This PDF file contains the front matter associated with SPIE Proceedings Volume 8678, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Next-generation X-ray sources, based on the X-ray Free Electron Laser (XFEL) concept, will provide highly coherent, ultrashort pulses of soft and hard X-rays with peak intensity many orders of magnitude above that of a synchrotron. These pulses will allow studies of femtosecond dynamics at nanometer resolution and with chemical selectivity. They will produce coherent-diffraction images of organic and inorganic nanostructures without the deleterious effects of radiation damage.

This lecture is an introduction to the generation of plasma-based XUV lasers and their use as a source for scientific applications. We first discuss the main conditions required to create population inversions and amplify XUV radiation. We give an overview of the main properties of the different types of XUV lasers beams that are currently operational worldwide, while comparing them to other ultrashort, high-brightness sources existing in the same spectral range. We discuss recent demonstrations of applications of plasma-based XUV lasers to high-resolution imaging and interaction with matter at high intensity. Finally we conclude with current prospects for extending these sources to shorter wavelength and higher output intensity.

Single-photon ionisation of most atoms and molecules requires short-wavelength radiation, typically in the vacuum-ultraviolet (VUV, λ < 200 nm) or extreme ultraviolet (XUV, λ < 105 nm) region of the electromagnetic spectrum. The first VUV and XUV radiation sources used to study molecular photoabsorption and photoionisation spectra were light sources emitting a broad continuous spectrum, such as high pressure lamps or synchrotrons. Monochromatic VUV and XUV radiation was obtained using diffraction gratings in evacuated monochromators, which resulted in a resolving power ν/Δv of at best 10⁶ (i. e. 0.1 cm^-1 at 100 000 cm^-1), but more typically in the range 10⁴-10⁵ . The invention of the laser and the development of nonlinear optical frequency-upconversion techniques enabled the development of table-top narrow-bandwidth, coherent VUV and XUV laser sources with which VUV photoabsorption, photoionisation and photoelectron spectra of molecules can be recorded at much higher resolution, the best sources having bandwidths better than 50 MHz. Such laser sources are ideally suited to study the structure and dynamics of electronically excited states of atoms and molecules and molecular photoionisation using photoabsorption, photoionisation and photoelectron spectroscopy. This chapter presents the general principles that are exploited to generate tunable narrow-band laser radiation below 200 nm and describes spectroscopic methods such as photoabsorption spectroscopy, photoionisation spectroscopy and threshold photoelectron spectroscopy that relay on the broad tunability and narrow-bandwidth of VUV radiation sources.

Plasma-based seeded soft x-ray lasers (PBSXRL) have the potential to generate high-energy, fully coherent, short pulse beam. Nowadays, PBSXRL have demonstrated experimentally 1 μJ, 1 ps (1 MW) fully coherent, aberration-free pulses. Nevertheless, most exciting applications (as single-shot coherent imaging) require pulses shorter than 200 fs and energy ranging from 10 μJ to several miliJoules. In this chapter we will review the theoretical modelling tools and the results obtained related to this source.

Amplification of short-wavelength radiation is advantageously done across a plasma medium. The latter can be produced either using a powerful pump laser or by means of a capillary discharge. The main advantages of this scheme are the ultra-narrow linewidth (Q ≈ 10,000), the full temporal coherence, and the compact footprint. These figures-of-merit are complementary to those of short-wavelength free-electron lasers (xFEL). xFEL facilities are currently available in a few sites, due to the remarkable cost of construction and operation. After a general introduction on laboratory-scale short-wavelength lasers, a comparison with state-of-art xFEL will be done.

In this chapter we report a desk-top microscopy reaching 50nm spatial resolution in very compact setup using a gas-puff laser plasma EUV source. We present the study of source bandwidth influence on the extreme ultraviolet (EUV) microscope spatial resolution. EUV images of object obtained by illumination with variable bandwidth EUV radiation were compared in terms of knife-edge spatial resolution to study the wide bandwidth parasitic influence on spatial resolution in the EUV microscopy.

X-ray microscopy in the water window has become a valuable imaging tool for a wide field of applications with a resolution in the nanometer regime. The emergence and the development of laboratory based transmission X-ray microscopes (LTXM) can be of great benefit to users, since LTXM provides access to a method previously limited to synchrotron facilities only. In recent years, measuring times in the laboratory have been reduced to the point, where tomography of aqueous cryofixated samples has become feasible. We report on a laboratory full-field transmission X-ray microscope based on a laser induced plasma source located at the Berlin Laboratory for innovative X-ray Technologies. A short introduction on full-field X-ray microscopy in the water window is given. We demonstrate that, with a thin disk laser-system (TDL), which provides an average power of ~15 W a spatial resolution of Δx = 41 nm ± 3 nm (half-pitch) is feasible. An image of a diatom recorded at 15 W average laser power with a magnification of 1125x captured in 5 min is presented.

The coherent diffractive imaging method of ptychography is first reviewed from a general historical perspective. Much more recent progress in extending the method to the 3D scattering geometry and the super-resolution configuration is also described. Ptychography was originally conceived by Walter Hoppe as a solution to the X-ray or electron crystallography phase problem. Although the existence of this type of phase information was clearly evident in the early 1970s, the technique was not implemented at atomic-scale wavelengths until the 1990s, and then only in a way that was computationally inefficient, especially in view of the limited size of computers at that time. Fast and efficient ptychographic algorithms were developed much later, in the mid-2000s. The extremes of crystallography ptychography, which only requires two diffraction patterns, and the Wigner Distribution Deconvolution (WDDC) method, which needs a diffraction pattern for every pixel of the final reconstruction, are described. Very recent work relating to the application of serial iterative to 3D inversion are also described.

The chapter deals with main optical properties of Schwarzschild and Head objectives from the point view of geometrical optics. General approach in the study can be applied to both XUV and visible/IR optical instrumentation.

Review of results, obtained by using recently proposed new imaging detector, based on formation of color centers in LiF crystal and LiF film, for in situ high performance measurements of near-field and far-field properties of soft X-ray lasers (SXRL) beams is presented. Experiments have been carried out with laser-driven transient-collision plasma SXRL and free electron SXRL beams. It was demonstrated that due to favorable combination of high spatial resolution, high dynamic range and wide field of view this technique allows measuring not only intensity distribution across the full beam and in local areas, but also permits to evaluate coherence and spectral distribution of radiation across the beam. Experimental diffraction patterns in the images of periodical structures are analyzed by comparison with the modeled ones in the last case. The estimated accuracy of measurements is between 10-20%.

In this work we present results on the influence of laser pulse duration and irradiating power density on the conversion efficiency (CE) and the ion energy of gadolinium (Gd) laser produced plasmas. Three lasers were used with 10 ns, 150 ps and 140 fs pulse durations. By varying the lasers output energies, experiments could be carried out for a power density range of 10¹¹ - 10¹⁵ W/cm². A maximum CE of 0.4% was achieved within a 0.6% bandwidth in 2π steradians using the picosecond laser. A faraday cup was used to calculate ion yield and time of flight measurements of each laser. The picosecond laser also showed a reduction in the ion time of flight measurements compared with the nanosecond pulse.

Elemental analysis by means of X-ray fluorescence (XRF) spectrometry is based on the element-specific electro- magnetic radiation induced as a consequence of inner-shell ionization. XRF spectrometry is ideal for the direct analysis of solid samples, but can also investigate fluid samples. On one side, these methods allow the rapid qualitative screening of unknown samples, without any particular sample preparation. On the other hand, it is possible to perform the fully automated quantitative analysis of large sample sets. Further figures of merit are the ’standard-less’ analysis of samples in a non-destructive mode, and detection down to 0.01 %. The availability of portable XRF systems6 is a further advantage for on-site measurements. The fundamentals are discussed to orient the user, and a survey of instrumental capabilities is provided.

X-ray spectroscopy is a powerful tool for diagnosing the emission characteristics of X-ray sources. It may also be used in characterizing the elemental and chemical states present in compound materials, including the spatial distribution of these states – spectromicroscopy. This paper describes the appropriate spectroscopic techniques along with examples of their uses – the characterization of laser-plasma sources and the study of chemical state distributions in medium density fibreboard. The possibility of using laboratory-scale sources for spectromicroscopy, as opposed to synchrotrons, are discussed, taking into account the signal to noise ratios that are required to provide the necessary precision.

The chapter addresses microscopy with plasma based laboratory extreme ultraviolet (EUV) and soft-x-ray sources. The focus is set on the determination of necessary source parameters like radiance and size from fundamental considerations of the achievable sample resolution, image contrast, detector quantum efficiency and required throughput. The estimations account for the influence of photon noise on signal detection and conservation of light etendue and radiant flux. Two cases are considered more detailed – resolution optimized bright field microscopy and sensitivity optimized dark field microscopy. Inspection of EUV masks and mask blanks required for EUV lithography at 13.5 nm wavelength is chosen as an illustration for both cases.