| Summary: | 博士 === 國立清華大學 === 物理學系 === 97 === The thesis reports on the coherent-focusing effects for X-rays in curved multi-plate crystal cavities. These multi-plate crystal devices, consisting of compound refractive lenses, were prepared on silicon (0 0 1) wafers by lithographic techniques. Each lens acts also as a mirror to reflect the incident X-rays back and forth inside the cavities via the (12 4 0) back diffraction. In principle, this kind of crystal devices may produce well-focused coherent beams, provided the required experimental conditions are properly fulfilled.
In this study, X-ray (12 4 0) back diffraction at the photon energy of 14.4388 keV from these monolithic silicon crystal devices showed interference fringes due to cavity resonance through the compound refractive lenses (CRL). Under this condition, we measured the transmitted integrated intensity profile by using a knife-edge scanning across the transmitted beam and analyzed its beam size. The focusing effect and its mechanism could then be deduced.
From the theoretical calculations, we know that the focusing effect from diffraction is stronger than from refraction. The experimental results show that the focal length is about 60 cm, compared to the designed value, 1 m., for the CRL. If we consider the spherical aberration, the theoretical focal length is reduced to 80 cm., that is still larger than the measured value. This difference is due mainly to the dynamical diffraction effects of the transmitted and reflected beams traveling back and forth in between the crystal-plates of curved surface. In addition, the 24-beam diffraction may affect the focusing as well.
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