CAMP@FLASH: an end-station for imaging, electron- and ion-spectroscopy, and pump–probe experiments at the FLASH free-electron laser

The non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump–probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, along with large-area single-photon-counting pnCCD X-ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end-station are presented, as well as results from its commissioning

Atomic, Molecular and Cluster Science with the Reaction Microscope Endstation at FLASH2

The reaction microscope (REMI) endstation for atomic and molecular science at the free-electron laser FLASH2 at DESY in Hamburg is presented together with a brief overview of results recently obtained. The REMI allows coincident detection of electrons and ions that emerge from atomic or molecular fragmentation reactions in the focus of the extreme-ultraviolet (XUV) free-electron laser (FEL) beam. A large variety of target species ranging from atoms and molecules to small clusters can be injected with a supersonic gas-jet into the FEL focus. Their ionization and fragmentation dynamics can be studied either under single pulse conditions, or for double pulses as a function of their time delay by means of FEL-pump–FEL-probe schemes and also in combination with a femtosecond infrared (IR) laser. In a recent upgrade, the endstation was further extended by a light source based on high harmonic generation (HHG), which is now available for upcoming FEL/HHG pump–probe experiments

Symmetry-breaking dynamics of a photoionized carbon dioxide dimer

Abstract Photoionization can initiate structural reorganization of molecular matter and drive formation of new chemical bonds. Here, we used time-resolved extreme ultraviolet (EUV) pump – EUV probe Coulomb explosion imaging of carbon dioxide dimer ion $${\left({{{\rm{C}}}}{{{{\rm{O}}}}}_{2}\right)}_{2}^{+}$$ C O 2 2 + dynamics, that combined with ab initio molecular dynamics simulations, revealed unexpected asymmetric structural rearrangement. We show that ionization by the pump pulse induces rearrangement from the slipped-parallel (C2h) geometry of the neutral $${{{\rm{C}}}}{{{{\rm{O}}}}}_{2}$$ C O 2 dimer towards a T-shaped (C2v) structure on the ~100 fs timescale, although the most stable slipped-parallel (C2h) structure of the ionic dimer. Moreover, we find that excited states of the ionized $${{{\rm{C}}}}{{{{\rm{O}}}}}_{2}$$ C O 2 dimer can exhibit formation of a $${{{{\rm{CO}}}}}_{3}$$ CO 3 moiety in the $${{{{\rm{C}}}}}_{2}{{{{\rm{O}}}}}_{4}^{+}\,$$ C 2 O 4 + complex that can persist even after a suitably time-delayed second photoionization in a metastable $${{{{\rm{C}}}}}_{2}{{{{\rm{O}}}}}_{4}^{2+}$$ C 2 O 4 2 + dication. Our results suggest that charge asymmetry plays an important role in the ionization-induced dynamics in such dimers that are present in $${{{\rm{C}}}}{{{{\rm{O}}}}}_{2}$$ C O 2 rich environments

Direct tracking of ultrafast proton transfer in water dimers

Upon ionization, water forms a highly acidic radical cation H$_2$O$^+$· that undergoes ultrafast proton transfer (PT)—a pivotal step in water radiation chemistry, initiating the production of reactive H$_3$O$^+$, OH radicals, and a (hydrated) electron. Until recently, the time scales, mechanisms, and state-dependent reactivity of ultrafast PT could not be directly traced. Here, we investigate PT in water dimers using time-resolved ion coincidence spectroscopy applying a free-electron laser. An extreme ultraviolet (XUV) pump photon initiates PT, and only dimers that have undergone PT at the instance of the ionizing XUV probe photon result in distinct H$_3$O$^+$ + OH$^+$ pairs. By tracking the delay-dependent yield and kinetic energy release of these ion pairs, we measure a PT time of (55 ± 20) femtoseconds and image the geometrical rearrangement of the dimer cations during and after PT. Our direct measurement shows good agreement with nonadiabatic dynamics simulations for the initial PT and allows us to benchmark nonadiabatic theory

Photoelectron spectroscopy of laser-dressed atomic helium

© 2020 authors. Photoelectron emission from excited states of laser-dressed atomic helium is analyzed with respect to laser intensity-dependent excitation energy shifts and angular distributions. In the two-color exteme ultraviolet (XUV)-infrared (IR) measurement, the XUV photon energy is scanned between 20.4 eV and the ionization threshold at 24.6 eV, revealing electric dipole-forbidden transitions for a temporally overlapping IR pulse (≈1012Wcm-2). The interpretation of the experimental results is supported by numerically solving the time-dependent Schrödinger equation in a single-active-electron approximation

Differential Measurement of Electron Ejection after Two-Photon Two-Electron Excitation of Helium

We report the measurement of the photoelectron angular distribution of two-photon single-ionization near the $2p^2$ $^1D^e$ double-excitation resonance in helium, benchmarking the fundamental nonlinear interaction of two photons with two correlated electrons. This observation is enabled by the unique combination of intense extreme ultraviolet pulses, delivered at the high-repetition-rate free-electron laser in Hamburg (FLASH), ionizing a jet of cryogenically cooled helium atoms in a reaction microscope. The spectral structure of the intense self-amplified spontaneous emission free-electron laser pulses has been resolved on a single-shot level to allow for post selection of pulses, leading to an enhanced spectral resolution, and introducing a new experimental method. The measured angular distribution is directly compared to state-of-the-art theory based on multichannel quantum defect theory and the streamlined $R$-matrix method. These results and experimental methodology open a promising route for exploring fundamental interactions of few photons with few electrons in general

Note on the Construction of Groins at Dingwall, Nova Scotia.

NRC publication: Ye

Evaluation of Four Tools for Environmental Impact Life Cycle Assessment in Sustainable Product Development

Reliable environmental impact life cycle assessment (LCA) is a major striking research area in sustainableproduct development. This paper is to answer “what capabilities and limitations do current LCA tools insustainable product development have?” In this paper four different LCA tools are studied, their capabilitiesand limitations presented and various comparisons are made. In addition, a case study on road pavementsrepresents the importance of comprehensive LCA. The case questions the validity of single environmentalimpact LCA approaches and the reliability of partial LCA. The paper concludes by addressing a number ofconcerns about LCA tools and methods