Imaging with parabolic refractive X-ray lenses (2005)

When Wilhelm C. Roentgen discovered the x-ray radiation in 1895, he made use of its large penetration depth in matter to create projections of different opaque objects, and also of bones inside the body. The imaging of dense matter inside the body has rapidly found wide use in medicine and is nowadays an important diagnostic tool. But imaging with x-ray radiation is also used in research and technology. The development of 3 dimensional imaging by means of tomographic reconstruction in the late 1960's by G. N. Houndsfield has enhanced the possible applications of x-ray radiation. In many areas of research, technology and medicine 3 dimensional imaging techniques have found a wide spread use, especially the x-ray tomography. Without use of an optic the lateral resolution of x-ray images or tomograms is limited by the resolution of state of the art CCD-detectors to about 10 micrometers. Using a scintillator to convert the x-ray image into visible image and magnifying it by means of an optic for visible light gives CCD-images with some micrometers resolution. For more and more areas as, for instance, material science, geophysics, plant physiology, analysis of art objects, and also medical research a higher lateral resolution is needed. Using x-ray optics better resolutions are possible, as typical wavelengths of x-ray radiation are in the Angström and sub-Angström range. The development of x-ray optics has proven to be difficult due to the weak refraction of x-rays in matter. The index of refraction of x-ray radiation in matter is slightly smaller than 1, whereas for visible light in glass it is about n = 1.5 . The refractive index of x-ray radiation is specified in the form n = 1 - delta + i beta, where the decrement delta is of the order of 10^(-6), the absorptive component beta being typically one or two orders of magnitude smaller. After an introduction, an overview of x-ray sources is given in chapter 2 of this thesis. Chapter 3 reviews the most important optical devices used at present for x-ray radiation (monochromators, mirrors and light-guides, multilayers, Fresnel-zone plates, ...). The main focus of this thesis is in the area of the development and manufacturing of refractive x-ray lenses, as well as their applications, i.e. at synchrotron sources of the third generation like the European Synchrotron Radiation Facility (ESRF). Chapter 4 describes in detail the parameters which have to be considered in the process of fabricating parabolic refractive x-ray lenses, especially the choice of the right materials. The optical properties of these lenses and their applications are also discussed there. In chapter 5 imaging by means of parabolic refractive x-ray lenses using coherent and incoherent illumination is described. A device, developed during the work for this thesis, to reduce the coherence of the illumination in a controlled way is presented in this chapter, as well as the x-ray microscopy, the x-ray lithography, and the generation of a micro beam for high resolution analyses by scanning. These applications are demonstrated at some examples and the achieved 2 dimensional resolution of about 100 nanometers is documented. In chapter 6 the mathematical theory of tomographic reconstruction is shown and the magnified x-ray tomography using refractive lenses is presented. The achieved 3 dimensional resolution of 250 nanometers is shown at some examples. The last chapter comprises a summary of this thesis.