The first part of this chapter comprises setups and results of the determination of wavefront and beam parameters for different EUV sources (free-electron lasers, HHG-sources, synchrotron radiation) by self supporting Hartmann-Sensors. We present here i.a. a sensor applied for alignment of the ellipsodial mirror at FLASH beamline 2, yielding a reduction of the rms-wavefront aberrations by more than a factor of 3. In the second part we report on the characterization of the Free-Electron-Laser FLASH at DESY by a quantitative determination of the Wigner distribution function. The setup, comprising an ellipsodial mirror and a moveable extreme UV sensitive CCD detector, enables the mapping of two-dimensional phase space corresponding to the horizontal and vertical coordinate axes, respectively. Furthermore, an extended setup utilizing a torodial mirror for complete 4D-Wigner reconstruction has been accomplished and tested using radiation from a multimode Nd:VO4 laser.

We report on online measurements of photon beam parameters during mirror alignment in the soft x-ray spectral region of FLASH, the free-electron laser in Hamburg. A compact Hartmann sensor operating in the wavelength range from 6 to 35nm was used to determine the wavefront quality of individual free-electron laser (FEL) pulses during the alignment procedure as well as aberrations. Beam characterization and alignment of beamline BL3 was performed with lambda(13.5nm)/116 accuracy for wavefront rms (W-rms). Second moment beam parameters are computed using a spherical reference wavefront generated by a 5 mu m pinhole. The Hartmann sensor was used for alignment of the ellipsoidal focusing mirror of beamline BL3, resulting in a reduction of W-rms by 33%.

In den letzten Jahren haben mehrere Freie-Elektronen-Laser (FEL) im Röntgen-Spektralbereich den Nutzerbetrieb aufgenommen. Sie erzeugen 10-100 Femtosekunden lange Pulse mit hohem transversalen Kohärenzgrad und schmalbandigem Frequenzspektrum und erreichen gegenüber einfacher Undulatorstrahlung eine etwa zehn Größenordnungen höhere Spitzenbrillanz. Ein Hartmann-Wellenfrontsensor wurde für den EUV- und weichen Röntgen-Spektralbereich entwickelt, der bezogen auf die Wellenfrontrauigkeit wrms im Einzelpuls bei der Wellenlänge λ=13nm die Wiederholgenauigkeit λ/116 erreicht und an den Freie-Elektronen- Lasern FLASH in Hamburg und LCLS in Stanford zur Wellenfrontmessung und Strahlcharakterisierung eingesetzt wurde. Es wurden typische, durch den SASE- Erzeugungsprozess der Strahlung bedingte Schwankungen des Strahldurchmessers, der Strahllage und der Intensität festgestellt. Die Strahlqualität der einzelnen Pulse ist hoch mit Beugungsmaßzahl nahe eins. Durch Kontrolle und Justage der optischen Elemente, insbesondere der fokussierenden Spiegel, wurden die Strahleigenschaften an den Beamlines optimiert. Vergleichende Strahlprofilmessungen mittels einer EUV-Kamera um die Strahltaille bestätigen die aus der Hartmann-Messung gewonnenen Strahlparameter. Eine Rekonstruktion der Wignerfunktion des Strahls liefert zusätzliche Informationen über den Kohärenzgrad.

We report on online measurements of beam parameters in the soft X-ray and extreme ultraviolet (EUV) spectral range at the free-electron laser FLASH. A compact, self-supporting Hartmann sensor operating in the wavelength range from 6 to 30 nm was used to determine the wavefront quality of individual free-electron laser (FEL) pulses. Beam characterization and alignment of beamline BL1 was performed with λ13.5 nm/90 accuracy for wavefront rms (wrms). A spot size of 159 μm (second moment) and other beam parameters are computed using a spherical reference wavefront generated by a 5 μm pinhole. Beam parameters are also computed relative to a reference wavefront created by a laser-driven plasma source of low coherence, proving the feasibility of such a calibration and reaching λ13.5 nm/7.5 wrms accuracy. The sensor was used for alignment of the toroidal focusing mirror of beamline BL1, resulting in a reduction of wrms by 25%, and to investigate wavefront distortions induced by thin solid filters.

The Free-Electron-Laser FLASH at DESY has been characterized by a quantitative determination of the Wigner distribution function. The setup, comprising an ellipsodial mirror and a moveable extreme UV sensitive CCD detector, enables the mapping of two-dimensional phase spaces corresponding to the horizontal and vertical coordinate axes, respectively. For separable beams this yields the entire Wigner distribution, offering comprehensive information about spatial coherence properties, wavefront, beam profiles, as well as beam propagation parameters.

A compact, self-supporting Hartmann wavefront sensor was developed for the extreme ultraviolet (EUV) and soft x-ray range. The device is adapted to the characteristics of the Free-electron LASer in Hamburg (FLASH). It operates in a wavelength range from 6 to 30 nm with the capability to measure the wavefront quality of individual free-electron laser (FEL) pulses for beam characterization as well as for beamline alignment and monitoring behind user experiments. We report on online-Hartmann wavefront measurements at beamline BL2 with lambda(13.5) nm/90 accuracy for wavefront rms (w(rms)). The results were used to align the ellipsoidal focusing mirror at the beamline, decreasing the residual root mean square (rms) wavefront aberrations by more than a factor of 3 to 2.6 nm. The spot size of 31 mu m (x) and 27 mu m (y) full-width at half-maximum (FWHM) as well as other beam parameters evaluated from wavefront and intensity data are consistent with independent profile measurements in the focal region, employing both a high-resolution EUV camera and poly(methyl metacrylate) (PMMA) imprints.

In recent years, technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. Currently, the application of EUV radiation apart from microlithography comes more and more into focus. Main goal of our research is to utilize the unique interaction between soft x-ray radiation and matter for probing, modifying, and structuring solid surfaces. In this contribution we present a setup capable of generating and focusing EUV radiation. It consists of a table-top laser-produced plasma source. In order to obtain a small focal spot resulting in high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to this source, simultaneously blocking unwanted out-of-band radiation. By demagnified (10x) imaging of the plasma an EUV spot of 5 μm diameter with a maximum energy density of ~7.4 J/cm² is generated (pulse length 8.8 ns). We present first applications of this integrated source and optics system, demonstrating its potential for high-resolution modification and structuring of solid surfaces. As an example, etch rates for PMMA, PC and PTFE depending on EUV fluences were determined, indicating a linear etch behavior for lower energy densities. In order to investigate damage tests on EUV sensors and optics, 1-on-1 damage tests were performed on grazing incidence gold mirrors, Mo/Si multilayer mirrors and mirror substrates. To our knowledge, this is the first time that such experiments using nanosecond EUV-pulses were carried out.

In recent years, technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. So far, intense light sources based on discharge or laser plasmas, beam steering and imaging optics as well as sensitive detectors are available. Currently, applications of EUV radiation apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis come more and more into focus. In this contribution we present an overview on the EUV/XUV activities of the Laser-Laboratorium Göttingen based on table-top laser-produced plasma (LPP) sources. As target materials gaseous or liquid jets of noble gases or solid Gold are employed. Depending on the applications, the very clean but low intense gaseous targets are mainly used for metrology, whereas the targets for high brilliances (liquid, solid) are used for microscopy and direct structuring. For the determination of interaction mechanisms between EUV radiation and matter, currently the solid Gold target is used. In order to obtain a small focal spot resulting in high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to this source. By demagnified (10x) imaging of the Au plasma an EUV spot of 3 μm diameter with a maximum energy density of ~1.3 J/cm2 is generated (pulse duration 8.8 ns). First applications of this integrated source and optics system reveal its potential for high-resolution modification and direct structuring of solid surfaces. For chemical analysis of various samples a NEXAFS setup was developed. It consists of a LPP, using gaseous Krypton as a broadband emitter in the water-window range, as well as a flat field spectrograph. The laboratory system is set to the XUV spectral range around the carbon K-edge (4.4 nm). The table-top setup allows measurements with spectral accuracy comparable to synchrotron experiments. NEXAFS-experiments in transmission and reflection are demonstrated. Beside chemical investigations, also microscopy applications are performed within the XUV spectral range. For this reason a water-window microscope was developed, based on a liquid argon LPP target. The XUV radiation is focused by a Cr/Sc multilayer mirror, leading to spectral narrow band radiation on the sample. For magnifying the sample, a Fresnel zone plate will be used with an outer zone width of 50 nm. Additionally to these applications, an EUV/XUV setup for structural analysis was developed. Using a spectral broad band emitting Xenon gaseous target combined with a grazing incidence optics (Kirkpatrick-Baez arrangement), it offers the possibility to perform angular resolved reflectivity-, diffraction- and scattering experiments as well as NEXAFS analysis in one setup. In completion to these experiments with LPP sources, an EUV/XUV Hartmann-type wavefront sensor has been developed in collaboration with DESY HASYLAB. It consists of a pinhole array, positioned in front of a XUV sensitive CCD camera with quantum converter. With custom-developed software the incident wavefront can be determined. This sensor is currently used at the free electron laser FLASH in Hamburg for beam characterization.

This paper presents the development of a laser-driven plasma source for soft X-ray production in the 2-20 nm spectral range. In the experiment, a Nd:YAG laser (1064 nm, 800 mJ, 6 ns) is focused into a gas-target, that leads to the formation of a plasma, which in turn emits characteristic soft X-ray radiation. A flexible Kirkpatrick-Baez optics is developed for focusing, which provides broadband light steering due to grazing incidence reflection. The carbon-coated mirrors of this device are formed by bent silicon wafer slices, that allow continuous tuning to the desired curvatures. Structural and chemical surface analysis are shown by utilizing the described system. Results on near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the carbon K-edge are also presented. Hence, NEXAFS spectroscopy using a table-top XUV source can be considered as a highly surface sensitive fingerprint method for chemical analysis.

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 Gottingen 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.