High-Dynamic-Range, High-Precision, High-Speed Surface Profile Measurement Using Swept Source Optical Coherence Tomography

The measurement of a 3-D surface profile is essential for evaluating product quality, gaining importance with advances in manufacturing technology. Swept-source optical coherence tomography (SSOCT) offers the advantages of high speed and high measurable range (or dynamic range) and has become a powerful tool in biomedical imaging. However, the axial resolution of SSOCT (~a few micrometers) is relatively low for high-precision surface profile measurement. The improvement of axial resolution is constrained by the spectrum sweep repeatability. In this study, we present a new SSOCT-based method to calculate the optical path difference (OPD) between the sample surface and the reference arm. The method only uses a segment of the interference spectrum for OPD calculation and thus reduces the effective data volume. The axial resolution was improved to submicrometer without sacrificing the dynamic range. Surface profile measurements were performed on step gauges and coins. The results demonstrated that equipped with the proposed method SSOCT has the potential to be a useful tool for high-speed, high-dynamic range, and high-precision surface profile measurement.