| 1. |
- Veyrinas, K., et al.
(författare)
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Chromatic aberrations correction of attosecond high-order harmonic beams by flat-top spatial shaping of the fundamental beam
- 2023
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- Attosecond pulses created by high-order harmonic generation in gases often exhibit strong chromatic aberrations, arising from the broad bandwidth and wavelength-dependent nonlinear light-matter interaction. When the driving laser intensity varies spatially, as for Gaussian driving beams, the apparent source position of the harmonics differs significantly from one order to the next, thus affecting the achievable intensity and duration of the attosecond pulses when they are focused on a target. We show that these chromatic aberrations can be reduced by spatially shaping the fundamental beam to generate high-order harmonics with a driver having a flat-top profile inside the gas medium. By measuring both the intensity profile and wavefront for each harmonic in a plane, we access the extreme ultra-violet (XUV) beam properties and investigate these properties near focus. We observe that controlling chromatic aberrations by flat-top spatial shaping strongly reduces the variation of the XUV spectrum on the beam axis during propagation and, in return, the longitudinal sensitivity of both the temporal profiles and the temporal shifts of the focused attosecond pulses.
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| 2. |
- Veyrinas, K., et al.
(författare)
-
High order harmonic generation with spatially shaped flat top driver to control XUV chromatic aberrations
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - 9798350345995
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Konferensbidrag (refereegranskat)abstract
- The XUV beams generated via high order harmonic generation (HHG) in gases have spatial properties evolving with the harmonic order. It leads to chromatic aberrations when the harmonics are focussed so that, locally, the spectral content can change significantly during propagation [1-3] especially near focus.
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| 3. |
- Tognon, Gianluca, et al.
(författare)
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Development of the Choices 5-Level Criteria to Support Multiple Food System Actions
- 2021
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Ingår i: Nutrients. - : MDPI AG. - 2072-6643. ; 13:12
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Tidskriftsartikel (refereegranskat)abstract
- In 2008, the Choices International Foundation developed its logo criteria, identifying best-in-class food products. More advanced, global and graded nutrient profiling systems (NPSs) are needed to substantiate different national nutrition policies. The objective of this work was to extend Choices NPS to identify five levels of the healthiness of food products, so that the Choices NPS can also be used to support other nutrition policies, next to front-of-pack labelling. Based on the same principles as the previous logo criteria, four sets of threshold criteria were determined using a combination of compliance levels, calculated from a large international food group-specific database, the Choices logo criteria, and WHO-NPSs developed to restrict marketing to children. Validation consisted of a comparison with indicator foods from food-based dietary guidelines from various countries. Some thresholds were adjusted after the validation, e.g., because intermediate thresholds were too lenient. This resulted in a new international NPS that can be applied to different contexts and to support a variety of health policies, to prevent both undernutrition and obesity. It can efficiently evaluate mixed food products and represents a flexible tool, applicable in various settings and populations.
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