light Analysis on a complex optical system, a dummy object can be inserted as a “target” at any point along the optical path - the Incident Rays on the “target” can be saved as a File Source, and the File Source can be inserted into the model to be used as a source while analyzing/ modifying the objects at the end of the optical path - the raytrace times can be decreased considerably when the first group of objects are omitted from the raytrace

To create the File Source:

1.select the surface in the Model Window or the System Tree

2.select Analysis|Incident Ray Table to view the Incident Ray Table

3.with the Incident Ray table as the active window, select File|Save As, choose the file format as *.txt, and check the box for “Export to Source File format”

For more information on Incident Ray Tables see the section titled “Incident Ray Table” on page 6.38.

Creating a File Source from Theoretical or Measured Data

A File Source must have the appropriate header information to be recognized by TracePro. (See the TracePro Help topic “File Source Format” for further information) The easiest way to create a file with the proper format and header information is to make a simple TracePro model and follow the steps above to Create a File Source from an Incident Ray Table. Next, open the newly created File Source in a text editor or a spreadsheet application. Delete the existing data, then Calculate, cut-and-paste, or input the theoretical or measured data for the source. Save the file as a text file.

Insert Source

To use the File Source in a TracePro model, select Define|File Source to open the File Source dialog box as shown in Figure 5.13. You can also open the dialog from the Source tab in the System Tree by Right-Clicking and selecting

Define|File Source.

When the File Source dialog is opened you can create a new file source by doing the following:

Ray Tracing

FIGURE 5.13 - File Source dialog box.

1.Enter a name to identify the source.

2.Enter the name of a txt, dat, src or ray file by either typing it into the cell or by browsing to it using the browse button on the File Source dialog box.

3.Enter the Center Position of the source.

4.Enter the Rotation angles.

5.Enter a value for Trace n-th ray.

6.Enter a scale factor for the flux.

7.Select a color.

If the source contains wavelengths, they will be displayed, along with the total flux for the wavelength and a weight of 1. You can enter weight values to change the spectral balance of the source. If the source contains no wavelengths, you can enter you own by typing in a wavelength (in μm) and clicking Add (or pressing Enter). You can delete wavelengths by selecting them in the table and clicking Delete.

Note: By selecting the Center Position as the origin (0, 0, 0), and the Rotation Angles as 0, the rays will be emitted from the XYZ location specified in the File Source, and will propagate in the direction of the XYZ direction vectors specified in the File Source. Selection of any other Center Position or Rotation Angle will

Defining Sources

effectively “add an offset” to the positions and/or direction vectors specified in the File Source.

You can change to radians by clicking the in Degrees button, which toggles between radians and degrees. Selecting the button changes the name on the button to in Radians. You can change back to degrees by clicking the button again.

After specifying the source, click Insert to create the source.

To modify an existing source, first select it in the Source Tree and select Define|File Source (or simply double-click on the name of the source in the Source Tree). Change entries as desired and click Modify to modify the source.

Capability to “trace every nth ray”

TracePro allows you to trace a subset of the rays in a File Source using the “Trace n-th ray” field. The Total Rays are displayed in the File Source dialog to facilitate this data entry. For a Source File with 10,000 rays, entering “5” for Trace n-th ray will trace 10,000/5 = 2000 rays.

Capability to scale flux

The total flux from the File Source can be scaled using the “Scale flux” field in the File Source dialog. The total Flux of the source is displayed in the File Source dialog to facilitate this data entry. For a Source File emitting 5W, entering “1.05” for “Scale Flux” will increase the flux of each ray such that the Total Flux emitted will now be 5.25W.

Modify the File Source

Changing Source Location and Orientation

To move and rotate the source, you can either use the Move Source and Rotate Source options or open the File Source dialog either from the Source tab in the System Tree or by using Define|File Source. For the latter method, select the source to change and update the values. For the former method see “Orienting and Selecting Sources” on page 5.26. When a file source is selected in the Source tab in the System Tree, a sphere is drawn in the Model window showing the location source’s center and maximum radius of the rays starting points from the center. The sphere is drawn in the color selected in the File Source dialog.

Changing File Source Data

Source files may be created by the Radiant Imaging program ProSource, by the optional TracePro Bitmap module or by hand. Both ASCII and Binary formats are supported. For more detailed information on the File Source Data formats, please refer to the TracePro on-line help: Contents(tab)|Define Commands|File

Source|Source File Format.

There may be times where you want to modify data within a Source File, but that file is used in multiple TracePro models. The next time one of those models is opened and a raytrace is performed, you might be surprised to obtain a different analysis result, not realizing that the Source File had been modified. TracePro warns of this condition. When the TracePro oml file is saved, the last modified date of any Source Files are stored as part of the oml file. The next time that TracePro oml file is opened, TracePro checks to see if any of the Source Files