X光曲面共振腔的共振聚焦效應

Resonant-Focusing Effects for X-rays in Curved Multi-Plate Crystal Cavity

陳松裕(Sung-Yu Chen)

指導教授 ： 張石麟

國立清華大學/理學院/物理學系/博士(2008年)

https://doi.org/10.6843/NTHU.2008.00109

摘要

本論文主要在研究同調性複合式折射透鏡的共振聚焦效應。樣品是利用電離子蝕刻技術在表面方向為(0 0 1)的矽晶圓上製造而成，由多片曲面X光共振腔組成，調整其各項參數而具有複合式折射透鏡的效果。
矽(12 4 0)背向繞射的能量為14.4388 keV，利用超高解析單色光器提高光源解析度，觀察在此能量範圍內(±60 meV)經過同調性複合式折射透鏡的穿透光強度，可看到由空腔共振所造成的干涉條紋。從干涉條紋上選取數個不同能量，利用粗糙度為250Å的刀口橫向切過穿透光在不同位置的積分強度圖形，微分後可得水平光束寬度，藉此求出焦距。
由理論計算中可以看出繞射的聚焦效果會比折射來的大，而實驗上所量得的焦距60 cm，未考慮球面像差下設計的焦距為1m，如果考慮球面像差，折射所造成的焦距為80 cm，實驗值皆比理論值小很多，主要原因來自於曲面的24光背向繞射與X光在裡面的多次來回反射。

關鍵字

聚焦 ； 繞射 ； 曲面共振腔 ； 共振聚焦 ； 複合式折射透鏡

並列摘要

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.

並列關鍵字

focus ； diffraciton ； curevd cavity ； resonant-focusing ； compound refractive lens

參考文獻

10.S. L. Chang, Multiple Diffraction of X-rays in Crystals (SpringerVerlag, Berlin,2004).

12.Y. P. Stetsko and S.-L. Chang, Acta Cryst. A 53, 28 (1997).

13.Andre Authier, Dynamical Theory of X-ray Diffraction(Oxford University Press, 2001).

15.J. M. Vaughan, The Fabry-Perot Interferometer (Hilger Press, Bristol, 1989).

18.Jens Als-Nielsen, Des McMorrow Elements of Modern X-Ray Physics.