Description

This example demonstrates the methodology of simulating fluorescence in FRED. Fluorescence is implemented through the wavelength attribute g_w associated with a scripted Scatter model. This attribute permits the wavelength of individual rays to be altered according to a user-programmed probability distribution. The ability to alter the wavelength assignment of individual rays is a key architectural feature of FRED, and the scripting language offers increased capability in wavelength manipulation. The power of FRED allows the user to carry out accurate color simulations for a wide range of physical phenomena; fluorescence being just one example.

The accompanying FRED file for this example, exampleFluorescenceInRhodamine6G.frd, can be found in the <install dir>\Resources\Samples\Tutorials & Examples\ directory.

Implementation

Setup

This simulation involves 0.486 mm light from an Ar+ ion laser incident upon a host layer impregnated with Rhodamine 6G dye.

Adding a source

Let this source have a Gaussian width of 0.075 mm and a wavelength of 0.486 mm.

Adding geometry

Add now a plane surface to represent the film of Rhodamine 6G:

Set the Coating to "Transmit", the Raytrace Control to "Allow All", and make the scattered rays have a different color.

Adding a scatter model

In order to complete the fluorescence surface definition, data for Rhodamine 6G must be inserted into a FRED scripted scatter model. FRED's Coating digitizer is convenient method of transforming graphic images into numerical data sets. Shown here is a bitmap image of the Rhodamine 6G emission spectra loaded into the digitizer.

The data from the digitized file can then processed and included in a scripted Scatter model shown here in part:

NOTE: Even though scripted scatter models are compiled before execution, it is recommended that datasets included within them should be kept compact so as to have minimal impact on raytrace speed.

This scatter model is assigned to the film surface and scatter into a small angle around specular is chosen as the Scatter Direction:

A detector surface is also created to catch the transmitted fluorescence and to accommodate an Analysis Surface.

Running the Simulation

The system model is shown here with an RGB rendering of the source color included:

The image below shows a Color Image calculation at the detector implemented with the Show in Visualization View feature of the Chart Viewer. This rendering is an RGB representation of the spectral content of fluorescence as described by the digitized data. Anyone who has operated a dye laser will recognize the familiar yellow color of this common laser dye.