SDL/18-1237 Rev. A1695 North Research Park Way | North Logan, Utah 84341

info@sdl.usu.edu | www.sdl.usu.edu

DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

Because space-based sensors are becoming increasingly sensitive, telescope design requires greater attention to stray light performance. Radiation from off-axis sources, such as the Sun and Earth, enters the telescope aperture, where it scatters off system components and eventually reaches the focal plane. This stray light can degrade image quality and decrease the sensor’s ability to detect faint signals.

With decades of experience in stray light design, analysis, and testing, engineers at the Space Dynamics Laboratory (SDL) design optical systems with stray light rejection in mind and know how to resolve issues discovered during testing.

SERVICES

Design & Software Analysis• Assist with baffle design• Verify stray light design through modeling• Define scatter requirements for optical surfaces & coatings• Identify & fix issues in the design phase, before the instrument is builtTesting• Discover stray light paths missed in software analysis• Verify surface scatter properties• Test for opto-mechanical misalignments

STRAY LIGHTDesign, Analysis & Testing

During testing, a major stray light path was discovered in a sensor. Since stray light rejection was critical at small off-axis

source angles, a correction was applied. The before and after stray light performance is depicted above.

Ø Earth

Line of Sight

Object ofInterest

Field of View

Ø Sun

Original Instrument

1.E+00

1.E-01

1.E-02

1.E-03

1.E-04

1.E-05

1.E-06

1.E-07-5 -4 -3 -2 -1 0 54321

Off-Axis Angle (degrees)

Poin

t Sou

rce

Reje

ctio

n Ra

tio (P

SRR)

Modified Instrument

S PA C E D Y N A M I C S L A B O R AT O R Y

STRAY LIGHT Design, Analysis & Testing

SDL/18-1237 Rev. A

SDL is uniquely equipped to offer end-to-end stray light services, from initial design and software analysis to final testing. Using SDL's comprehensive services and state-of-the-art facility reduces the risk of experiencing a stray light problem once a system is operational.

DESIGN & SOFTWARE ANALYSIS

Features• Baffle design, including vane placement• Non-sequential ray tracing• Component- & system-level modeling & testing• Exact modeling of mechanical objects• Software tools: Zemax®, FRED™, MATLAB®• Scatter properties library for optical surfaces & coatings

- Optical surface roughness - Particulate contamination - Black paints

Types of Analysis• Stray light rejection performance estimation: Point Source

Transmission (PST), Normalize Detector Irradiance (NDI), etc.• Reverse ray tracing to identify critical surfaces & important

external stray light source locations in angle space• Thermal self-emission (TSE) to assess the instrument's

background thermal radiation

Instrument under test mounted on a rotary table.

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BLACK HOLE STRAY LIGHT MEASUREMENT FACILITY

High off-axis rejection systems are difficult to characterize terrestrially due to scattered light from the test setup. SDL’s large, specular black chamber dramatically reduces setup corruption by redirecting the scattered light away from the sensor’s entrance aperture.

This is SDL’s third-generation stray light measurement facility. SDL has tested numerous systems that have flown successfully in space.

Features• 100-foot dark cleanroom• System-level stray light measurements at ultraviolet, visible

& infrared wavelengths• Automated data collection• Data is reported in peak normalized form (PSRR) but can be

easily converted to other forms such as PSRR/µsr & NDI• Setup is transportable & accommodates sensor apertures

up to 24 inches

Test Setup

Demonstrated Performance

Black Chamber

Collimated Beam

Rotary Table Light Trap

Instrument

Source

Detector

The off-axis response of the instrument under test was measured nearly twelve orders of magnitude lower from the peak on-axis

response, demonstrating a very low noise floor.

1.E+00

1.E-04

1.E-08

1.E-02

1.E-06

1.E-10

1.E-01

1.E-05

1.E-09

1.E-03

1.E-07

1.E-111.E-12

0 20 40 6010 30 50 70

Off-Axis Angle (degrees)

Poin

t Sou

rce

Reje

ctio

n Ra

tio (P

SRR)

PSRR (θ) = ___________________Power Det (θ)

Power Det (θ = 0°)

Questions? SDL welcomes all inquiries. For more information about SDL’s stray light services, please contact:

John Stauder | Electro-Optical Engineer

435.713.3528

john.stauder@sdl.usu.edu