3-D Image reconstruction based on optical interferometry

Abstract

Optical coherence tomography (OCT), based on a vertical scanning Michelson interferometer with a superluminescent diode (SLD), was applied for constructing a surface profile of material. To reduce time-consuming process, a parallel light beam and a CCD camera were set in this OCT. In this technique, each pixel of CCD camera acted as a separated light detector. Interferogram, taken by each pixel of CCD camera, was finally analyzed by two signal analysis methods. For comparing the efficiencies of two signal analysis methods, a continuous wavelet transform (CWT) and a discrete Fourier transform (DFT), surface profiles of a step-height standard plate were first individually determined by these two kinds of signal analysis methods. The result showed that the surface profile, constructed by CWT, was more closed to a real sample surface than the one constructed by DFT. Next, surface cross-sections of three stainless steel plates (Sample No.1, No.2 and No.3) were also defined by analyzing their interferograms with both CWT and DFT. For Sample No.1 and No.2, root-mean-square roughness (Rq) of cross-section, analyzed by CWT, was acceptable by comparing with the one, measured by SP-500 Series of Toray, used as a standard tool. But the uncertainty ranges of Rq for Sample No.3, analyzed with both methods, did not overlap with the ones measured by our standard tool. It was caused by the difference in analysis method and more surface roughness of this Sample No.3. Next, OCT with CWT was applied to construct surface profiles of these three samples, while their surfaces were covered with a cover slide. By comparing the profiles of covered surfaces with the uncovered ones, consistencies of their surface profiles were existed. Finally, this OCT was applied for measuring thickness of a cover slide. It was found that its thickness, measured by our OCT, was significantly closed to the one measured by ULM RUBIN 800 of MAHR.