ABSTRACT In this work, we demonstrate the integration of a flat liquid jet sample delivery system into a compact soft x‐ray absorption spectrometer using a table‐top laser‐induced plasma source. A high‐speed flat liquid sheet is formed by the collision of two cylindrical jets. This micrometer‐thin lamella can ideally be utilized for transmission‐mode soft x‐ray absorption spectroscopy using krypton plasma emission. Detailed analysis of the jet's thickness profile is achieved applying Lambert–Beer's law. Measurements on water, focusing on the oxygen K‐edge, reveal a lamella thickness profile ranging from 500 nm to 1 μm over a length of 3.8 mm. Additionally, we have investigated aqueous solutions of iron salts, capturing near edge x‐ray absorption fine structure spectra over a broad spectral range from the nitrogen K‐edge to the iron L‐edge. Focused analysis on iron species in aqueous solutions enabled us to distinguish quantitatively between the oxidation states of Fe 2+ and Fe 3+ at the iron L‐edge. Our results are compared with measurements obtained under similar conditions at a synchrotron.

The uniformity of a PVD coating process is investigated and adjusted in this work. With the help of a digital twin derived from physical modelling of the plasma and gas flow dynamics in the reactor, it is possible to precisely predict and define the gradients on the individual surface geometries. By using calculated masks, the distribution can be actively influenced. In addition, the predicted distribution during coating can be verified using in-situ characterization techniques using a hyperspectral camera. In this method, the sample is measured using lens optics with a line focus. This measuring system has been implemented in industrial coating systems. The tools presented here expand the portfolio for PVD coating processes. It enables precise layer thickness distributions of uniform and gradient coatings on 2D and 3D substrates.

Extreme ultraviolet (EUV) photon beam characterization techniques, Hartmann wavefront sensing and single shot ablation imprinting, were compared along the caustic of a tightly focused free-electron laser (FEL) beam at beamline FL24 of FLASH2, the Free-electron LASer in Hamburg at DESY. The transverse coherence of the EUV FEL was determined by a Young's double pinhole experiment and used in a back-propagation algorithm which includes partial coherence to calculate the beam intensity profiles along the caustic from the wavefront measurements. A very good agreement of the profile structure and size is observed for different wavelengths between the back-propagated profiles, an indirect technique, and ablation imprints. As a result, the Hartmann wavefront sensor including its software MrBeam is a very useful, single shot pulse resolved and fast tool for non-invasive determination of focal spot size and shape and also for beam profiles along the caustic.

The Small Quantum Systems instrument is one of the six operating instruments of the European XFEL, dedicated to the atomic, molecular and cluster physics communities. The instrument started its user operation at the end of 2018 after a commissioning phase. The design and characterization of the beam transport system are described here. The X-ray optical components of the beamline are detailed, and the beamline performances, transmission and focusing capabilities are reported. It is shown that the X-ray beam can be effectively focused as predicted by ray-tracing simulations. The impact of non-ideal X-ray source conditions on the focusing performances is discussed.

Unraveling the exact nature of nonequilibrium and correlated interactions is paramount for continued progress in many areas of condensed matter science. Such insight is a prerequisite to develop an engineered approach for smart materials with targeted properties designed to address standing needs such as efficient light harvesting, energy storage, or information processing. For this goal, it is critical to unravel the dynamics of the energy conversion processes between carriers in the earliest time scales of the excitation dynamics. We discuss the implementation and benefits of attosecond soft x-ray core-level spectroscopy up to photon energies of 600 eV for measurements in solid-state systems. In particular, we examine how the pairing between coherent spectral coverage and temporal resolution provides a powerful new insight into the quantum dynamic interactions that determine the macroscopic electronic and optical response. We highlight the different building blocks of the methodology and point out the important aspects for its application from condensed matter studies to materials as thin as 25 nm. Furthermore, we discuss the technological developments in the field of tabletop attosecond soft x-ray sources with time-resolved measurements at the near and extended edge simultaneously and investigate the exciting prospective of extending such technique to the study of 2-dimensional materials.

A table-top near-edge X-ray absorption fine structure (NEXAFS) spectroscopy system consisting of a soft X-ray source and an integrated spectrometer with a significantly improved resolution is presented. The soft X-ray source is based on a long-term stable and nearly debris-free picosecond laser-induced plasma generated in a pulsed krypton gas jet target. Photon energies ranging from 250 to 1000 eV can be used for the absorption spectroscopy of thin samples. The newly designed spectrometer accomplishes a spectral resolution of E/ΔE = 1535 at 430 eV, being close to typical synchrotron setups. Moreover, a simultaneous multi-edge analysis is possible. The performance of the new system is demonstrated by investigating the fine structure of the K- and L-absorption edges of various elements (carbon, calcium, oxygen, iron, nickel, and copper) for different types of samples. An excellent agreement with synchrotron spectra is achieved.

We present a new nozzle design for an improved brilliance of laser-produced gas plasmas emitting in the soft X-ray and extreme ultraviolet spectral regime. A rotationally asymmetric gas jet is formed by employing two closely adjacent nozzles facing each other under the angle of 45°. The generated three-dimensional gas density distribution is tomographically analyzed using a Hartmann-Shack wavefront sensor. A comparison with numerical simulations accomplishes an optimization of the nozzle arrangement. The colliding gas jets create an optimized gas distribution with increased density, leading to a significant brilliance enhancement of the extreme ultraviolet, soft X-ray plasma.

In this contribution we present a measuring system, which combines a phase-measuring interferometer with a Hartmann-Shack wavefront sensor. Both systems use the same optical path and microscope objective but they differ fundamentally in their working principle and their metrological properties. The wavefront sensor detects low spatial frequency components of a three dimensional surface with a small number of sampling points based on a single monochrome camera image. The interferometer requires two RGB images to reconstruct the same surface but it detects high spatial frequency surface components, which allow surface roughness measurements. A specific double pulse illumination in combination with a periodic phase modulation is used to obtain the required interferograms in approx. 50 mu s. The combination of the measurement results from the wavefront sensor and the interferometer enables to renounce the use of error-prone phase unwrapping algorithms, to increase the robustness and possible applications. The use of both sensors also increases the robustness and the flexibility compared to a single measurement system. The short data acquisition time enables measurement of moving objects and the application in industrial environments. Various measurement results demonstrate the potential and the limits of this combination of sensors.

Soft X-ray microscopy and absorption spectroscopy are extremely useful tools for high-resolution imaging and chemical analysis of samples in various scientific fields. However, due to the required high photon flux of soft X-ray radiation, up to now, both methods are almost exclusively performed at synchrotron sources. Thus, great efforts have been made to develop table-top sources emitting in the soft X-ray spectral range (lambda = 1-5 nm). Here, the development of a laser-produced plasma source from a pulsed gas jet is presented, enabling the construction of an almost debris-free, compact and long-term stable X-ray source. Based on this source a compact soft X-ray microscope (spatial resolution 50 nm) operating at a wavelength of lambda = 2.88 nm was built and applied for imaging of various test and biological objects. In addition, a laboratory-scale NEXAFS spectrometer has been established, allowing for reliable analysis of different absorption edges at photon energies between 250 and 1250 eV.

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.

Zusammenfassung In diesem Beitrag wird ein Messsystem vorgestellt, das aus der Kombination eines phasenmessenden Interferometers mit einem Hartmann-Shack-Wellenfrontsensor besteht. Die beiden Sensoren nutzen einen gemeinsamen optischen Strahlengang einschließlich eines Mikroskobjektivs, das auf die zu messende Oberfläche gerichtet ist. Sie unterscheiden sich jedoch grundlegend in ihrer physikalischen Funktionsweise und ihren messtechnischen Eigenschaften. Der Wellenfrontsensor erfasst niederfrequente Ortsfrequenzanteile einer dreidimensionalen Oberflächentopographie mit einer vergleichsweise geringen Anzahl an Stützstellen anhand eines einzelnen monochromen Kamerabildes. Das Interferometer benötigt zwei RGB-Aufnahmen zur Rekonstruktion der Phasenkarte derselben Oberflächentopographie und erfasst dabei deutlich höhere Ortsfrequenzanteile, welche für die Rauheitsmessung erforderlich sind. Eine spezielle Doppelpuls-Beleuchtung in Verbindung mit einer periodischen Phasenmodulation ermöglicht die Akquisition der erforderlichen Interferogramme in ca. 50 µs. Die Kombination der Messergebnisse von Wellenfrontsensor und Interferometer ermöglicht den Verzicht auf störanfällige Unwrapping-Algorithmen und erhöht die Flexibilität und das Einsatzspektrum der Sensorkombination im Vergleich zu einem Einzelsensor. Die geringe Zeitdauer zur Erfassung der Topographie eines mikroskopischen Messfeldes erlaubt Messungen an bewegten Messobjekten und bildet damit eine wichtige Voraussetzung für den Einsatz des Sensorsystems in Produktionsanlagen. Die Funktionsweise und die praktische Realisierung des Sensors werden vorgestellt. Messergebnisse von verschiedenen Messobjekten zeigen das Potential dieser Sensorkombination und die jeweiligen Einschränkungen der beiden Sensoren auf.

A compact spectrometer for laboratory NEXAFS measurements, allowing quantitative chemical analysis in the soft X-ray spectral range (250–1000 eV).

Two methods improving the brilliance of laser-induced plasmas emitting in the extreme UV (EUV) and soft x-ray (SXR) region were investigated, using three different gases (nitrogen, krypton, and xenon) from a pulsed gas jet. Utilizing a newly designed piezo electric valve, up to almost ten times higher gas pressures were applied, resulting in increased target densities and thus, higher conversion efficiencies of laser energy into EUV and SXR radiation. Secondly, geometrically reducing the angle between incoming laser beam and observed plasma emission minimizes reabsorption of the emitted short wavelength radiation. Combining both methods, the source brilliance is increased by a factor of 5 for nitrogen. Furthermore, a compact EUV focusing system for metrological applications is presented utilizing the optimized plasma source. An energy density of 1 mJ/cm² at λ = 13.5 nm in the focal spot of an ellipsoidal mirror is achieved with xenon as target gas being sufficient for material removal of PMMA samples with an ablation rate of 0.05 nm/pulse.

Two methods improving the brilliance of laser-induced plasmas emitting in the extreme UV (EUV) and soft x-ray (SXR) regions were investigated, using three different gases (nitrogen, krypton, and xenon) from a pulsed gas jet. Utilizing a newly designed piezoelectric valve, up to almost ten times higher gas pressures were applied, resulting in increased target densities and thus, higher conversion efficiencies of laser energy into EUV and SXR radiation. Secondly, geometrically reducing the angle between the incoming laser beam and the observed plasma emission minimizes reabsorption of the emitted short wavelength radiation. Combining both methods, the source brilliance is increased by a factor of 5 for nitrogen. Furthermore, a compact EUV focusing system for metrological applications is presented utilizing the optimized plasma source. An energy density of 1 mJ/cm2 at wavelength λ = 13.5 nm in the focal spot of an ellipsoidal mirror is achieved with xenon as the target gas being sufficient for material removal of PMMA samples with an ablation rate of 0.05 nm/pulse.

In this work the influence of non-uniformity effects on the spectral transmission properties of broad-band dielectric optical coatings was examined. Recently, it was observed that in modern complex dielectric coatings significant spectral, resonantlike errors of the reflected wavefront can occur at specific wavelengths, which are induced by lateral coating nonuniformities [1]. For a detailed investigation of this effect, a setup was developed for monitoring the spectrally dependent wavefront error, utilizing a broad-band monochromatized plasma lamp (spectral range from 400 – 900nm) as light source and a high sensitivity Hartmann-Shack wavefront sensor for detection of reflected or transmitted wavefronts. In addition, a method for absolute and relative calibration of the measured wavefront error is presented. Two broadband dielectric beam splitters (#1 and #2) deposited by magnetron sputtering (high reflectance 400 – 900 nm, high transmittance 920 – 2300 nm) with different coating specifications were analyzed. It could be shown, that for an optimized design the spectral wavefront error can be significantly reduced compared to a standard beam splitter design [2].

Absorption-induced lens heating within optical elements can diminish the achievable resolution of the lithographic process in semiconductor wafer steppers, as the distortion of the transmitted wavefront leads to deteriorations of the imaging performance. In reverse, sensitive monitoring of thermally induced wavefront distortions also establishes a procedure for fast and precise absorption measurements, since the extent of deformation is directly proportional to the absorption loss. In this paper a parallelized photo-thermal absorption measurement system based upon a Hartmann-Shack wavefront sensor with extreme sensitivity is presented, providing quantitative absorptance data of optical materials with sub-ppm resolution. Caused by the temperature dependence of the refractive index as well as thermal expansion, the initially plane wavefront of a probe beam is distorted into a convex or concave lens, depending on sign and magnitude of index change and expansion. Wavefront deformations as low as 50pm (rms) can be registered. Moreover, due to the spatial resolution of the employed wavefront sensor, the technique is insensitive to misalignments, allowing for a rapid and reliable assessment of material quality. Absolute calibration of the absorption data is achieved by comparison with a thermal calculation. The method accomplishes not only to measure absorptances of plane optical elements, but also wavefront deformations and focal shifts in lenses as well as in complex optical systems. Thus, it is employed already at many places in the semiconductor industry for quality assurance of test optics and components. Along with a description of the technique we present results from absorption measurements on coated and uncoated optics as well as mirrors for 193nm and 248nm. Extensions to EUV optics are discussed.

The present paper addresses uniformity effects in demanding dielectric optical coatings. The origins of spectral resonant wavefront errors (WFE) induced by non-uniformities in complex dielectric filters are investigated in detail. The coating is a broad-band beamsplitter with a high reflectance between 400 and 900 nm and a high transmittance between 920 and 2300nm. The WFE can significantly be reduced with an optimized design. A new setup based on Hartmann-Shack sensors measures the spectrally dependent WFE in the visual spectral range. The paper presents a method for referencing the measured data. The experimental WFE maps obtained by spectral Hartmann-Shack measurements agree well with the expected spectra taken from spectral photometric measurements and the coating design. The paper also addresses coatings on curved surfaces. A band pass filter centered at 670 nm on the convex side of a lens was developed. Using a combination of a sub-rotation and special uniformity masks, a very low spectral shift of the passband position overall the lens surface could be demonstrated. The deposition concept and mask design, respectively, are developed via simulation studies based on a simulation approach shown in [10]. Extension of the model framework by plasma simulation and a concept for computing deposition profiles on moving 3D substrates was required for solving the problem.