FRED Stray Light FRED A software tool for

FRED Stray Light FRED: A software tool for modern engineering

FRED What is FRED? Overview • Comprehensive opto-mechanical systems design analysis tool • Stray light analysis (scatter and ghosting) • Coherent beam propagation • Imaging system design and photo-realistic rendering • Virtual prototyping • Opto-mechanical systems debugging (Forensic Optics) • Thermal self-emission analysis • Illumination design • Tolerancing, fabrication and testing • Both sequential and non-sequential raytracing modes • Multi-variable optimization capability

FRED What is FRED? FRED can be used in virtually every step of the design process. 1. Initial proof of concept using catalog parts 2. Integration of optical and CAD designs 3. Full analysis of a virtual prototype including scatter, coatings, dispersion, absorption, volume scatter, diffraction, thermal emission, source characteristics… 4. Quickly manipulate model parameters for tolerance analyses 5. Integration with vendor catalogs for manufacturing or system debugging Overview FRED 1 2 3 4 5 Concept Design Analysis Tolerancing Manufacture

FRED Sources of Stray Light Common stray light sources include: • Diffraction • Specular ghosts • Grating effects from manufacturing • Scatter from structures • Particulate contamination • Thermal self-emission • Background sources • Bulk material effects

FRED Effects of Stray Light • Stray light = performance reduction • Stray light should be accounted for during design • Correcting stray light requires knowledge of the source • FRED provides engineers a toolbox for stray light analysis

FRED Surface Scatter Models • Lambertian • Harvey-Shack • ABg • Phong • Diffuse Black Paint • Particulates (Mie) • Diffuse Polynomial • Diffuse Binomial • Tabulated BSDF • Tabulated PSD • K-correlation • User-scripted (BASIC) Stray Light Tools

FRED Stray Light Tools Scatter Importance Sampling • Scatter rays only into regions of interest • Saves time by raytracing efficiently • Correctly accounts for ray directions Importance Sampling Options • Angular spread about specular • Angular spread about a given direction • Angular spread about a given point • Towards an entity • Through a closed curve • Through a volume

FRED Stray Light Tools Volume Scattering Stray light effects can come from bulk material volume scatter Implemented as “random walk” using a mean free scatter distance Translucent materials, suspended particulates, etc.

FRED Stray Light Tools Surface Raytrace Controls • Allows specific interaction types: scatter, transmission, reflection etc. • Set ray power cutoff thresholds • Specify number of allowed ray splits due to scatter or specular • Precise control over model tracing • Applied to individual surfaces

FRED Stray Light Tools Raypaths and Stray Light Report • Keeps track of ray intersection paths • Sorts raypaths by scatter and specular • Reports scatter/ghost level • Provides information on ray count, path power, scatter/ghost surfaces • Paths can be marked for sequential tracing • Raypaths can be redrawn to the 3 D view

FRED Diffraction • Grating structures • Linear • XY Polynomial with aspheric terms • Diffraction from apertures, edges, slits, etc. when tracing coherent rays Stray Light Tools

FRED BASIC Compiler and Scripting FRED’s fully integrated BASIC scripting language allows for custom calculations such as thermal self-emission and PST Stray Light Tools

FRED Ghosting in a Double Gauss Lens Stray Light Example • 10 degree off axis angle • Uncoated lenses • Allow only first order paths straylight_ghost. Image. frd

FRED Ghosting in a Double Gauss Lens • Allow all raytrace paths • Irradiance distribution shows ghost image Stray Light Example

FRED Ghosting in a Double Gauss Lens Stray Light Example • Use FRED’s Stray Light Report to identify the ghost path(s) • Ghost is caused by a reflection from surface 10

FRED Ghosting in a Double Gauss Lens Stray Light Example • Apply an AR coating to surface 10 • Ghost image power reduced by an order of magnitude!

FRED Stray Light Summary • FRED provides engineers with a comprehensive toolbox for stray light analysis • Using FRED during system design can be invaluable • Models are easily constructed in the 3 D cad environment with realistic opto -mechanical properties • FRED’s built in compiled scripting language adds flexibility for customizable analyses