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The journal of physical chemistry / A 125, 10138���10143 (2021). doi:10.1021/acs.jpca.1c06033, We performed a time-resolved spectroscopy experixment on the dissociation of oxygen molecules after the interactionwith intense extreme-ultraviolet (XUV) light from the free-electronlaser in Hamburg at Deutsches Elektronen-Synchrotron. Using anXUV-pump/XUV-probe transient-absorption geometry with asplit-and-delay unit, we observe the onset of electronic transitionsin the O$^{2+}$ cation near 50 eV photon energy, marking the end ofthe progression from a molecule to two isolated atoms. We observetwo different time scales of 290 �� 53 and 180 �� 76 fs for theemergence of different ionic transitions, indicating differentdissociation pathways taken by the departing oxygen atoms.With regard to the emerging opportunities of tuning the centralfrequencies of pump and probe pulses and of increasing the probe���pulse bandwidth, future pump���probe transient-absorptionexperiments are expected to provide a detailed view of the coupled nuclear and electronic dynamics during molecular dissociation, Published by Soc., Washington, DC

Nature Communications 12(1), 643 (1-7) (2021). doi:10.1038/s41467-020-20846-1, High-intensity ultrashort pulses at extreme ultraviolet (XUV) and x-ray photon energies, delivered by state-of-the-art free-electron lasers (FELs), are revolutionizing the field of ultrafast spectroscopy. For crossing the next frontiers of research, precise, reliable and practical photonic tools for the spectro-temporal characterization of the pulses are becoming steadily more important. Here, we experimentally demonstrate a technique for the direct measurement of the frequency chirp of extreme-ultraviolet free-electron laser pulses based on fundamental nonlinear optics. It is implemented in XUV-only pump-probe transient-absorption geometry and provides in-situ information on the time-energy structure of FEL pulses. Using a rate-equation model for the time-dependent absorbance changes of anionized neon target, we show how the frequency chirp can be directly extracted and quantified from measured data. Since the method does not rely on an additional external field, we expect a widespread implementation at FELs benefiting multiple science fields by in-situ on-target measurement and optimization of FEL-pulse properties., Published by Nature Publishing Group UK, [London]

A split-and-delay unit for the XUV and soft X-ray spectral range has been installed at beamlines FL23 and FL24 at the FLASH2 Free-Electron Laser at DESY. It enables time-resolved pump-probe experiments covering the whole spectral range of FLASH2 from 30 eV up to 1500 eV. Using wavefront beam splitting and grazing incidence mirrors a sub-fs resolution with a relative pulse delay of -5 ps ≤ uτ ≤ +18 ps is achieved. Two different mirror coatings are required to cover the complete spectral range and thus, a design that is based on a three dimensional beam path was developed. This allows the choice between different sets of mirrors with either coating for the fixed branch. In the variable branch two coatings are available on the same set of mirrors. A Ni coating allows a total transmission above T > 0.50 for photon energies between hν ≈ 30 eV and 650 eV at a grazing angle of a ϑvariable = 1.8° in the beam path with variable delay. With a Pt coating a transmission of T > 13 % is possible for photon energies up to hν = 1500 eV. In the fixed beam path at a grazing angle of ϑfixed = 1.3° a transmission of T > 60 % with a Ni coating and T > 28 % with a Pt coating is possible.

This paper describes a detailed simulation of the influence of optical imperfections in a multilayer Bragg mirror-based split-and-delay unit on the focused and unfocused beam profiles with relative time delays within the coherence time for hard X-ray pump/X-ray probe experiments at the European XFEL., For the High-Energy-Density (HED) beamline at the SASE2 undulator of the European XFEL, a hard X-ray split-and-delay unit (SDU) has been built enabling time-resolved pump/probe experiments with photon energies between 5 keV and 24 keV. The optical layout of the SDU is based on geometrical wavefront splitting and multilayer Bragg mirrors. Maximum delays between Δτ = ±1 ps at 24 keV and Δτ = ±23 ps at 5 keV will be possible. Time-dependent wavefront propagation simulations were performed by means of the Synchrotron Radiation Workshop (SRW) software in order to investigate the impact of the optical layout, including diffraction on the beam splitter and recombiner edges and the three-dimensional topography of all eight mirrors, on the spatio-temporal properties of the XFEL pulses. The radiation is generated from noise by the code FAST which simulates the self-amplified spontaneous emission (SASE) process. A fast Fourier transformation evaluation of the disturbed interference pattern yields for ideal mirror surfaces a coherence time of τc = 0.23 fs and deduces one of τc = 0.21 fs for the real mirrors, thus with an error of Δτ = 0.02 fs which is smaller than the deviation resulting from shot-to-shot fluctuations of SASE2 pulses. The wavefronts are focused by means of compound refractive lenses in order to achieve fluences of a few hundred mJ mm−2 within a spot width of 20 µm (FWHM) diameter. Coherence effects and optics imperfections increase the peak intensity between 200 and 400% for pulse delays within the coherence time. Additionally, the influence of two off-set mirrors in the HED beamline are discussed. Further, we show the fluence distribution for Δz = ±3 mm around the focal spot along the optical axis. The simulations show that the topographies of the mirrors of the SDU are good enough to support X-ray pump/X-ray probe experiments.

Physical review / X 11(3), 031001 (1-9) (2021). doi:10.1103/PhysRevX.11.031001, In this work, we use an extreme-ultraviolet (XUV) free-electron laser (FEL) to resonantly excite the I: 4$d_{5/2}–σ^∗$ transition of a gas-phase di-iodomethane (CH$_2$I$_2$) target. This site-specific excitation generates a 4$d$ core hole located at an iodine site, which leaves the molecule in a well-defined excited state. We subsequently measure the time-dependent absorption change of the molecule with the FEL probe spectrum centered on the same I: 4$_d$ resonance. Using ab initio calculations of absorption spectra of a transient isomerization pathway observed in earlier studies, our time-resolved measurements allow us to assign the timescales of the previously reported direct and indirect dissociation pathways. The presented method is thus sensitive to excited-state molecular geometries in a time-resolved manner, following a core-resonant site-specific trigger., Published by APS, College Park, Md.

The emergence of ultra-intense extreme-ultraviolet (XUV) and X-ray free-electron lasers (FELs) has opened the door for the experimental realization of non-linear XUV and X-ray spectroscopy techniques. Here we demonstrate an experimental setup for an all-XUV transient absorption spectroscopy method for gas-phase targets at the FEL. The setup combines a high spectral resolving power of E/ΔE ≈ 1500 with sub-femtosecond interferometric resolution, and covers a broad XUV photon-energy range between approximately 20 and 110 eV. We demonstrate the feasibility of this setup firstly on a neon target. Here, we intensity- and time-resolve key aspects of non-linear XUV-FEL light-matter interactions, namely the non-resonant ionization dynamics and resonant coupling dynamics of bound states, including XUV-induced Stark shifts of energy levels. Secondly, we show that this setup is capable of tracking the XUV-initiated dissociation dynamics of small molecular targets (oxygen and diiodomethane) with site-specific resolution, by measuring the XUV transient absorption spectrum. In general, benefitting from a single-shot detection capability, we show that the setup and method provides single-shot phase-locked XUV pulse pairs. This lays the foundation to perform, in the future, experiments as a function of the XUV interferometric time delay and the relative phase, which enables advanced coherent non-linear spectroscopy schemes in the XUV and X-ray spectral range., Faraday Discussions, 228, ISSN:1359-6640, ISSN:1364-5498

The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter.

We present a technique for the direct measurement of the frequency chirp of high-frequency free-electron-laser pulses based on fundamental nonlinear optics. It is implemented in transient absorption geometry.

Physical review letters 123(10), 103001 (2019). doi:10.1103/PhysRevLett.123.103001, We demonstrate time-resolved nonlinear extreme-ultraviolet absorption spectroscopy on multiply charged ions, here applied to the doubly charged neon ion, driven by a phase-locked sequence of two intense free-electron laser pulses. Absorption signatures of resonance lines due to $2p-3d$ bound–bound transitions between the spin-orbit multiplets $^3P_{0,1,2}$ and $^3D_{1,2,3}$ of the transiently produced doubly charged Ne$^{2+}$ ion are revealed, with time-dependent spectral changes over a time-delay range of (2.4±0.3) fs. Furthermore, we observe 10-meV-scale spectral shifts of these resonances owing to the ac Stark effect. We use a time-dependent quantum model to explain the observations by an enhanced coupling of the ionic quantum states with the partially coherent free-electron laser radiation when the phase-locked pump and probe pulses precisely overlap in time., Published by APS, College Park, Md.

We present an extreme ultraviolet (EUV) microscope using a Schwarzschild objective which is optimized for single-shot sub-micrometer imaging of laser-plasma targets. The microscope has been designed and constructed for imaging the scattering from an EUV-heated solid-density hydrogen jet. Imaging of a cryogenic hydrogen target was demonstrated using single pulses of the free-electron laser in Hamburg (FLASH) free-electron laser at a wavelength of 13.5 nm. In a single exposure, we observe a hydrogen jet with ice fragments with a spatial resolution in the sub-micrometer range. In situ EUV imaging is expected to enable novel experimental capabilities for warm dense matter studies of micrometer-sized samples in laser-plasma experiments.

International audience; The photochemical processing of a CH 4 : D 2 O 1 : 3.3 ice mixture adsorbed on an HOPG surface in the XUV regime was investigated using pulses obtained from the Free-electron LASer in Hamburg (FLASH) facility. Ice films were exposed to femtosecond pulses with a photon energy of hn = 40.8 eV, consistent with the HeII resonance line. Cationic species desorbing directly from the ice films were detected using time-of-flight (ToF) mass spectrometry. Simple ions formed through the fragmentation of the parent molecules and subsequent recombination reactions were detected and are consistent with efficient D + and H + ejection from the parent species, similar to the case for low energy electron irradiation. The FEL fluence dependencies of these ions are linear or exhibit a non-linear order of up to 3. In addition, a series of C n + cluster ions (with n up to 12) were also identified. These ions display a highly non-linear desorption yield with respect to the FEL fluence, having an order of 6-10, suggesting a complex multi-step process involving the primary products of CH 4 fragmentation. Two-pulse correlation measurements were performed to gain further insight into the underlying reaction dynamics of the photo-chemical reactions. The yield of the D 2 O derived products displayed a different temporal behaviour with respect to the C n + ions, indicating the presence of very different reaction pathways to the two families of ionic products.

[Proceedings] - , 2017. - doi:10.1117/12.2265708 Advances in X-ray Free-Electron Lasers Instrumentation IV, Prague, Czech Republic, 24 Apr 2017 - 27 Apr 2017; Proceedings of SPIE 10237, 1023712 (2017). doi:10.1117/12.2265708, For the soft x-ray free-electron laser FLASH II at DESY in Hamburg a new split-and-delay unit (SDU) is built for photon energies in the range of 30 eV < hν < 1500 eV with an option to expand this range to hν = 2500 eV. The SDU is based on wavefront beam splitting at grazing incidence angles. A three dimensional set-up allows for the use of two different beam paths. With grazing angles of θ = 1.3° in the fixed beam paths and θ = 1.8° in the variable beam path a good compromise between a sufficient reflectance (shallow angles) and a large possible maximum delay (steeper angles) has been chosen. The maximum possible delay is -6 ps < Δt < 18 ps. For photon energies in the range of 30 eV < hν < 800 eV the mirrors are coated with Ni providing a total transmission between T = 57 % at hν = 30 eV and still T >; 30 % at hν = 800 eV. For photon energies up to hν = 1800 eV a different beam path with platinum coated mirrors is used enabling a total transmission in the fixed beam path of T > 29 % at hν = 800 eV and T = 24 % at hν = 1800 eV, respectively. In the variable beam path the total transmission in this photon energy range is considerably lower but still sufficient with T = 13 % at hν = 800 eV and T > 6 % at hν = 1800 eV., Published by SPIE, Bellingham, Wash.

Intermolecular reactions in and on icy films on silicate and carbonaceous grains constitute a major route for the formation of new molecular constituents in interstellar molecular clouds. In more diffuse regions and in protoplanetary discs, energetic radiation can trigger reaction routes far from thermal equilibrium. As an analog of interstellar ice-covered dust grains, highly-oriented pyrolytic graphite (HOPG) covered with D2O, NO, and H atoms is irradiated by ultrashort XUV pulses and the desorbing ionic and neutral products are analysed. The yields of several products show a nonlinear intensity dependence and thus enable the elucidation of reaction dynamics by two-pulse correlated desorption.

Researchers demonstrate an X-ray holography method that records two independent images spaced by a femtosecond variable time delay. The concept overcomes the time limitations of two-dimensional area detectors by superimposing the separable X-ray holograms in a single detector exposure.

Structural dynamics 5(5), 054501 (2018). doi:10.1063/1.5042847, We present a general experimental concept for jitter-free pump and probe experiments at free electron lasers. By generating pump and probe pulse from one and the same X-ray pulse using an optical split-and-delay unit, we obtain a temporal resolution that is limited only by the X-ray pulse lengths. In a two-color X-ray pump and X-ray probe experiment with sub 70 fs temporal resolution, we selectively probe the response of orbital and charge degree of freedom in the prototypical functional oxide magnetite after photoexcitation. We find electronic order to be quenched on a time scale of (30 ± 30) fs and hence most likely faster than what is to be expected for any lattice dynamics. Our experimental result hints to the formation of a short lived transient state with decoupled electronic and lattice degree of freedom in magnetite. The excitation and relaxation mechanism for X-ray pumping is discussed within a simple model leading to the conclusion that within the first 10 fs the original photoexcitation decays into low-energy electronic excitations comparable to what is achieved by optical pump pulse excitation. Our findings show on which time scales dynamical decoupling of degrees of freedom in functional oxides can be expected and how to probe this selectively with soft X-ray pulses. Results can be expected to provide crucial information for theories for ultrafast behavior of materials and help to develop concepts for novel switching devices., Published by AIP Publishing LLC, Melville, NY

We use a Mach-Zehnder type autocorrelator to split and delay XUV pulses from the FLASH soft X-ray laser for triggering and subsequently probing the explosion of aerosolised sugar balls. FLASH was running at 182 eV photon energy with pulses of 70 fs duration. The delay between the pump-probe pulses was varied between zero and 5 ps, and the pulses were focused to reach peak intensities above 1016 W/cm2 with an off-axis parabola. The direct pulse triggered the explosion of single aerosolised sucrose nano-particles, while the delayed pulse probed the exploding structure. The ejected ions were measured by ion time of flight spectrometry, and the particle sizes were measured by coherent diffractive imaging. The results show that sucrose particles of 560-1000 nm diameter retain their size for about 500 fs following the first exposure. Significant sample expansion happens between 500 fs and 1 ps. We present simulations to support these observations.

We investigate subpicosecond dynamics of warm dense hydrogen at the XUV free-electron laser facility (FLASH) at DESY (Hamburg). Ultrafast impulsive electron heating is initiated by a â‰300-fs short x-ray burst of 92-eV photon energy. A second pulse probes the sample via x-ray scattering at jitter-free variable time delay. We show that the initial molecular structure dissociates within (0.9±0.2) ps, allowing us to infer the energy transfer rate between electrons and ions. We evaluate Saha and Thomas-Fermi ionization models in radiation hydrodynamics simulations, predicting plasma parameters that are subsequently used to calculate the static structure factor. A conductivity model for partially ionized plasma is validated by two-temperature density-functional theory coupled to molecular dynamic simulations and agrees with the experimental data. Our results provide important insights and the needed experimental data on transport properties of dense plasmas. © 2014 American Physical Society.

A tunable two-color multilayer Bragg coating capable of simultaneously reflecting the fundamental and the third harmonic of an x-ray free-electron laser at the same angle and with high reflectance R > 0.70 is presented. The novel coating will enable two-color x-ray pump/x-ray probe experiments. This mirror consists of a Si substrate that is coated with two different types of multilayer systems, Mo/B4C layers with a periodicity of d = 3.2 nm directly on the substrate and Ni/B4C layers with a periodicity of d = 11.85 nm on top. Fundamental radiation with photon energies between 3 and 9 keV is reflected by a Ni/B4C multilayer system while the third harmonic (9 keV < h nu < 27 keV) passes this system and is reflected by the Mo/B4C multilayers. The principle has successfully been proven at the beamline BM05 at ESRF.

We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300 fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9 ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory. © 2014 American Physical Society.

For the European x-ray free electron laser (XFEL) a split-and-delay unit based on geometrical wavefront beam splitting and multilayer mirrors is built which covers the range of photon energies from 5 keV up to 20 keV. Maximum delays between $\mathrm{\ensuremath{\Delta}}\ensuremath{\tau}=\ifmmode\pm\else\textpm\fi{}2.5\text{ }\text{ }\mathrm{ps}$ at $h\ensuremath{\nu}=20\text{ }\mathrm{keV}$ and up to $\mathrm{\ensuremath{\Delta}}\ensuremath{\tau}=\ifmmode\pm\else\textpm\fi{}23\text{ }\text{ }\mathrm{ps}$ at $h\ensuremath{\nu}=5\text{ }\text{ }\mathrm{keV}$ will be possible. Time-dependent wave-optics simulations have been performed by means of Synchrotron Radiation Workshop software for XFEL pulses at $h\ensuremath{\nu}=5\text{ }\text{ }\mathrm{keV}$. The XFEL radiation was simulated using results of time-dependent simulations applying the self-amplified spontaneous emission code FAST. Main features of the optical layout, including diffraction on the beam splitter edge and optics imperfections measured with a nanometer optic component measuring machine slope measuring profiler, were taken into account. The impact of these effects on the characterization of the temporal properties of XFEL pulses is analyzed. An approach based on fast Fourier transformation allows for the evaluation of the temporal coherence despite large wavefront distortions caused by the optics imperfections. In this way, the fringes resulting from time-dependent two-beam interference can be filtered and evaluated yielding a coherence time of ${\ensuremath{\tau}}_{c}=0.187\text{ }\text{ }\mathrm{fs}$ (HWHM) for real, nonperfect mirrors, while for ideal mirrors a coherence time of ${\ensuremath{\tau}}_{c}=0.191\text{ }\text{ }\mathrm{fs}$ (HWHM) is expected.

For the European XFEL [1] an x-ray split- and delay-unit (SDU) is built covering photon energies from 5 keV up to 20 keV. This SDU will enable time-resolved x-ray pump / x-ray probe experiments as well as sequential diffractive imaging [2] on a femtosecond to picosecond time scale. Further, direct measurements of the temporal coherence properties will be possible by making use of a linear autocorrelation. The set-up is based on geometric wavefront beam splitting, which has successfully been implemented at an autocorrelator at FLASH [3]. The x-ray FEL pulses will be split by a sharp edge of a silicon mirror coated with Mo/B4C multi layers. Both partial beams will then pass variable delay lines. For different wavelengths the angle of incidence onto the multilayer mirrors will be adjusted in order to match the Bragg condition. For a photon energy of hν = 20 keV a grazing angle of θ = 0.57° has to be set, which results in a footprint of the beam (6σ) on the mirror of l = 345 mm. At this photon energy the reflectance of a Mo/B4C multi layer coating with a multi layer period of d = 3 nm and N = 200 layers amounts to R = 0.92. For a photon energy of hν = 5 keV a smaller size of the footprint of l = 244 mm is calculated due to the steeper grazing angle of θ = 2.28°. In order to enhance the maximum transmission for photon energies of hν = 8 keV and below, a Ni/B4C multilayer coating can be applied beside the Mo/B4C coating for this spectral region. Because of the different incidence angles, the path lengths of the beams will differ as a function of wavelength. Hence, maximum delays between +/- 3.7 ps at hν = 20 keV and up to +/- 44 ps at hν = 5 keV will be possible.

Journal of physics / B 46(16), 164005 (2013). doi:10.1088/0953-4075/46/16/164005, For time-resolved extreme ultraviolet (XUV) pump–XUV probe experiments at the Free electron LASer in Hamburg (FLASH), a split-and-delay unit (SDU) has been built. It is implemented in beamline BL2 which provides a focal spot size of about 20 μm diameter in the experiment. The beam is divided geometrically into two paths which can be delayed from −3 to +15 ps with respect to each other. The transmission up to 200 eV photon energy is above 35% in one beam path and 74% in the other. The latter transmits the XUV beam again from 305 to 570 eV (>1% transmission). Thus almost the whole spectral range at FLASH is covered by the SDU with reasonable transmission, including the option to transport high-energy third harmonic radiation in one of the beam paths. Both beam paths are realigned into the original direction of the radiation at the end of the SDU. Thus the utilization of the divided as well as the original beam is enabled by simply moving the optical elements of the SDU into or out of the beam. Using the SDU, the coherence length and the average pulse duration at FLASH was determined to be 0.9–1.8 μm, depending on the wavelength, and about 30 fs, respectively, for the specific electron bunch parameters., Published by IOP Publ., Bristol

This article reviews recent developments in research on coherence properties of femtosecond XUV and x-ray lasers. Coherence is one of the most conspicuous features of laser sources. It describes how an electromagnetic wave field is correlated at different times and at different points in space. Coherence is a property that enables stationary interferences and thereby enables holographic and diffractive or lens less imaging. While a large number of different laser systems radiating in the infrared, visible and UV spectral range have been developed in the past five decades since the invention of the laser, the generation of intense and coherent XUV and x-ray radiation is still a formidable goal of basic research. Developed first in the mid and far infrared spectral region free electron lasers (FEL) provide a new means to generate widely tunable coherent radiation [Madey, 1971; Deacon et al., 1977; Oepts et al., 1995]. In the XUV and soft x-ray spectral region the present lack of appropriate mirrors prevent the construction of optical resonators, essential for a laser with well-defined mode properties. Therefore in this spectral region free-electron lasers have to rely on the principle of self-amplified spontaneous emission (SASE), where in a single path enough gain is accumulated to evolve a pulse from shot noise. These machines then provide pulsed XUV and x-ray radiation which shows only partial coherence (Kondratenko & Saldin, 1980; Bonifacio et al., 1984; Murphy & Pellegrini, 1985). A characterisation of the coherence properties of SASE FEL radiation is not only important for the understanding and improvement of the SASE process. With the concomitant development of coherent diffraction imaging it is also of great practical importance in a broad field of fundamental scientific applications, like holographic imaging of artificial magnetic structures or single pulse imaging of large biomolecules. The theoretical description of the coherence properties of SASE FEL has made tremendous progress in the recent years. In this chapter we will briefly review measurement methods and description of partially coherent optical fields. The considerations will be applied to characterize the spatial and temporal coherence of pulses from the SASE free electron laser in Hamburg (FLASH) and of high harmonic radiation.

To provide two jitter‐free soft x‐ray pulses for femtosecond x‐ray pump and probe experiments a split and delay unit (autocorrelator) has been constructed for the VUV—FEL in Hamburg (FLASH). Here we report experiments applying this autocorrelator to examine the average temporal properties of FEL pulses delivered from FLASH at 24 nm (51.8 eV). In a linear autocorrelation experiment the spatio‐temporal coherence properties are measured for both the first and the third harmonic of the FEL pulses. Furthermore, we report on the first evaluation of the pulse length from the time‐resolved observation of doubly charged helium ions produced by direct two‐photon double ionization at 24 nm. In summary the determination of the longitudinal pulse parameter of FLASH at 24 nm to 6 fs and 29±5 fs for the coherence time and the pulse length (FWHM) respectively proofs the autocorrelator as a valuable tool for time resolved two pulse X‐ray experiments.

Physical review / A 80(2), 4 (2009). doi:10.1103/PhysRevA.80.025402, The pulse duration of soft x-ray free-electron laser (FEL) radiation is directly measured by time-resolved observation of doubly charged helium ions at 51.8 eV. A wave front splitting autocorrelator produces two correlated FEL pulses with a resolution of better than a femtosecond. In the interesting intensity range from 10$_{13}$ to 10$_{16]$ W/cm$_2$ direct and sequential double ionization contribute to the ion yield which has significant influence on the correlation width, being a general feature at high photon energies. Here, a duration of τL=(29±5) fs is derived for the soft x-ray pulses at FLASH., Published by APS, College Park, Md.

We report first direct measurements of the average temporal coherence and pulse length of soft X-ray fs pulses from the free-electron laser at DESY (FLASH) by means of linear and nonlinear autocorrelation

The temporal coherence properties of soft x-ray free electron laser pulses at FLASH are measured at 23.9 nm by interfering two time-delayed partial beams directly on a CCD camera. The partial beams are obtained by wave front beam splitting in an autocorrelator operating at photon energies from h nu = 30 to 200 eV. At zero delay a visibility of (0.63+/- 0.04) is measured. The delay of one partial beam reveals a coherence time of 6 fs at 23.9 nm. The visibility further displays a non-monotonic decay, which can be rationalized by the presence of multiple pulse structure.

Design Based Metrology (DBM) implements a novel automation flow, which allows for a direct and traceable correspondence to be established between selected locations in product designs and matching metrology locations on silicon wafers. Thus DBM constitutes the fundamental enabler of Design For Manufacturability (DFM), because of its intrinsic ability to characterize and quantify the discrepancy between design layout intent and actual patterns on silicon. The evolution of the CDSEM into a DFM tool, capable of measuring thousands of unique sites, includes 3 essential functionalities: (1) seamless integration with design layout and locations coordinate system; (2) new design-based pattern recognition and (3) fully automated recipe generation. Additionally advanced SEM metrology algorithms are required for complex 2-dimensional features, Line-Edge-Roughness (LER), etc. In this paper, we consider the overall DBM flow, its integration with traditional CDSEM metrology and the state-of-the-art in recipe automation success. We also investigate advanced DFM applications, specifically enabled by DBM, particularly for OPC model calibration and verification, design-driven RET development and parametric Design Rule evaluation and selection.

In this work components of the next generation 0.10 /spl mu/m CMOS technology are presented. They form the core of a platform encompassing logic, non volatile memory, and analog blocks. High performance bulk devices use 18 /spl Aring/ gate oxide (24 /spl Aring/ inversion Tox) while low power devices use 25 /spl Aring/ gate oxide (31 /spl Aring/ inversion Tox) for reduced gate leakage. Gate lengths range from 65 nm for the high performance devices to 90 nm for the low power devices. Both 3.3 V and 2.5 V I/Os are supported using 70 /spl Aring/ and 50 /spl Aring/ oxide devices. The backend employs low-k (k/spl sim/3) dielectric with multiple levels of Cu metallization. The high density 6T SRAM cell size is 1.33 /spl mu/m/sup 2/.

The expansion and disintegration dynamics of xenon clusters initiated by the ionization with femtosecond soft x-ray extreme ultraviolet (XUV) pulses were studied with pump–probe spectroscopy using the autocorrelator setup of the Free-Electron LASer in Hamburg (FLASH) facility. The ionization by the first XUV pulse of 92 eV photon energy (8 × 10 12 Wc m −2 ) leads to the generation of a large number of quasi-free electrons trapped by the space charge of the cluster ions. A temporally delayed, more intense probe (4 × 10 13 Wc m −2 ) pulse substantially increases a population of nanoplasma electrons providing a way of probing plasma states in the expanding cluster by tracing the average charge of fragment ions. The results of the study reveal a timescale for cluster expansion and disintegration, which depends essentially on the initial cluster size. The average charge state of fragment ions, and thus the cluster plasma changes significantly on a timescale of 1–3 ps. (Some figures may appear in colour only in the online journal)

Femtosecond pulse x-ray imaging is demonstrated in a sample-multiplexed Fourier transform holography scheme. Parallel imaging of multiple samples over an extended field of view is achieved by exploiting the coherence properties of the free-electron laser (FEL) source and the large profile of the unfocused x-ray pulse. The resulting photon flux density per pulse allows for damage-free single-pulse imaging with moderate image resolution. We envision the application of the method for femtosecond time-resolved pump–probe experiments with the feasibility of recording multiple steps in time with a single pulse. Furthermore, the scheme presented allows for a characterization of FEL radiation pulse parameters.