| 1. |
- Allaria, E., et al.
(författare)
-
Highly coherent and stable pulses from the FERMI seeded free-electron laser in the extreme ultraviolet
- 2012
-
Ingår i: Nature Photonics. - 1749-4885. ; 6:10, s. 699-704
-
Tidskriftsartikel (refereegranskat)abstract
- Free-electron lasers (FELs) are promising devices for generating light with laser-like properties in the extreme ultraviolet and X-ray spectral regions. Recently, FELs based on the self-amplified spontaneous emission (SASE) mechanism have allowed major breakthroughs in diffraction and spectroscopy applications, despite the relatively large shot-to-shot intensity and photon-energy fluctuations and the limited longitudinal coherence inherent in the SASE mechanism. Here, we report results on the initial performance of the FERMI seeded FEL, based on the high-gain harmonic generation configuration, in which an external laser is used to initiate the emission process. Emission from the FERMI FEL-1 source occurs in the form of pulses carrying energy of several tens of microjoules per pulse and tunable throughout the 65 to 20 nm wavelength range, with unprecedented shot-to-shot wavelength stability, low-intensity fluctuations, close to transform-limited bandwidth, transverse and longitudinal coherence and full control of polarization.
|
|
| 2. |
- Mirian, N. S., et al.
(författare)
-
Generation and measurement of intense few-femtosecond superradiant extreme-ultraviolet free-electron laser pulses
- 2021
-
Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 15, s. 523-529
-
Tidskriftsartikel (refereegranskat)abstract
- Free-electron lasers producing ultrashort pulses with high peak power promise to extend ultrafast non-linear spectroscopic techniques into the extreme-ultraviolet-X-ray regime. Key aspects are the synchronization between pump and probe, and the control of the pulse properties (duration, intensity and coherence). Externally seeded free-electron lasers produce coherent pulses that can be synchronized with femtosecond accuracy. An important goal is to shorten the pulse duration, but the simple approach of shortening the seed is not sufficient because of the finite-gain bandwidth of the conversion process. An alternative is the amplification of a soliton in a multistage, superradiant cascade: here, we demonstrate the generation of few-femtosecond extreme-ultraviolet pulses, whose duration we measure by autocorrelation. We achieve pulses four times shorter, and with a higher peak power, than in the standard high-gain harmonic generation mode and we prove that the pulse duration matches the Fourier transform limit of the spectral intensity distribution. By amplifying a soliton in a multistage cascade, few-femtosecond extreme-ultraviolet free-electron laser pulses are achieved.
|
|
| 3. |
|
|
| 4. |
- Garofalo, Danilo F. Trovo, et al.
(författare)
-
Land-use change CO2 emissions associated with agricultural products at municipal level in Brazil
- 2022
-
Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526 .- 1879-1786. ; 364
-
Tidskriftsartikel (refereegranskat)abstract
- Land-use change (LUC) accounted for approximately 66% of CO2 emissions in Brazil in 2020, with significant implications for carbon footprint of Brazilian agricultural products. Accurate LUC estimates associated with agriculture are critical to carbon footprint (CF) and life cycle assessment (LCA) studies and derived measures towards low-carbon supply chains. The aim of the study was to provide direct LUC (dLUC) estimates of CO2 emissions associated with a comprehensive set of agricultural products in Brazil at municipal-level and based on spatially-explicit land conversion data, appropriate for CF and LCA studies. The effect of different dLUC modeling choices on the results are also presented. The modeling followed IPCC guidelines and improved the BRLUC method. MapBiomas spatially-explicit data, municipality-level statistics, regionalized carbon stocks and a shared responsibility approach were combined to obtain dLUC emission rates for 64 crops, plus forestry and planted pastures, in the 5,570 Brazilian municipalities, as well as at state and national levels. It will be open access at www.embrapa.br. The most recent version led to an estimated 911 Mtons of CO2 associated with agriculture in 2019, 81% of that associated with planted pastures. National level dLUC emission rates for corn, pastures, soybean and sugarcane were estimated as 2.0, 4.1, 2.3 and 0.3 tCO(2).ha(-1).yr(-1), respectively. The dLUC emissions are highly heterogeneous across the country and land uses, ranging from positive to negative. In general, they were higher in the Amazon biome, due to deforestation, and lower in Eastern Brazil, where agricultural areas are more consolidated. The resulting data is more consistent with dLUC rationale, IPCC guidelines and PAS2050 when previous land use is known and is recommended to be used, whenever data at farm level are not available. The study also shows the strong effect of different dLUC modeling choices on results and reinforces recommendations for further mitigation options.
|
|
| 5. |
- Maciel, Vinicius Goncalves, et al.
(författare)
-
Towards a non-ambiguous view of the amortization period for quantifying direct land-use change in LCA
- 2022
-
Ingår i: The International Journal of Life Cycle Assessment. - : Springer Nature. - 0948-3349 .- 1614-7502. ; 27:12, s. 1299-1315
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose To clarify the concept of the amortization period (20-year factor) associated with direct land-use change (dLUC) accounting, discuss its main inconsistencies, and propose improvements. The current practice is to divide (amortize) the estimated emissions associated with dLUC that has occurred over the last 20 years by another 20 years. Both periods are referred ambiguously as "amortization period." Issues arise when considering them as a single temporal aspect (TA) that cannot fully represent the complexity of diverse research and policy contexts. Methods First, a systematic review was conducted to understand the 20-year amortization history and concepts and discuss its inconsistencies. Based on the review results, we propose the adoption of two distinct TAs, decomposed from the "amortization period." Then, we performed a sensitivity analysis by estimating carbon emissions due to dLUC in six land uses in Brazil: soybean, maize, sugarcane, pasture, planted forest, and mango. Results and discussion The literature review shows that several strategies have emerged to reduce or avoid adopting the amortization period. However, most of these proposals are based on complex approaches focusing on alternatives associated with the life cycle impact assessment stage. We found that the commonly adopted amortization period has an ambiguous nature that could be explored at the life cycle inventory analysis stage. Thus, we argue that there are two distinct TAs linked to amortization in dLUC: (i) the inventory period adopted to account for land-use changes; and (ii) the period over which carbon emissions are annualized. These temporal aspects were named here the "LUC-inventory period" (IP) and the "LUC-amortization period" (AP), for clarification purposes. The sensitivity analysis showed that different values of IP and AP drastically change the emissions results due to dLUC in Brazil for different crops and land uses. Conclusion We advocate that the "amortization period" should be decomposed into two TAs: "LUC-inventory period" and the "LUC-amortization period." They affect how the carbon debt incurred by expanding agricultural land is accounted for and amortized over a given period-of-time. Therefore, to ensure regulatory compliance, we argued that these proposed TAs should be explicitly defined, based on three possibilities, depending on the goal and context of LCA studies, such as (i) fixed values set in standards and norms; (ii) IPCC's 20-year defaults; and (iii) customized IP and AP values based on the study's specificities.
|
|
| 6. |
|
|
| 7. |
- Pop, Mihai, et al.
(författare)
-
Single-shot transverse coherence in seeded and unseeded free-electron lasers: A comparison
- 2022
-
Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 25:040701
-
Tidskriftsartikel (refereegranskat)abstract
- The advent of x-ray free-electron lasers (FELs) drastically enhanced the capabilities of several analytical techniques, for which the degree of transverse (spatial) coherence of the source is essential. FELs can be operated in self-amplified spontaneous emission (SASE) or seeded configurations, which rely on a qualitatively different initialization of the amplification process leading to light emission. The degree of transverse coherence of SASE and seeded FELs has been characterized in the past, both experimentally and theoretically. However, a direct experimental comparison between the two regimes in similar operating conditions is missing, as well as an accurate study of the sensitivity of transverse coherence to key working parameters. In this paper, we carry out such a comparison, focusing in particular on the evolution of coherence during the light amplification process.
|
|
| 8. |
- Walker, R.P., et al.
(författare)
-
The European UV/VUV storage ring FEL at ELETTRA : First operation and future prospects
- 2001
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 467-468, s. 34-37
-
Tidskriftsartikel (refereegranskat)abstract
- A European project to develop the first storage ring free-electron laser on a third-generation synchrotron radiation facility is presented, including a description of the main features, initial performance at 350 and 220 nm and future prospects.
|
|
