A displacement probe using backscattering for profiling the ground surface form

In Ung Song, Ho Soon Yang, Jun Gyu Park, Goeun Kim, Kyuman Cho, Sug Whan Kim

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


We present a new displacement probe for a gantry-type profilometer to measure the ground surface form. The system is based on heterodyne interferometry with an acousto-optic modulator (AOM) and I/Q demodulation scheme. When the light from the single-frequency laser diode passes through the AOM following the Bragg condition angle, it is divided into the non-diffracted zero-order and a diffracted first-order beam with a frequency shift as the amount of the AOM driving frequency. One beam is used for the test and the other for the reference beam. Orthogonally reflected beams pass through the AOM one more time, and these beams make a heterodyne signal with a double modulation frequency. In this case, the only backscattered beam from the ground surface satisfies the Bragg condition, producing the modulated interference. Therefore, the AOM tends to reduce the stray light noises from the other incidence angles, acting as a transmission filter for backscattered light. The interference light arrives at the high-speed photodiode and it is then demodulated using the I/Q demodulation to extract the phase value. Although the backscattered ray from the rough glass surface has a very low intensity, the I/Q interferometer can detect the signal because the phase can be acquired regardless of the intensity change. Preliminary experiments confirmed that the system can measure from backscattered light of ground glass surface form.

Original languageEnglish
Title of host publicationApplied Optical Metrology IV
EditorsErik Novak, James D. Trolinger, Christopher C. Wilcox
ISBN (Electronic)9781510644724
Publication statusPublished - 2021
EventApplied Optical Metrology IV 2021 - San Diego, United States
Duration: 2021 Aug 12021 Aug 5

Publication series

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


ConferenceApplied Optical Metrology IV 2021
Country/TerritoryUnited States
CitySan Diego

Bibliographical note

Publisher Copyright:
© 2021 SPIE.

All Science Journal Classification (ASJC) codes

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


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