Abstract:

The renaissance of Extreme Ultraviolet (EUV) and soft x-ray (SXR) optics in recent years is mainly driven by the desire of printing and observing ever smaller features, as in lithography and microscopy. This attribute is complemented by the unique opportunity for element specific identification presented by the large number of atomic resonances, essentially for all materials in this range of photon energies. Together, these have driven the need for new short-wavelength radiation sources (e.g. third generation synchrotron radiation facilities), and novel optical components, that in turn permit new research in areas that have not yet been fully explored. This dissertation is directed towards advancing this new field by contributing to the characterization of spatial coherence properties of undulator radiation and, for the first time, introducing Fourier optical elements to this short-wavelength spectral region.

The first experiment in this dissertation uses the Thompson-Wolf two-pinhole method to characterize the spatial coherence properties of the undulator radiation at Beamline 12 of the Advanced Light Source. High spatial coherence EUV radiation is demonstrated with appropriate spatial filtering. The effects of small vertical source size and beamline apertures are observed. The difference in the measured horizontal and vertical coherence profile evokes further theoretical studies on coherence propagation of an EUV undulator beamline. A numerical simulation based on the Huygens-Fresnel principle is performed.

Accurate knowledge of the refractive index in this wavelength region is of fundamental importance for the design of optical systems. However, due to the high absorption, no previous direct measurement of the real part of the refractive index has been performed at EUV wavelengths. To overcome these limitations, a novel diffractive optical element based on Fourier optics techniques is invented, fabricated, and demonstrated for the first time. The improved efficiency of the interferometer employing this novel optical element enables the first direct measurement of the refractive index at EUV wavelengths. Both the real and imaginary parts of the complex refractive indices are measured directly, without recourse to Kramers-Kronig transformations. Data for Al and Ni, in the vicinity of their L and M-edges, respectively, are presented as first examples of this technique.

The first novel Fourier optical element used in the above EUV interferometer is also discussed in detail. This diffractive optical element, when illuminated by a uniform plane wave, will produce two symmetric off-axis first order foci suitable for interferometric experiments. In addition to the symmetricalness, the flux throughput is improved by ~10 times as compared with separate elements providing the same functionality. The efficiency of this optical element is measured. Future work on computer generated holograms is suggested and compared with the Fourier optical element. The invention of this Fourier optical element opens a new era in the use of sophisticated optical techniques at short wavelengths.