Study on Three-Dimensional Imaging and Surface Profiling Based on Digital Holographic Microscopy and Structured Illumination Microscopy

Abstract

Imaging technology is widely used throughout industry, research, and everyday life. The demands of these imaging technologies are being extended from existing 2D to 3D. As the technology of imaging is changing from 2D to 3D, there are additional problems that arise. The first is the depth of field problem. Most imaging optics require high resolution and the need for high resolution reduces the depth of field. In addition, sample images that are out of the depth of field will be imaged blurred. A narrow range of depth of field is not an issue with 2D imaging, but 3D imaging is a disadvantage when imaging the entire volume of a sample. The second is a scanning problem. Fast, accurate scanning of the focal plane is essential for 3D imaging. In addition, it is required to solve vibration and magnification change problems that can be caused by scanning. In this thesis, Digital holographic microscopy (DHM) and Structured illumination microscopy (SIM) have been implemented to solve the problems of 3D imaging. DHM is a novelty optical method that can reconstruct a three-dimensional image through a numerical propagation with a single hologram. It is important to select the propagation distance in order to reconstruction image of the desired position in DHM. It can be automated by evaluating the contrast of the reconstructed image and this is called auto-focus method. DHM's autofocus method can be applied to correct three-dimensional images outside of the depth of field, and this is implemented by correcting the vessel image of optical coherence tomography (OCT). We also investigated how to apply electrically tunable lens (ETL) to imaging optics for fast scanning of 3D imaging. Moving a sample to perform scanning of a three-dimensional image can be accompanied by motion that is slow and can cause vibration, which can degrade the image quality. In order to solve this problem, there have been studied methods of fixing the sample and moving the focal plane of the optical system to perform three-dimensional scanning. As one of them, we implemented a method to apply ETL. The ETL is a device that can change the focal length of the lens according to the applied current. It has the advantage of fast and accurate change of focal length. The ETL is applied to 4f relay optical system to realize a magnification-invariant scanning system with long focus variable distance and little variation of magnification. The magnification- invariant scanning system has been implemented in structured illumination microscopy to measure the surface of a three-dimensional object. It was also implemented by applying a scanning system using DHM and ETL to track the sample in order to follow the drifting sample. Through this research, we have implemented a solution to the problem of drafting, image defocusing, and scanning, which are caused by the depth of field. The problem of drafting the sample was solved by the autofocus tracking system with DHM and ETL scanning system. The image defocusing problem was solved by correcting the image using DHM and auto focus method. Scanning with difficulty in changing of magnification and vibration is solved with the fast 4f relay system using ETL.