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We study the dynamics of avalanche ionization of pure helium nanodroplets activated by a weak extreme-ultraviolet (XUV) pulse and driven by an intense near-infrared (NIR) pulse. In addition to a transient enhancement of ignition of a nanoplasma at short delay times ~200 fs, long-term activation of the nanodroplets lasting up to a few nanoseconds is observed. Molecular dynamics simulations suggest that the short-term activation is caused by the injection of seed electrons into the droplets by XUV photoemission. Long-term activation appears due to electrons remaining loosely bound to photoions which form stable `snowball' structures in the droplets. Thus, we show that XUV irradiation can induce long-lasting changes of the strong-field optical properties of nanoparticles, potentially opening new routes to controlling avalanche-ionization phenomena in nanostructures and condensed-phase systems.

With this study, we present the development of a transportable x‐ray emission spectrometer (XES) that was realized in a net time of 20 h, in order to verify the presence of Platinum (Pt) in gold Celtic coins belonging to 3rd–1st century BCE. Prior to the XES study, measurements using Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM‐EDS) revealed that the coins were made of highly concentrated gold (Au) alloy with trace amounts of bismuth (Bi) and, in one case, osmium (Os) and iridium (Ir). Os and Ir together with Pt and other components belong to the Platinum Group Elements (PGE). They form inclusions in ancient gold alloys and their presence is significant in provenance studies since they indicate the use of alluvial gold. Detection of platinum trace elements in a golden matrix is not possible using energy dispersive x‐ray emission techniques (SEM‐EDS, ED‐XRF, or PIXE) because of the limited energy resolution of the Si detectors. A way to overcome this problem is by using a high‐resolution wavelength dispersive x‐ray emission technique. For this purpose, we built a crystal spectrometer in Von‐Hamos geometry. In the framework of this study three samples/coins have been measured, and the presence of Pt was verified in one of them. The limitations of our spectrometer are critically evaluated and ways to optimize the performance of the spectrometer are discussed.

An upgraded version of the water-jet plasma X-ray source suitable for handling the 100 W power of the driving 1 kHz optical parametric chirped-pulse amplification (OPCPA) L1 Allegra laser system has been installed and commissioned at ELI Beamlines. Hard X-ray generation with the L1 Allegra laser is demonstrated for the first time., ELI Beamlines is a rapidly progressing pillar of the pan-European Extreme Light Infrastructure (ELI) project focusing on the development and deployment of science driven by high-power lasers for user operations. This work reports the results of a commissioning run of a water-jet plasma X-ray source driven by the L1 Allegra laser, outlining the current capabilities and future potential of the system. The L1 Allegra is one of the lasers developed in-house at ELI Beamlines, designed to be able to reach a pulse energy of 100 mJ at a 1 kHz repetition rate with excellent beam properties. The water-jet plasma X-ray source driven by this laser opens opportunities for new pump–probe experiments with sub-picosecond temporal resolution and inherent synchronization between pump and probe pulses.

Scientific data 3, 160064 -(2016). doi:10.1038/sdata.2016.64, Single particle diffractive imaging data from Rice Dwarf Virus (RDV) were recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). RDV was chosen as it is a well-characterized model system, useful for proof-of-principle experiments, system optimization and algorithm development. RDV, an icosahedral virus of about 70 nm in diameter, was aerosolized and injected into the approximately 0.1 μm diameter focused hard X-ray beam at the CXI instrument of LCLS. Diffraction patterns from RDV with signal to 5.9 Ångström were recorded. The diffraction data are available through the Coherent X-ray Imaging Data Bank (CXIDB) as a resource for algorithm development, the contents of which are described here., Published by Nature Publ. Group, London

Time-resolved structural investigations of crystallization of water in lipid/protein/salt mesophases at cryogenic temperatures are significant for comprehension of ice nanocrystal nucleation kinetics in lipid membranous systems and can lead to a better understanding of how to experimentally retard the ice formation that obstructs the protein crystal structure determination. Here, we present a time-resolved synchrotron microfocus X-ray diffraction (TR-XRD) study based on ∼40,000 frames that revealed the dynamics of water-to-ice crystallization in a lipid/protein/salt mesophase subjected to cryostream cooling at 100 K. The monoolein/hemoglobin/salt/water system was chosen as a model composition related to protein-loaded lipid cubic phases (LCP) broadly used for the crystallization of proteins. Under confinement in the nanoscale geometry, metastable short-living cubic ice (I

Flavin mononucleotide (FMN) belongs to the large family of flavins, ubiquitous yellow-coloured biological chromophores that contain an isoalloxazine ring system. As a cofactor in flavoproteins, it is found in various enzymes and photosensory receptors, like those featuring the light-oxygen-voltage (LOV) domain. The photocycle of FMN is triggered by blue light and proceeds via a cascade of intermediate states. In this work, we have studied isolated FMN in an aqueous solution in order to elucidate the intrinsic electronic and vibrational changes of the chromophore upon excitation. The ultrafast transitions of excited FMN were monitored through the joint use of femtosecond stimulated Raman spectroscopy (FSRS) and transient absorption spectroscopy encompassing a time window between 0 ps and 6 ns with 50 fs time resolution. Global analysis of the obtained transient visible absorption and transient Raman spectra in combination with extensive quantum chemistry calculations identified unambiguously the singlet and triplet FMN populations and addressed solvent dynamics effects. The good agreement between the experimental and theoretical spectra facilitated the assignment of electronic transitions and vibrations. Our results represent the first steps towards more complex experiments aimed at tracking structural changes of FMN embedded in light-inducible proteins upon photoexcitation.

This paper reports on improved techniques to create and characterize nanometre-sized droplets from dilute aqueous solutions by using a gas dynamic virtual nozzle (GDVN). It describes a method to measure the size distribution of uncharged droplets, using an environmental scanning electron microscope, and provides theoretical models for the droplet sizes created. The results show that droplet sizes can be tuned by adjusting the gas and liquid flow rates in the GDVN, and at the lowest liquid flow rates, the size of the water droplets peaks at about 120 nm. This droplet size is similar to droplet sizes produced by electrospray ionization but requires neither electrolytes nor charging of the solution. The results presented here identify a new operational regime for GDVNs and show that predictable droplet sizes, comparable to those obtained by electrospray ionization, can be produced by purely mechanical means in GDVNs.

Three main paths have been selected within the ELI Beamlines research program for transforming driving laser pulses into brilliant beams of 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 user community. The employment of these beamlines has a well-defined balance between fundamental science and applications in different fields of science and technology. Besides those beamlines, a plasma betatron radiation source driven by the PW-class HAPLS laser system is being commissioned in the plasma physics platform to serve as a unique diagnostic tool for dense plasma and warm dense matter probing.

The dielectric function of Ge measured with static and time-resolved spectroscopic ellipsometry is analyzed using linear filtering techniques to investigate the temperature dependence of the direct band gap, as well as the temporal evolvement of critical points obtained from femtosecond pumpprobe ellipsometry measurements.

We present a setup for time-resolved spectroscopic ellipsometry in a pump–probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer–sample–compensator–analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump–probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV–3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues. Funding: project "Advanced research using high intensity laser produced photons and particles" (ADONIS) from the European Regional Development Fund [CZ.02.1.01/0.0/0.0/16_019/0000789]; project "Structural dynamics of biomolecular systems" (ELIBIO) from the Europea

We report on the status of a users' end-station, MAC: a Multipurpose station for Atomic, molecular and optical sciences and Coherent diffractive imaging, designed for studies of structure and dynamics of matter in the femtosecond time-domain. MAC is located in the E1 experimental hall on the high harmonic generation (HHG) beamline of the ELI Beamlines facility. The extreme ultraviolet beam from the HHG beamline can be used at the MAC end-station together with a synchronized pump beam (which will cover the NIR/Vis/UV or THz range) for time-resolved experiments on different samples. Sample delivery systems at the MAC end-station include a molecular beam, a source for pure or doped clusters, ultrathin cylindrical or flat liquid jets, and focused beams of substrate-free nanoparticles produced by an electrospray or a gas dynamic virtual nozzle combined with an aerodynamic lens stack. We further present the available detectors: electron/ion time-of-flight and velocity map imaging spectrometers and an X-ray camera, and discuss future upgrades: a magnetic bottle electron spectrometer, production of doped nanodroplets and the planned developments of beam capabilities at the MAC end-station., Comment: 14 pages, 13 figures. This is a preprint of an article published in The European Physical Journal Special Topics, 2021

International audience; Time-resolved in-house macromolecular crystallography is primarily limited by the capabilities of the in-house X-ray sources. These sources can only provide a time-averaged structure of the macromolecules. A significant effort has been made in the development of in-house laserdriven ultrafast X-ray sources, with one of the goals as realizing the visualization of the structural dynamics of macromolecules at a very short timescale within the laboratory-scale infrastructure. Most of such in-house ultrafast X-ray sources are operated at high repetition rates and usually deliver very low flux. Therefore, the necessity of a detector that can operate at the repetition rate of the laser and perform extremely well under low flux conditions is essential. Here, we present experimental results demonstrating the usability of the hybrid-pixel detectors, such as Eiger X 1M, and provide experimental proof that they can be successfully operated to collect macromolecular crystallographic data up to a detector frame rate of 3 kHz from synchrotron sources. Our results also show that the data reduction and structural analysis are successful at such high frame rates and fluxes as low as 10 8 photons/sec, which is comparable to the values expected from a typical laserdriven X-ray source.

Communications Physics 3(1), 97 (2020). doi:10.1038/s42005-020-0362-y, The emergence of high repetition-rate X-ray free-electron lasers (XFELs) powered by superconducting accelerator technology enables the measurement of significantly more experimental data per day than was previously possible. The European XFEL is expected to provide 27,000 pulses per second, over two orders of magnitude more than any other XFEL. The increased pulse rate is a key enabling factor for single-particle X-ray diffractive imaging, which relies on averaging the weak diffraction signal from single biological particles. Taking full advantage of this new capability requires that all experimental steps, from sample preparation and delivery to the acquisition of diffraction patterns, are compatible with the increased pulse repetition rate. Here, we show that single-particle imaging can be performed using X-ray pulses at megahertz repetition rates. The results obtained pave the way towards exploiting high repetition-rate X-ray free-electron lasers for single-particle imaging at their full repetition rate., Published by Springer Nature, London

We report results from visible and UV Raman spectroscopy studies of the phonon spectra of a polycrystalline sample of the prototypical perovskite type oxide BaZrO

A fast X-ray focusing polycapillary alignment method was implemented and tested using a compact short-pulse laser-driven broadband X-ray source., A new modification of a table-top laser-driven water-jet plasma X-ray source has been successfully implemented and commissioned at the Extreme Light Infrastructure (ELI) Beamlines user facility. In order to preserve the broadband nature of the source for spectroscopic experiments, a polycapillary lens was initially chosen as the focusing element. Generally, polycapillary X-ray optics have a narrow photon acceptance angle and small field of view, making alignment complicated and time-consuming. This contribution demonstrates a straightforward, reliable and reproducible procedure for aligning polycapillary focusing optics with broadband X-rays. The method involves a pre-alignment step where two X-ray slits are mounted orthogonally on opposite sides of a 3D-printed cylindrical polycapillary holder. This helps to precisely determine the optical axis of the X-ray beam. Subsequent mounting of the polycapillary in the pre-aligned holder with the slits removed allowed for immediate transmission of the X-ray photons through the optics and has provided a good starting point for fine alignment.

Diffraction experiments using high energy X-rays are used to determine molecular structures at high resolution, and with new free electron lasers diffraction experiments on non-crystalline samples are becoming achievable. The authors present a statistical method to identify hit events in flash X-ray imaging experiments of macromolecular complex and demonstrate it on RNA polymerase data.

Rayleigh-scattering microscopy permits tracking and sizing of aerosolized particles down to 40 nm in diameter. It lays the foundation for lab-based injector development and online injection diagnostics for X-ray free-electron laser (XFEL) research., Ultra-bright femtosecond X-ray pulses generated by X-ray free-electron lasers (XFELs) can be used to image high-resolution structures without the need for crystallization. For this approach, aerosol injection has been a successful method to deliver 70–2000 nm particles into the XFEL beam efficiently and at low noise. Improving the technique of aerosol sample delivery and extending it to single proteins necessitates quantitative aerosol diagnostics. Here a lab-based technique is introduced for Rayleigh-scattering microscopy allowing us to track and size aerosolized particles down to 40 nm in diameter as they exit the injector. This technique was used to characterize the ‘Uppsala injector’, which is a pioneering and frequently used aerosol sample injector for XFEL single-particle imaging. The particle-beam focus, particle velocities, particle density and injection yield were measured at different operating conditions. It is also shown how high particle densities and good injection yields can be reached for large particles (100–500 nm). It is found that with decreasing particle size, particle densities and injection yields deteriorate, indicating the need for different injection strategies to extend XFEL imaging to smaller targets, such as single proteins. This work demonstrates the power of Rayleigh-scattering microscopy for studying focused aerosol beams quantitatively. It lays the foundation for lab-based injector development and online injection diagnostics for XFEL research. In the future, the technique may also find application in other fields that employ focused aerosol beams, such as mass spectrometry, particle deposition, fuel injection and three-dimensional printing techniques.

Nature chemistry 10, 355 – 362 (2018). doi:10.1038/nchem.2916, The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex—with a specifically designed constraining ligand geometry—that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine–quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet–visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range., Published by Nature Publishing Group, London

A state of the art ellipsometer for user operations is being implemented at ELI Beamlines in Prague, Czech Republic. It combines three of the most promising and exotic forms of ellipsometry: VUV, pump-probe and magneto-optical ellipsometry. This new ellipsometer covers a spectral operational range from the NIR up to the VUV, with high through-put between 1 and 40 eV. The ellipsometer also allows measurements of magneto-optical spectra with a 1 kHz switchable magnetic field of up to 1.5 T across the sample combining ellipsometry and Kerr spectroscopy measurements in an unprecedented spectral range. This form of generalized ellipsometry enables users to address diagonal and off-diagonal components of the dielectric tensor within one measurement. Pump-probe measurements enable users to study the dynamic behaviour of the dielectric tensor in order to resolve the time-domain phenomena in the femto to 100 ns range.

We report on the results of the recent experiments of the XUV ELIps reflection and ellipsometry station at ELI Beamlines. Using the High Harmonic Generation source and a 1 kHz in-house developed laser, experiments in known samples such as GaN, STO and SiC were done and will be discussed.

In this paper, the authors present the characterization experiments of a 20 fs vacuum ultraviolet beam from a high harmonic generation source. The beam hits a silicon sample and passes a triple reflection gold polarizer located inside an ultrahigh vacuum chamber. The polarizer’s Malus curve was obtained; the total acquisition time for each point of the curve was 30 s. This aims to be the first vacuum ultraviolet time-resolved user station dedicated to ellipsometry. The high harmonic beam is generated by a 12 mJ, 1 kHz, 20 fs, in-house-developed laser and detected by a back-illuminated charge-coupled device.In this paper, the authors present the characterization experiments of a 20 fs vacuum ultraviolet beam from a high harmonic generation source. The beam hits a silicon sample and passes a triple reflection gold polarizer located inside an ultrahigh vacuum chamber. The polarizer’s Malus curve was obtained; the total acquisition time for each point of the curve was 30 s. This aims to be the first vacuum ultraviolet time-resolved user station dedicated to ellipsometry. The high harmonic beam is generated by a 12 mJ, 1 kHz, 20 fs, in-house-developed laser and detected by a back-illuminated charge-coupled device.

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.

Optics express 28(14), 20686 - (2020). doi:10.1364/OE.393547, The THz-field-driven streak camera has proven to be a powerful diagnostic-technique that enables the shot-to-shot characterization of the duration and the arrival time jitter of free electron laser (FEL) pulses. Here we investigate the performance of three computational approaches capable to determine the duration of FEL pulses with complex temporal structures from single-shot measurements of up to three simultaneously recorded spectra. We use numerically simulated FEL pulses in order to validate the accuracy of the pulse length retrieval in average as well as in a single-shot mode. We discuss requirements for the THz field strength in order to achieve reliable results and compare our numerical study with the analysis of experimental data that were obtained at the FEL in Hamburg - FLASH., Published by Soc., Washington, DC

We present latest progress and experimental capabilities of user-oriented XUV beamline based on high harmonic generation (HHG). The focal length of the HHG was recently extended to 5 meters, upscaling the overall XUV photon flux.

For polarization-resolved reflection experiments such as ellipsometry, not only is high reflectivity in a wide spectral range required for mirrors but also the quality of their polarization response is important. Furthermore, for VUV ellipsometry, optimal angles of incidence at the sample are between \(45^\circ \) and \(60^{\circ }\) with respect to the surface normal. In the best case, a setup should even allow variable angles. This requires reflective optics working at non-grazing incidence. In this theoretical study, a selection of potentially relevant materials and mirror designs for broadband use in the VUV is investigated. Based on the available tabulated databases of optical constants, we performed transfer-matrix calculations to obtain reflectance as well as polarization-response spectra in the desired VUV range up to 50 eV. From the variety of materials, we discuss metals that are otherwise commonly used at grazing incidence, Si, SiC, and as representatives for coating layers MgF\(_2\), SiO\(_2\), and Al\(_2\)O\(_3\). While SiC is most universal, Si with only native oxide layer performs well especially below 25 eV. Aluminum has good properties but oxide layers are very detrimental, as protective coatings are in general.

Electron diffraction experiments on crystals of membrane proteins grown in lipidic mesophases have not been possible owing to a thick layer of viscous crystallization medium around the crystals. Here it is shown that focused ion beam milling at cryogenic temperatures (cryo-FIB milling) can remove the viscous layer, and high-quality electron diffraction on a FIB-milled lamella of a bacteriorhodopsin 3D crystal is demonstrated., Electron crystallography of sub-micrometre-sized 3D protein crystals has emerged recently as a valuable field of structural biology. In meso crystallization methods, utilizing lipidic mesophases, particularly lipidic cubic phases (LCPs), can produce high-quality 3D crystals of membrane proteins (MPs). A major step towards realizing 3D electron crystallography of MP crystals, grown in meso, is to demonstrate electron diffraction from such crystals. The first task is to remove the viscous and sticky lipidic matrix that surrounds the crystals without damaging the crystals. Additionally, the crystals have to be thin enough to let electrons traverse them without significant multiple scattering. In the present work, the concept that focused ion beam milling at cryogenic temperatures (cryo-FIB milling) can be used to remove excess host lipidic mesophase matrix is experimentally verified, and then the crystals are thinned to a thickness suitable for electron diffraction. In this study, bacteriorhodopsin (BR) crystals grown in a lipidic cubic mesophase of monoolein were used as a model system. LCP from a part of a hexagon-shaped plate-like BR crystal (∼10 µm in thickness and ∼70 µm in the longest dimension), which was flash-frozen in liquid nitro­gen, was milled away with a gallium FIB under cryogenic conditions, and a part of the crystal itself was thinned into a ∼210 nm-thick lamella with the ion beam. The frozen sample was then transferred into an electron cryo-microscope, and a nanovolume of ∼1400 × 1400 × 210 nm of the BR lamella was exposed to 200 kV electrons at a fluence of ∼0.06 e Å−2. The resulting electron diffraction peaks were detected beyond 2.7 Å resolution (with an average peak height to background ratio of >2) by a CMOS-based Ceta 16M camera. The results demonstrate that cryo-FIB milling produces high-quality lamellae from crystals grown in lipidic mesophases and pave the way for 3D electron crystallography on crystals grown or embedded in highly viscous media.

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.

Facilitating the very short and intense pulses from an X-ray laser for the purpose of imaging small bioparticles carries the potential for structure determination at atomic resolution without the need for crystallization. In this study, experimental strategies for this idea are explored based on data collected at the Linac Coherent Light Source from 40 nm virus particles injected into a hard X-ray beam., This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of ∼40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from ∼35 to ∼300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 × 1012 photons per µm2 per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.

We report results from visible and UV Raman spectroscopy studies of the phonon spectra of a polycrystalline sample of the prototypical perovskite type oxide BaZrO3 and a 500 nm thick film of its Y-doped, proton conducting, counterpart BaZr0.8Y0.2O2.9. Analysis of the Raman spectra measured using different excitation energies (between 3.44 eV and 5.17 eV) reveals the activation of strong resonance Raman effects involving all lattice vibrational modes. Specifically, two characteristic energies were identified for BaZrO3, one around 5 eV and one at higher energy, respectively, and one for BaZr0.8Y0.2O2.9, above 5 eV. Apart from the large difference in spectral intensity between the non-resonant and resonant conditions, the spectra are overall similar to each other, suggesting that the vibrational spectra of the perovskites are stable when investigated using an UV laser as excitation source. These results encourage further use of UV Raman spectroscopy as a novel approach for the study of lattice vibrational dynamics and local structure in proton conducting perovskites, and open up for, e.g., time-resolved experiments on thin films targeted at understanding the role of lattice vibrations in proton transport in these kinds of materials.

Aerosol nanoparticle injectors are fundamentally important for experiments where container-free sample handling is needed to study isolated nanoparticles. The injector consists of a nebuliser, a differential pumping unit, and an aerodynamic lens to create and deliver a focused particle beam to the interaction point inside a vacuum chamber. The tightest focus of the particle beam is close to the injector tip. The density of the focusing carrier gas is high at this point. We show here how this gas interacts with a near infrared laser pulse (800 nm wavelength, 120 fs pulse duration) at intensities approaching 1016 Wcm−2. We observe acceleration of gas ions to kinetic energies of 100s eV and study their energies as a function of the carrier gas density. Our results indicate that field ionisation by the intense near-infrared laser pulse opens up a plasma channel behind the laser pulse. The observations can be understood in terms of a Coulomb explosion of the created underdense plasma channel. The results can be used to estimate gas background in experiments with the injector and they open up opportunities for a new class of studies on electron and ion dynamics in nanoparticles surrounded by a low-density gas.