| 1. |
- Appi, E., et al.
(author)
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Two phase-matching regimes in high-order harmonic generation
- 2023
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In: Optics Express. - 1094-4087. ; 31:20, s. 31687-31697
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Journal article (peer-reviewed)abstract
- High-order harmonic generation (HHG) provides scalable sources of coherent extreme ultraviolet radiation with pulse duration down to the attosecond time scale. Efficient HHG requires the constructive interplay between microscopic and macroscopic effects in the generation volume, which can be achieved over a large range of experimental parameters from the driving field properties to those of the generating medium. Here, we present a systematic study of the harmonic yield as a function of gas pressure and medium length. Two regimes for optimum yield are identified, supporting the predictions of a recently proposed analytical model. Our observations are independent on the focusing geometry and, to a large extent, on the pulse duration and laser intensity, providing a versatile approach to HHG optimization.
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| 2. |
- Laurell, Hugo, et al.
(author)
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Measuring the quantum state of photoelectrons
- 2023
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Journal article (other academic/artistic)abstract
- A photoelectron, emitted due to the absorption of light quanta as described by the photoelectric effect, is often characterized experimentally by a classical quantity, its momentum. However, since the photoelectron is a quantum object, its rigorous characterization requires the reconstruction of the complete quantum state, the photoelectron's density matrix. Here, we use quantum state tomography to fully characterize photoelectrons emitted from helium and argon atoms upon absorption of ultrashort, extreme ultraviolet light pulses. While in helium we measure a pure photoelectronic state, in argon, spin-orbit interaction induces entanglement between the ion and the photoelectron, leading to a reduced purity of the photoelectron state. Our work shows how state tomography gives new insights into the fundamental quantum aspects of light-induced electronic processes in matter, bridging the fields of photoelectron spectroscopy and quantum information, and offering new spectroscopic possibilities for quantum technology.
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| 3. |
- Love, David C., et al.
(author)
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Emerging COVID-19 impacts, responses, and lessons for building resilience in the seafood system
- 2021
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In: Global food security. - : Elsevier BV. - 2211-9124. ; 28
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Journal article (peer-reviewed)abstract
- The COVID-19 pandemic and subsequent lockdowns are creating health and economic crises that threaten food and nutrition security. The seafood sector provides important sources of nutrition and employment, especially in low-income countries, and is highly globalized allowing shocks to propagate. We studied COVID-19-related disruptions, impacts, and responses to the seafood sector from January through May 2020, using a food system resilience ‘action cycle’ framework as a guide. We find that some supply chains, market segments, companies, small-scale actors and civil society have shown initial signs of greater resilience than others. COVID-19 has also highlighted the vulnerability of certain groups working in- or dependent on the seafood sector. We discuss early coping and adaptive responses combined with lessons from past shocks that could be considered when building resilience in the sector. We end with strategic research needs to support learning from COVID-19 impacts and responses.
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| 4. |
- Luo, Sizuo, et al.
(author)
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Ultra-stable and versatile high-energy resolution setup for attosecond photoelectron spectroscopy
- 2023
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In: Advances in Physics: X. - 2374-6149. ; 8:1
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Research review (peer-reviewed)abstract
- Attosecond photoelectron spectroscopy has opened up for studying light–matter interaction on ultrafast time scales. It is often performed with interferometric experimental setups that require outstanding stability. We demonstrate and characterize in detail an actively stabilized, versatile, high spectral resolution attosecond beamline based on a Mach-Zehnder interferometer. The active stabilization keeps the interferometer ultra-stable for several hours with an RMS stability of 13 as and a total pump-probe delay scanning range of (Formula presented.) fs. A tunable femtosecond laser source to drive high-order harmonic generation allows for precisely addressing atomic and molecular resonances. Furthermore, the interferometer includes a spectral shaper in 4f-geometry in the probe arm as well as a tunable bandpass filter in the pump arm, which offer additional high flexibility in terms of tunability as well as narrowband or polychromatic probe pulses. We demonstrate the capabilities of the beamline via experiments using several variants of the RABBIT (reconstruction of attosecond beating by two photon transitions) technique. In this setup, the temporal-spectral resolution of photoelectron spectroscopy can reach a new level of accuracy and precision.
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| 5. |
- Mayer, Ludovic, et al.
(author)
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Widespread Pesticide Distribution in the European Atmosphere Questions their Degradability in Air
- 2024
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In: Environmental Science and Technology. - 0013-936X. ; 58:7, s. 3342-3352
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Journal article (peer-reviewed)abstract
- Risk assessment of pesticide impacts on remote ecosystems makes use of model-estimated degradation in air. Recent studies suggest these degradation rates to be overestimated, questioning current pesticide regulation. Here, we investigated the concentrations of 76 pesticides in Europe at 29 rural, coastal, mountain, and polar sites during the agricultural application season. Overall, 58 pesticides were observed in the European atmosphere. Low spatial variation of 7 pesticides suggests continental-scale atmospheric dispersal. Based on concentrations in free tropospheric air and at Arctic sites, 22 pesticides were identified to be prone to long-range atmospheric transport, which included 15 substances approved for agricultural use in Europe and 7 banned ones. Comparison between concentrations at remote sites and those found at pesticide source areas suggests long atmospheric lifetimes of atrazine, cyprodinil, spiroxamine, tebuconazole, terbuthylazine, and thiacloprid. In general, our findings suggest that atmospheric transport and persistence of pesticides have been underestimated and that their risk assessment needs to be improved.
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| 6. |
- Plach, Marius, et al.
(author)
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Spatial Aberrations in High-Order Harmonic Generation
- 2024
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In: Ultrafast Science. - 2097-0331. ; 4
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Journal article (peer-reviewed)abstract
- We investigate the spatial characteristics of high-order harmonic radiation generated in argon and observe cross-like patterns in the far field. An analytical model describing harmonics from an astigmatic driving beam reveals that these patterns result from the order and generation position-dependent divergence of harmonics. Even small amounts of driving field astigmatism may result in cross-like patterns, coming from the superposition of individual harmonics with spatial profiles elongated in different directions. By correcting the aberrations using a deformable mirror, we show that fine-tuning the driving wavefront is essential for optimal spatial quality of the harmonics.
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| 7. |
- Santi, I., et al.
(author)
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European marine omics biodiversity observation network: a strategic outline for the implementation of omics approaches in ocean observation
- 2023
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In: Frontiers in Marine Science. ; 10
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Journal article (peer-reviewed)abstract
- Marine ecosystems, ranging from coastal seas and wetlands to the open ocean, accommodate a wealth of biological diversity from small microorganisms to large mammals. This biodiversity and its associated ecosystem function occurs across complex spatial and temporal scales and is not yet fully understood. Given the wide range of external pressures on the marine environment, this knowledge is crucial for enabling effective conservation measures and defining the limits of sustainable use. The development and application of omics-based approaches to biodiversity research has helped overcome hurdles, such as allowing the previously hidden community of microbial life to be identified, thereby enabling a holistic view of an entire ecosystem's biodiversity and functioning. The potential of omics-based approaches for marine ecosystems observation is enormous and their added value to ecosystem monitoring, management, and conservation is widely acknowledged. Despite these encouraging prospects, most omics-based studies are short-termed and typically cover only small spatial scales which therefore fail to include the full spatio-temporal complexity and dynamics of the system. To date, few attempts have been made to establish standardised, coordinated, broad scaled, and long-term omics observation networks. Here we outline the creation of an omics-based marine observation network at the European scale, the European Marine Omics Biodiversity Observation Network (EMO BON). We illustrate how linking multiple existing individual observation efforts increases the observational power in large-scale assessments of status and change in biodiversity in the oceans. Such large-scale observation efforts have the added value of cross-border cooperation, are characterised by shared costs through economies of scale, and produce structured, comparable data. The key components required to compile reference environmental datasets and how these should be linked are major challenges that we address.
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