Advanced deflectometry methods for industrial application

Heejoo Choi, Hyukmo Kang, Yiyang Huang, Mina Yoo, Henry Quach, John Kam, Daewook Kim

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Deflectometry is a versatile optical testing tool used in various fields, from astronomy to industrial applications, due to its non-null testing capability which facilitates precise measurement despite challenging optical surfaces and system layout constraints. In this manuscript, we present novel variational advancements to traditional deflectometry, towards universal functionality and system friendliness. Traditional dark-field illumination is an inspection technique that is sometimes used to detect particles on a specular surface. Problems arise in its repeatability, as an intensity-based measurement is vulnerably dependent on the testing conditions of time, limiting its ability to be used in automated fashion. The first advancement leverages phase algorithms commonly seen in deflectometry; by adding a secondary light source (normal to the surface) and modulating each source's intensity with a time-varying sinusoid. The phase-based information has a higher sensitivity to the light scattered from a defect producing a more robust computational image process method that is now insensitive to the environment. The second advancement is an alignment method to obtain lower-order shape. While deflectometry proves effective in measuring mid-to-high frequency surface shape, it faces challenges when assessing low-order shape measurements like power, astigmatism, and coma due to relative position and alignment error between the unit under test (UUT) and the deflectometry system. To avert the necessity of additional instruments like a coordinate measuring machine, laser trackers, or interferometers, we leveraged computational fiducials and sensitivity matrices to identify and address misalignments effectively. With enhanced capabilities and system-friendly features, our advanced deflectometry techniques provide powerful options in optical testing. By addressing the challenges in low-order shape measurements and incorporating dark field testing, our approaches extend the potential of deflectometry as a valuable tool in optical metrology across a broad spectrum of industries and scientific endeavors.

Original languageEnglish (US)
Title of host publicationODS 2023
Subtitle of host publicationIndustrial Optical Devices and Systems
EditorsRyuichi Katayama, Yuzuru Takashima
ISBN (Electronic)9781510665828
StatePublished - 2023
EventIndustrial Optical Devices and Systems, ODS 2023 - San Diego, United States
Duration: Aug 21 2023 → …

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceIndustrial Optical Devices and Systems, ODS 2023
Country/TerritoryUnited States
CitySan Diego
Period8/21/23 → …


  • alignment
  • dark field illumination
  • deflectometry
  • optical testing

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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