Stray Light

BRO's Stray Light Tutorial gives participants the knowledge and skills they need to do stray light analysis with ASAP, BRO's Advanced Systems Analysis Program. The class covers scattered light, ghost reflections, thermal emission in infrared systems, edge scatter and wide-angle edge diffraction. Participants balance theory with hands-on experience by applying each lesson in a series of practice sessions.

Course Overview

The course covers standard methods for finding and correcting stray light problems in existing systems, as well as designing systems with low stray light levels. Information on the scatter characteristics of optical and mechanical surfaces is presented. A detailed study of how to efficiently perform quantitative stray light calculations is done, which includes in-depth coverage of the ASAP commands used for stray light analysis and the interactions between them. Analytic formulas that are useful for performing top-level stray light estimates and spot checks on quantitative stray light calculations are also presented.


  • Completion of BRO's Introductory ASAP Tutorial or equivalent knowledge and experience
  • Ability to build and view elementary systems with surface and edge-based entities
  • Ability to define and trace rays from various sources, and perform power, irradiance, and intensity calculations
  • Ability to comfortably write and run command scripts and macros
  • Experience in the use of the CONSIDER and SELECT commands in ASAP to isolate objects and rays

Course Outline

  • What is stray light, why is it important, and where does it come from?
  • Stray light design procedures
  • The importance and use of stops
  • Elementary front baffle and sunshade design
  • Performing ghost calculations
  • Design techniques for reducing stray light from ghosts
  • Introduction to stray light calculations
  • Elementary radiometry and radiation transfer
  • Introduction to scatter characteristics of surfaces
  • Characteristics of scatter measurements
  • Using the ASAP BRDF fitting utility
  • Quantitative descriptions of stray light performance
  • Top-level stray light calculations with a pocket calculator
  • ASAP scatter commands and their use
  • Scatter from contaminated mirrors and lenses
  • Evaluating the accuracy of stray light calculations
  • Calculating ghost irradiance
  • Stray light calculations for infrared systems
  • Calculation of stray light from edges
  • Stray light considerations for spectrographs, laser systems, coronagraphs, and chopped systems
  • Scatter from anisotropic surfaces

* If you are unsure that you meet these requirements, please speak with the instructor prior to enrolling in the class.

This Advanced Tutorial is a three-day course limited to 16 participants.