This PDF file contains the front matter associated with SPIE Proceedings Volume 11111, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

Plasma-based soft x-ray lasers (SXRL) enable experiments requiring bright, high energy, soft x-ray laser pulses to be conducted in compact facilities. Recent advances in high energy, high repetition rate, ultrashort pulse solid state lasers now make it possible to extend their wavelenght range, increase their repetition rates, and improve their efficiency. Recently we extended the operation of gain-saturated compact repetitive x-ray lasers down to λ=6.85 nm in Ni-like Gd [1]. Isoelectronic scaling of these collisionally excited laser transitions produced strong lasing at 6.67 nm and 6.11 nm in Ni-like Tb and amplification at 6.41 nm and 5.85 nm in Ni-like Dy [1]. This recent progress will be summarized, and efforts to further extend laser operation to shorter wavelengths will be reviewed. We will also discuss the possibility of increasing the efficiency of plasma-based soft x-ray lasers by controlling the pulse shape of the pump pulses. Prospects of these SXRL will be discussed. Work supported by the US Department of Energy Basic Energy Sciences and by the National Science Foundation [1] A. Rockwood, Y. Wang, S. Wang, M. Berrill, V.N. Shlyaptsev, and J.J. Rocca, "Compact gain-saturated x-ray lasers down to 6.85 nm and amplification down to 5.85 nm". Optica. 5, 257, (2018).

In this paper we present the modelling work currently performed at the Instituto de Fusión Nuclear “Guillermo Velarde” (Universidad Politécnica de Madrid) in the field of plasma amplifiers of UV, XUV and soft X-ray radiation. Hydrodynamic simulations are performed with ARWEN. The amplification of radiation is studied with 1D (DeepOne), and 3D (Dagon) Maxwell-Bloch codes. Results on hydrodynamic modelling of QSS and OFI soft X-ray lasers, characterization of plasma waveguides and amplification of harmonics in plasmas will be presented.

Modern table-top x-ray plasma lasers produce high energy pulses (up to several mJ) but of rather long picosecond duration. It limits their application for dynamical imaging of fast processes in nanostructures and micromolecules, including the processes induced by the laser radiation. Recently the possibility of an efficient transformation of a picosecond X-ray pulse into a train of subfs pulses in resonant absorber with a transition frequency modulated by an IR field has been shown [1]. Here we suggest two new approaches for generation of the intense attosecond pulses by the X-ray plasma lasers in the soft x-ray range: (i) seeding of the x-ray plasma based laser with a train of attosecond pulses produced via high-harmonic (HH) generation, and (ii) generation of the attosecond pulses directly by the x-ray laser. Both approaches can be achieved via interaction of the x-ray plasma laser radiation or the high-harmonic radiation, accordingly, with the resonant medium modulated by a moderately strong IR or visible laser field similar to [1]. However, contrary to [1], the case of the multicomponent incident radiation, as well as the case of two stage amplifier, allowing for generation of attosecond pulses in the absence of any seeding radiation are studied. In particular, the possibility to amplify about 100 times an incident train of attosecond pulses (produced via HHG) with a pulse duration down to 150 as and a carrier wavelength 3.38nm (in a “water window” range) is shown

Many resonant photo-pumped X-ray laser schemes that use a strong pump line such as Ly-α or He-α to populate the upper laser state of a separate lasing material have been proposed over the last four decades but none have been demonstrated. As a first step to creating a photo-pumped X-ray laser we decided to reinvestigate some of these schemes at the Orion laser facility with the goal to demonstrate enhanced fluorescence as a first step toward creating a laser. In particular we look at using the Ly-α or He-α K lines to pump the 1s – 3p and 4p transitions in H-like Cl and see fluorescence on the 4f -3d line at 65 Å and the 3d – 2p line at 23 Å. Preliminary experiments are presented that show a modest enhancement of 40% on the 3d-2p line. As an alternative we also look at enhancing the 2p – 2s line in Ne-like Ge at 65Å using the Ly-α Mg line to photo-pump the 2s – 3p line of Ne-like Ge. Calculations are presented that suggest modest enhancements of 2.5 and recent experiments will be presented that show emission from a Ge plasma pumped by the Ly-α Mg line.

A capillary laser with output in the extreme ultra-violet at wavelength 46.9 nm is used to ablate solid targets of parylene- N (CH), PMMA, aluminum and gold. We summarize results obtained using different focusing optics: a Fresnel zone plate, an off-axis spherical multi-layer mirror and on-axis multi-layer and gold mirrors. The Fresnel zone plate has a small aperture and focuses a small fraction of the laser energy to a small diameter (< 1 μm) with peak intensities 6 x 10⁹Wcm^-2. The off-axis spherical multi-layer mirror allows for a measurement of the transmission of the laser through thin targets, but the off-axis geometry produced an aberrated focus. The on-axis multi-layer mirror allows focusing to intensities of approximately 5 x 10¹⁰ Wcm^-2 with a cylindrically symmetric focus.

Laser pulses can probe any material, even the more chemically refractory ones. The scaling to ever smaller material sizes demands the utilization of lasers well below commercially available UV lasers, e.g. excimers or frequency quadrupled/quntipled Nd:YAG. While using plasma-driven XUV lasers, the drastic reduction of sampled volume is not accompanied by a reduction in sensitivity, which indicates an enhancement of the sample utilization efficiency using XUV. A capillary discharge Ne-like Ar laser operating 46.9nm was utilized demonstrating unprecedented insights. The rapid direct and absolute characterization in 3D of the elemental distribution using XUV laser – mass spectrometry is shown here in the case of solar thin films. Elements such as suphur, zinc and selenium showed similar layered concentration, while sodium, calcium, and silicon may have diffused from the soda-lime glass substrate. Lithium was doped, and is responsible for the development of a granular porous fabric.

In EUV TOF MS, bright laser pulses from a compact 46.9-nm-wavelength laser [1] are focused into nanometer size spots to ablate craters a few nanometers deep on selected regions of the sample. Elemental and molecular ions in the laser-created plasma are extracted and identified by their mass-to-charge ratio (m/z) using a time-of-flight (TOF) mass spectrometer. Analysis of the spatially resolved mass spectra obtained as the sample is displaced with respect to the focused laser beam enables one to construct 3-D composition images with nanoscale resolution [2]. In this talk I will describe recent advances of extreme ultraviolet MSI that show its unique capabilities to identify low concentration of high Z elements into glass matrices, and to map isotopic ratios [3]. [1] S. Heinbuch et al, "Demonstration of a desk-top size high repetition rate soft x-ray laser," Opt. Express 13, 4050-4055 (2005). [2] I. Kuznetsov et al, "Three dimensional nanoscale molecular imaging by extreme ultraviolet laser ablation mass spectrometry, " Nature Communications, Vol. 6, Article No. 6944(2015). [3] T. Green, et al, “Characterization of extreme ultraviolet laser ablation mass spectrometry for actinide trace analysis and nanoscale isotopic imaging,” J. Analy. At. Spectrom. Vol. 32, 1092 (2017).

In this talk, I would like to introduce and summarize specific features of an interaction of intense short-wavelength, i.e., extreme ultraviolet, soft x-ray and x-ray, radiation with matter. Both plasma and e-beam based sources of coherent XUV/x-ray radiation will be reviewed with respect to performing interaction experiments with their beams. An influence of beam characteristics, i.e., radiation wavelength, pulse duration, wave-front quality, coherence and irradiance, on interaction processes would be discussed in details. A response of various systems, from aluminum targets via plasmid DNA to gases, to short and ultra-short pulses of XUV/x-ray radiation will be described. In conclusion, a comparison of these findings with results obtained in such systems with long-wavelength lasers and conventional sources of ionizing radiation will be presented.

We report on the development and implementation of a diagnostic for the temporal characterization of ultra- short XUV pulses with a single-shot capability. The method which relies on laser-dressed photoionization in a home-made velocity map-imaging spectrometer was implemented on a HHG beamline based on a plasma mirror.

X-ray microscopy has proven its advantages for resolving nanoscale objects. High Harmonic Generation (HHG) sources allow performing nanoimaging experiments at the lab scale and their femtosecond pulse duration and synchrony to an optical laser renders them useful for studying dynamic processes. HHG sources regularly provide high average photon flux but relatively low single-shot flux limiting time-resolved applications to adiabatic processes. Here, we show that soft X-ray lasers (SXRL) in turn provide high flux due to an X-ray lasing transition, but the coherence of an SXRL operating in the amplified-spontaneous-emission scheme is limited. The coherence properties of an SXRL seeded by an HHG source can be significantly improved allowing single-shot nanoscale imaging. In combination with ptychography, source properties are measured with high fidelity. This is applied to study the plasma dynamics of SXRL amplification in unprecedented quality.

With the advent of Diffraction Limited Storage Rings (DLSR) and the Free Electron Lasers (FEL), the challenge for optical designers is to achieve diffraction-limited spot in the experimental chamber preserving the wavefront. This improvement permits working out of focus with almost uniform beam. To reach this level of quality on the beam, one should go behind the Marechal Criterion, stating that a Strehl Ratio (SR, e.g. the ratio between the intensity on the spot for a perfect optical system and the actual one) of 0.8 is a synonymous of a well performing optic system. In reality, a Strehl ratio in excess of 0.95 is needed for wavefront preserving purposes. This corresponds having long mirrors polished at a precision of better than 1 nm rms. With the initial upgrade of the photon transport system of LCLS we demonstrated that it is possible to have an “almost” perfect beam out of focus putting proper attention to all the details and, aiming for a SR of 0.97. But, besides the high precision shape error, some other details shall be considered. For instance, how many beam sigma one should consider for the specifying his mirror and, also, does the slope errors play any role in the quality of the beam out of focus? Moreover, with the advent of SXR DLSRs, it’s important to understand the requirements for the gratings, behind the shape and slope errors, e.g. on the precision of the groove placement. Also, in this case, the Strehl Ratio is a good way for assessing this problem.

Beam conditioning CRL transfocator optics implemented at the Materials Imaging and Dynamics (MID) instrument of the European XFEL are described. Two CRL transfocator units are equipped with beryllium parabolic refractive lenses of large radii of curvature to provide collimated or focused x-ray beam in the 5–25 keV photon energy range. Optical schemes, design and performance of the CRL units, which were recently installed at the SASE2 photon tunnels, are presented.

Three main paths are being developed within the ELI research program for transforming driving laser pulses into bursts of bright short wavelength radiation: high-order harmonic generation in gases, plasma X-ray sources and sources based on relativistic electron beams accelerated in laser plasma. For each of these research areas, dedicated beamlines are built to provide a unique combination of X-ray sources to the scientific community. The application of these beamlines has a well-defined balance between fundamental science and applications in different fields of science and technology. Here we summarize the current status of those user beamlines and we introduce new diagnostics devices developed within the implementation phase of the project, namely compact XUV spectrometer and beam profiler that is using only one fixed detector and an imaging Michelson interferometer with increased sensitivity for low density gas jet characterization.

APOLLON laser facility was initiated by Nobel Laureat Gérard Mourou to become one of the few European 10 PW laser facilities. End of 2018, APOLLON reached 1 PW peak power. Experiments at this power are under preparation with an expected start during spring 2019 or early summer. In parallel, today the laser is under upgrade for reaching 10 PW in few years with an intermediate step at around 5 PW dedicated to the development of experiments at this high power. APOLLON will be open for external users on 2020 at 1 PW and very likely on 2021 at several PW. APOLLON has two experimental areas on which X-ray sources will be developed. The so-called "Long focal length area" (LFA) is dedicated to electron acceleration and related X-ray emission. The room may accommodate focal length up to 9m. The experiments are designed in a way to allows single or double stage electron acceleration with expected electron energies reaching several 10's of GeV. X-ray emission from betatron will be used as a diagnostic of electron acceleration processes but will be also developed independently aiming at achieving energetic and well-collimated X-ray beam. The experiment has been set in a way to allows heads-on electron-laser collision for Compton scattering experiments. The second target area called "Short Focal area", aims at achieving intensities as high as possible for electron and ion acceleration, non-linear QED tests and X-ray generation through high harmonic generation on solid. X-ray emission ranging up to 10 keV is foreseen, with very high peak power at lower energy.

In this paper, we provide an overview of state-of-the-art technologies for incoherent laser-produced tin plasma extreme-ultraviolet (EUV) sources at 13.5nm with performance enabling high volume semiconductor manufacturing (HVM). The key elements to development of a stable and reliable source that also meet HVM throughput requirements and the technical challenges for further scaling EUV power to increase productivity are described. Improvements in availability of droplet generation and the performance of critical subsystems that contribute to EUV collection optics lifetime toward the one tera-pulse level, are shown. We describe current research activities and provide a perspective for EUV sources towards the future ASML Scanners.

Conventional solid-density laser-plasma targets quickly ionize to make a plasma mirror, which largely reflects ultra-intense laser pulses. This Fresnel reflection at the plane boundary largely wastes our e orts at ultra-intense laser/solid interaction, and limits target heating to nonlinear generation of high-energy electrons which penetrate inward. One way around this dual problem is to create a material with an anisotropic dielectric function, for instance by nanostructuring a material in such a way that it cannot support the material responses which generate a specularly reflected beam. We present linear theory for metallic and plasma nanowires, particle-incell simulations of the interaction of ultra-intense femtosecond pulses with nickel nanowires, showing penetration of laser light far deeper than a nickel skin-depth, helping to uniformly heat near-solid material to conditions of high energy-densities, and XFEL experiments giving insight into their ionization and excitation.