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27 September 2008 Active beam control for the EUV/XUV spectral range using an adaptive Kirkpatrick-Baez arrangement
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Triggered by the roadmap of the semiconductor industry, tremendous progress has been achieved in the development of extreme ultraviolet (EUV) sources and high-quality EUV optical coatings in recent years, opening up also new fields of applications apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis. The Laser-Laboratorium Göttingen e.V. has developed a laser-driven plasma source for generation of soft X-rays in the spectral range 2...20 nm. A Nd:YAG laser (1064 nm, 800 mJ, 6 ns) is focused into a gas-target leading to plasma formation which in turn emits characteristic soft X-ray radiation. Depending on the employed target gas, narrow-band as well as broad-band spectra can be obtained. For focusing a Kirkpatrick-Baez optics is used, providing broad-band light steering due to grazing-incidence reflection. The mirrors of the arrangement are formed by bent silicon wafer slices allowing continuous tuning to the desired curvatures. The motorized control offers active adaption of surface shape and incidence angles even in high vacuum, to various experimental demands (e.g. focusing on different sites, beam collimation). For reduction of aberrations the optical system was fine-adjusted with the help of a Hartmann-Shack wavefront sensor in the visible spectral range. The wave propagation properties were determined and compared to calculations performed with ZEMAX. From the difference between calculated phase and measured wavefront direct information about the figure error between perfect and real mirrors could be obtained.
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Armin Bayer, Frank Barkusky, Stefan Döring, Bernhard Flöter, Christian Peth, and Klaus Mann "Active beam control for the EUV/XUV spectral range using an adaptive Kirkpatrick-Baez arrangement", Proc. SPIE 7100, Optical Design and Engineering III, 71001F (27 September 2008);

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