數位全像顯微術及斷層造影之研究

Abstract

數位全像基於全像干涉之原理，可從所記錄之數位全像片中量化分析光波中之數位振幅資訊，並已被廣泛應用於測量經過樣品之光波資訊。而在本論文中，我們提出數種技術應用於數位全像顯微術中，並用以測量諸如折射率等之樣品的光學資訊。首先，我們提出應用數位全像顯微術來進行全像記錄之即時現場量測，借以獲得在全像記錄材料於記錄過程中，光致折射率條紋之動態變化，此為第一次同時記錄全像片並同步觀測其折射率變化之研究，相較於直接以光學讀取全像片內容，本研究所提供的數位全像顯微造影之方法可更直觀且微觀全像片記錄過程之記錄機制。接著為了可直接取得穿透或半穿透材料之折射率變化，而不受限於所取得相位所代表的累計光程差，我們率先提出了一嶄新的穿反式數位全像顯微術之架構，此方法可用以同時取得微光學元件之穿透與反射的光場，並分別藉由其重建出的相位資訊以分析其中所包含的折射率變化，相對於傳統之折射率測量之技術，本研究可避免複雜的掃描機制，而可達非接觸與快速測量樣品之整面的空間折射率變化。然而，上述所提出的技術依然無法完全解決相位中所包含的累計光程差的限制，因此所取得的結果無法描述實際物體的內部三維分布資訊。因此，本論文也提出兩種不同之斷層影像的技術。首先是低同調數位全像顯微術，透過低同調光源的同調選波之原理，可用以測量物體內部不同深度的整面之切片影像，此方法首先達到以低同調光源下之相移式數位全像顯微術，來進行活體生物樣品之切片斷層掃描之研究。然而因部份樣品其較低的反射光強度，因此低同調的顯微架構難以應用於穿透式樣品，為取得穿透式樣品內部的完整折射率資訊，我們提出了一新穎的同軸旋轉式數位全像顯微斷層系統，此技術率先參考於傳統的電腦斷層之掃描方式，將其融入數位全像顯微斷層之技術中，其入射光源與量測系統將以樣品為圓心進行旋轉。而透過此種光學繞射斷層掃瞄的技術，我們可以數位全像顯微術取得不同角度之穿透光場，並以傅氏繞射理論計算與分析樣品內部的三維折射率分布。也正因此，本研究所提出的同軸旋轉之架構，可領先於其他斷層技術，進行樣品於液體環境下之顯微斷層的量測，而不會影響樣品之穩定性，且其重建之模型依然可使用對稱性較好的樣品旋轉之模式進行斷層影像之重建。最後，本研究亦首先提出一環場光束旋轉之數位全像顯微斷層之設計概念，此法可做為未來改善同軸旋轉系統架構下，複雜且耗時之旋轉系統的機制。以上研究相關的實驗與結果，將於接下來的本文當中詳細的描述與探討。Digital holography has been widely investigated and has great potential for applications such as measuring whole wavefronts of a sample because it can quantitatively assess all information in a complex wavefront derived from a digital hologram. And in this study we proposed the several digital holographic microscope techniques to measure the optics properties, such as refractive index for the samples. Firstly, we present a technique for in situ measurement of light-induced refractive index gratings in epoxy resin using digital holographic microscopy. Grating formation and dynamic behavior of the recording medium during the light-induced holographic process was first time to be demonstrated experimentally and characterized using the proposed scheme. Compared with an optical holographic readout, the proposed technique facilitates direct observation and substantial understanding of the holographic recording mechanism in a microscopic view. Then, in order to directly measure the spatial distribution of the refractive index of transparent or semi-transparent micro-optical elements, we propose the transflective digital holographic microscope system, which can simultaneously record both the transmitted and the reflected waves from micro-optical element and then numerically reconstructs the phase information and refractive index profile. Unlike the conventional scanning refractive ray method, the proposed method supports the rapid full-field nondestructive measurement and direct observation of the spatial index variation and structure of micro-optical elements. However above method can only measure the integral phase information through the sample but not obtain the distribution inside the sample. So this study also proposed a low coherence digital holographic microscope which demonstrates an en face sectional imaging at the different depth inside the sample. This is the first time where a low coherence phase-shifting holographic microscope has been applied to the sectional imaging of a biological specimen under an in vivo environment. Finally, in order to obtain more complete information inside the transparent sample, we proposed a novel optical section imaging technique to measure the spatially refractive index (RI) distribution inside the sample by digital holographic microtomography system. In this tomographic study we use coaxial rotation architecture, whose illuminated laser source and image sensor are lined up and simultaneously rotated around the sample. This architecture was the first one to measure the sample immersed in the liquid medium based on the sample rotation formula, which would not disturb the sample when rotate the whole imaging system during the tomographic recording process. As the computerized tomography, the 3D refractive index distribution inside the sample can be calculated with different transmitted wavefronts according to the Fourier diffraction theorem. Also we proposed an omnidirectional synthetic aperture digital holographic microtomography system to induce the complex rotation mechanism in the coaxial rotation architecture. The experiments and results of the above study works are presented and discussed.