An off-axis differential method for improvement of a femtosecond laser differential chromatic confocal probe

Chong Chen, Yuki Shimizu, Ryo Sato, Hiraku Matsukuma, Wei Gao

Research output: Contribution to journalArticlepeer-review

Abstract

This paper presents an off-axis differential method for the improvement of a femtosecond laser differential chromatic confocal probe having a dual-detector configuration. In the proposed off-axis differential method employing a pair of single-mode fiber detectors, a major modification is made to the conventional differential setup in such a way that the fiber detector in the reference detector is located at the focal plane of a collecting lens but with a certain amount of off-axis detector shift, while the fiber detector in the measurement detector is located on the rear focal plane without the off-axis detector shift; this setup is different from the conventional one where the difference between the two confocal detectors is provided by giving a defocus to one of the fiber detectors. The newly proposed off-axis differential method enables the differential chromatic confocal setup to obtain the normalized chromatic confocal output with a better signal-to-noise ratio and approaches a Z-directional measurement range of approximately 46 µm, as well as a measurement resolution of 20 nm, while simplifying the optical alignments in the differential chromatic confocal setup, as well as the signal processing through eliminating the complicated arithmetic operations in the determination of the peak wavelength. Numerical calculations based on a theoretical equation and experiments are carried out to verify the feasibility of the proposed off-axis differential method for the differential chromatic confocal probe with a mode-locked femtosecond laser source.

Original languageEnglish
Article number7235
Pages (from-to)1-15
Number of pages15
JournalApplied Sciences (Switzerland)
Volume10
Issue number20
DOIs
Publication statusPublished - 2020 Oct 2

Keywords

  • Chromatic confocal probe
  • Femtosecond laser
  • Off-axis differential method
  • Tracking local minimum method

ASJC Scopus subject areas

  • Materials Science(all)
  • Instrumentation
  • Engineering(all)
  • Process Chemistry and Technology
  • Computer Science Applications
  • Fluid Flow and Transfer Processes

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