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Dynamics of interatomic Coulombic decay in neon dimers by XUV-pump–XUV-probe spectroscopy
摘要： We apply the Monte Carlo wave-packet approach to study the interatomic Coulombic decay (ICD) dynamics of neon dimers after removing a 2s electron from one of the Ne atoms by one-photon absorption from an XUV pulse. This method reproduces well both the lifetime for the 2s inner-valence vacancy in Ne2+(2s?1) and the kinetic energy release (KER) spectra for the coincident Ne+ and Ne2+ fragments following triple ionization, i.e., two photoionizations and one ionization via ICD, of Ne2 measured in an XUV-pump–XUV-probe experiment [K. Schnorr et al., Phys. Rev. Lett. 111, 093402 (2013)]. Comparisons between the calculated and measured nuclear KER spectra give physical insights in the considered process. For example, an analysis of the ratios between the low- and high-energy peaks in the nuclear KER spectra for large delays provides an estimate of the photoionization cross sections for removing a 2p electron from the excited states in Ne2+(2s?1). Such comparisons also allow an estimate for the ICD rates for the 2s inner-valence vacancy in the single-site two-hole state in Ne2+(2s?12p?1). Finally, the influence of photon statistics of the free electron laser pulses on the nuclear KER spectra is considered.
关键词： neon dimers,interatomic Coulombic decay,kinetic energy release spectra,XUV-pump–XUV-probe spectroscopy,Monte Carlo wave-packet approach
更新于2025-09-23 15:23:52
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Progress in development of a new luminescence setup at the FinEstBeAMS beamline of the MAX IV laboratory
摘要： FinEstBeAMS is a new materials science beamline at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It has been built based on grazing incidence monochromatization of synchrotron light, which allows to cover a remarkably wide excitation energy range from ultraviolet to soft x-rays (4.5-1450 eV). A new mobile luminescence spectroscopy end station has been commissioned with design benefitting from the advantages of a high flux elliptically polarizing undulator light source. We report on the design of the luminescence end station, its technical realization and performance achieved so far. Special attention is paid to the experimental challenges for luminescence spectroscopy under grazing incidence excitation conditions. The first luminescence results obtained demonstrate a reliable performance of the advanced setup at FinEstBeAMS.
关键词： Luminescence spectroscopy,synchrotron radiation,wide gap compounds,VUV – XUV photoexcitation
更新于2025-09-23 15:23:52
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Pressure dependence of high order harmonic generation in nitrogen molecular gas and atmospheric air
摘要： The effect of the variation of the gas pressure on the high harmonic generation (HHG) from nitrogen molecular gas (N2) and atmospheric air with ultrashort intense laser pulses is measured. The optimum pressure in the interaction region of a gas jet for maximizing the HHG yield is determined for both gases. Enhancement of the HHG output and its extension to higher harmonic orders are observed around the optimum pressure value of 0.33 bar. Theoretical calculations based on one-dimensional models explain this effect and provide reasonable agreement with experimental results.
关键词： Femtosecond laser,Conversion efficiency,High-order harmonic generation (HHG),Phase matching,XUV radiation,Pressure optimization
更新于2025-09-23 15:23:52
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Polarization-Dependent Self-Injection by Above Threshold Ionization Heating in a Laser Wakefield Accelerator
摘要： We report on the experimental observation of a decreased self-injection threshold by using laser pulses with circular polarization in laser wakefield acceleration experiments in a nonpreformed plasma, compared to the usually employed linear polarization. A significantly higher electron beam charge was also observed for circular polarization compared to linear polarization over a wide range of parameters. Theoretical analysis and quasi-3D particle-in-cell simulations reveal that the self-injection and hence the laser wakefield acceleration is polarization dependent and indicate a different injection mechanism for circularly polarized laser pulses, originating from larger momentum gain by electrons during above threshold ionization. This enables electrons to meet the trapping condition more easily, and the resulting higher plasma temperature was confirmed via spectroscopy of the XUV plasma emission.
关键词： self-injection,Laser wakefield acceleration,XUV spectroscopy,above threshold ionization,polarization
更新于2025-09-23 15:19:57
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Ghost imaging at an XUV free-electron laser
摘要： Here we present the results of a classical ghost imaging experiment accomplished at an XUV free-electron laser (FEL). To perform such experiment at an FEL source each x-ray pulse was transmitted through a moving diffuser, which created a noncorrelated speckled beam. This beam was then split in two identical branches by introducing a beam splitter in the form of a transmission grating. In one of these branches the sample was positioned. We demonstrate the possibility of image formation, a double bar in our case, in the beam that has never interacted with the sample. With this experiment we extend the quantum optics methodology to the FEL community.
关键词： XUV free-electron laser,speckle pattern,quantum optics,ghost imaging,transmission grating
更新于2025-09-23 15:19:57
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Selection of the magnetic quantum number in resonant ionization of neon using an XUV-IR two-color laser field
摘要： A recent experiment [Villeneuve et al. Science 356, 1150 (2017)] has shown that two-color photoionization of neon by the combination of an attosecond XUV pulse train and a moderately strong, linearly polarized IR pulse can preferentially produce photoelectrons with orbital angular quantum number l = 3 (f-wave) and magnetic quantum number m = 0. This result was rationalized by the occurrence of different Stark shifts of m = 0 and |m| = 1 sub-levels in the IR laser field. Here we perform 3D time-dependent Schrodinger equation calculations with a neon effective potential to identify the mechanism for the selective excitation and ionization of m = 0 sub-levels. Calculations of the ionization and excitation yields as a function of the IR intensity and the XUV and IR photon energy reveal that a coupling between two dominant ionization channels involving 3p and 3d intermediate excitations is responsible for the observed m-level selectivity. We compare calculated and measured photoelectron velocity map images and ionization yields over a range of IR intensities and XUV and IR photon energies, and confirm that the m = 0 or |m| = 1 channel, and thus a single set of the quantum numbers, (Jion, l, m), can be selected by an appropriate choice of these parameters.
关键词： photoelectron velocity map images,XUV-IR laser field,neon,time-dependent Schrodinger equation,two-color photoionization,magnetic quantum number,Stark shifts
更新于2025-09-23 15:19:57
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Stimulated resonant inelastic x-ray scattering with chirped, broadband pulses
摘要： We present an approach for initiating and tracing ultrafast electron dynamics in core-excited atoms, molecules, and solids. The approach is based on stimulated resonant inelastic x-ray scattering induced by a single, chirped, broadband XUV or x-ray pulse. A first interaction with this pulse prepares a core-excited state wave packet by resonant core-excitation. A second interaction with the pulse at a later time induces the transition to valence-excited states, which is associated with stimulated emission. The preparation of the core-excited wave packet and the transition from the core-excited states to the valence-excited states occur at distinct chirp-dependent times. As a consequence, the stimulated emission carries information about the time evolution of the core-excited state wave packet.
关键词： XUV pulses,x-ray pulses,core-excited states,ultrafast electron dynamics,chirped pulses,stimulated resonant inelastic x-ray scattering
更新于2025-09-19 17:15:36
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Multi-parameter optimization of a loose focusing high flux high-harmonic beamline
摘要： We perform a multi-dimensional parameter scan in the generation of high-order harmonics, with the main purpose to find the macroscopic conditions that optimize the harmonic yield in a specific spectral domain, around 40 eV for this particular case. The scanned parameters are the laser pulse energy, gas pressure, interaction cell position relative to focus and the cell length, while the fixed parameters are chosen to model a loose focusing configuration which is used in many existing laboratories. We performed the simulations with a 3D non-adiabatic model complemented by a detailed analysis of the phase matching mechanisms involved in an efficient harmonic generation. Based on the results we identify a range of parameter combinations that lead to a high yield in the specified spectral domain. The method and results presented here can be the framework for the design and construction of high flux high-order harmonic generation beamlines.
关键词： XUV flux,high-order harmonic generation,optimization,multi-dimensional parameter scan,numerical simulation
更新于2025-09-19 17:15:36
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Growth of Atomic Layer Deposited Ruthenium and Its Optical Properties at Short Wavelengths Using Ru(EtCp)2 and Oxygen
摘要： High-density ruthenium (Ru) thin films were deposited using Ru(EtCp)2 (bis(ethylcyclopentadienyl)ruthenium) and oxygen by thermal atomic layer deposition (ALD) and compared to magnetron sputtered (MS) Ru coatings. The ALD Ru film growth and surface roughness show a significant temperature dependence. At temperatures below 200 °C, no deposition was observed on silicon and fused silica substrates. With increasing deposition temperature, the nucleation of Ru starts and leads eventually to fully closed, polycrystalline coatings. The formation of blisters starts at temperatures above 275 °C because of poor adhesion properties, which results in a high surface roughness. The optimum deposition temperature is 250 °C in our tool and leads to rather smooth film surfaces, with roughness values of approximately 3 nm. The ALD Ru thin films have similar morphology compared with MS coatings, e.g., hexagonal polycrystalline structure and high density. Discrepancies of the optical properties can be explained by the higher roughness of ALD films compared to MS coatings. To use ALD Ru for optical applications at short wavelengths (λ = 2–50 nm), further improvement of their film quality is required.
关键词： optical properties,sputtering,structural properties,XUV,ruthenium,soft X-ray,thin film,atomic layer deposition
更新于2025-09-19 17:15:36
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Soft X-ray laser ablation for nano-scale chemical mapping microanalysis
摘要： Laser-assisted microanalysis offers the advantage of determining the spatially resolved compositions in 3D. Scanning a material with a sequence of sampling laser pulses and acquiring online the related spectra allow one to map the lateral and depth distribution of elements and molecules. However, the requirement to analyse smaller and smaller length-scales is challenged by focal diffraction as well as reduction of the nano-scale. Electron-based microprobes still offer unmatched spatial resolution. Disruptive improvements in laser technology are however demonstrated utilizing recently self-developed extreme ultraviolet or soft X-ray lasers. Firstly, a significant enhancement of the resolution is accomplished thanks to a much shorter wavelength, with respect to state-of-the-art commercial lasers. Furthermore, as the most innovative aspect, the sampling efficiency is enhanced using 'ionizing radiation', i.e. directly activating the target material. The high photon-energy (20–100 eV) makes the sampling process essentially single-photon, whatever bond or ionization energy. Furthermore, the analytical setup is simplified to a sampling source and detector, i.e. without the need for a secondary ionization or excitation source as in some state-of-the-art analytical systems. In this review, fundamental aspects of X-ray laser desorption and ablation are discussed, and a survey of the available literature is presented. The main objective is to convince the reader that desorption or ablation in this spectral domain is a significantly cleaner sampling process, with large potential, still requiring investigation for a complete fundamental understanding. Applications of laser microanalysis are thus entering the nano-scale era, which shrinks the gap with electron-based microprobes.
关键词： Laser-assisted microanalysis,XUV/SXR lasers,ablation,single-photon sampling,nano-scale chemical mapping,desorption
更新于2025-09-19 17:13:59