The objective of this research was to develop a three-dimensional (3D) reconstruction system based on a time-domain optical coherence tomography (OCT) microscope. One of the critical drawbacks of OCT microscopes is that their axial measurement ranges are typically limited by their depths of field (DOFs), which are determined by the numerical apertures of their objective lenses and the central wavelengths of their light sources. If a low-coherence interference fringe is far outside the DOF, the measurement accuracy inevitably decreases, regardless of how well-adjusted the reference mirror is. To address this issue and improve the axial measurement range of the OCT microscope in this study, an object-scanning measurement scheme involving a Linnik interferometer was developed. To calibrate the system in the proposed technique, image post-processing is performed for a well-conditioned state to ensure that a low-coherence interference fringe is generated within the DOF, enabling 3D objects with high-aspect-ratio structures to be scanned along the axial direction. During object-scanning, this state is always monitored and is corrected by adjusting the reference mirror. By using this method, the axial measurement range can be improved up to the working distance (WD) of the objective lens without compromising the measurement accuracy. The WD is typically longer than 10 mm, while the DOF of the microscope is around 0.01 mm in general, although it varies depending on the imaging system. In this report, the experimental setup of a 3D reconstruction system is presented, a series of experimental verifications is described, and the results are discussed. The axial measurement range was improved to at least 35 times that of a typical OCT microscope with identical imaging optics.

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