연 엑스선을 이용한 고해상도 디지털 인라인 홀로그래픽 현미경

Abstract

Digital in-line holographic X-ray imaging method is invaluable tool to study biological, chemical, physical, and materials science due to ability to image of complex-valued samples without optics, where the resolution limit depends on the illumination wavelength and the numerical aperture of the system. In this thesis, we presents a high resolution digital in-line holographic microscopy by use of highly divergent and coherent soft X-rays. Experiment was performed with a modified full-field transmission lens-based soft X-ray microscope that was newly developed at the Pohang Light Source. The microscope is portable and its sample position is outside the vacuum, which provides easy sample change and in-situ experimental capability. The essential idea of this work is using a spatial filter composed of a Fresnel zone plate and pinhole. The pinhole of 200 nm radius generates highly divergent and highly coherent lights when incidence incoherent lights are tightly focused by the Fresnel zone plate on the pinhole. This combination results in a relatively high numerical aperture reference wave, even with a short wavelength of 2.38 nm. A carbon powder particle, silica powders, spores of penicillium and a lithographic pattern were imaged with a spatial resolution of ~200 nm. This is the highest resolution ever reported with digital in-line holographic microscopy. It approached the theoretically achievable resolution (i.e., the pinhole’s radius) of typical pinhole-based in-line holographic microscopy. It is better than the previously reported best result by a factor of 2.