Photon Engineering FRED, Geometrical Construction

Stray Light/Ghost Analysis
*FRED* is designed for stray light and ghost analyses! In fact, *FRED* is the only commercial optical engineering software under active, continuous development for the specific needs of stray light analysts. *FRED's* stray light capabilities begin with “real world” scatter models. *FRED* has the following predefined bidirectional scatter distribution functions (BSDF):
• Lambertian • Harvey-Shack (smooth optical surface scatter) • Abg (smooth optical surface scatter) • Phong (cosn from specular; does not obey reciprocity but is common in computer graphics) • Diffuse black paint (scaleable generic diffuse black paint) • Particulate distributions (MIL-STD-1246, uniform, Gaussian) • Diffuse/Lorentzian binomial and polynomial models • Power Spectral Density (tabulated data) • K-correlation • Tabulated BSDF • User-defined scripting model (Note: Other models are in development.)
*FRED* has a curve-fitting feature for reducing measurements into diffuse/Lorentzian binomial and polynomial forms. This feature can optionally generate out-of-plane data and truncate minimum/maximum BSDF values. In its multiple regression mode, the feature can perform numerous fits to various orders and then sort according to average, minimum, maximum, and standard deviation errors. Any fitted model can be turned into a *FRED* scatter model. *FRED* supports “composite” scatter models composed of several individual models. This is useful when analyzing the effects of particulate and/or molecular contamination on optical surfaces with a given microroughness. For computational efficiency, *FRED* scatters light into user-specified “important” directions. These directions may be specified as • Angular spread about the specular direction• Angular spread about a given direction (direction is specified in any coordinate system) • Angular spread about a given point (point is specified in any coordinate system) • Towards a given entity • Towards a given closed curve • Towards a given ellipsoidal volume (volume is specified in any coordinate system) Multiple scatter directions may be assigned to each scattering surface. Any level of scatter/ghosts may be modeled and analyzed in *FRED. At the conclusion of a raytrace, FRED* can compile, rank, and display the stray light contributors in a convenient spreadsheet format. If requested, *FRED* can also list and optionally visualize the exact sequence of surface intersections that gives rise to a particular stray light path; this facilitates tracking down unexpected stray light paths. For more information on FRED's stray light capabilities read the Stray Light Application note here.	Tabbed output window for multiple angle 3D BSDF plots

	Stray light report for 2nd level scatter

	Scattered rays from primary and secondary mirrors, and main baffle