| 1. |
- Erny, Christian, et al.
(författare)
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Metrology of high-order harmonics for free-electron laser seeding
- 2011
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- We examine the characteristics of high-order harmonics generated with 800 nm, 25 mJ, 160 fs laser pulses in an Ar gas cell with the objective of seeding a free electron laser. We measure the energy per pulse and per harmonic, the energy jitter, the divergence and the position stability of the harmonic beam. We perform ab initio numerical simulations based on integration of the time-dependent Schrodinger equation and of the wave equation within the slowly varying envelope approximation. The results reproduce the experimental measurements to better than a factor of two. The interaction of a frequency comb of harmonic fields with an electron bunch in an undulator is examined with a simple model consisting of calculating the energy modulation owing to the seed-electron interaction. The model indicates that the undulator acts as a spectral filter selecting a given harmonic.
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| 2. |
- Gabrysch, Markus, et al.
(författare)
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XUV-induced transient phase gratings for probing ultra-fast carrier generation and recombination processes in wide-bandgap semiconductors
- 2013
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 525:1-2, s. 59-65
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Tidskriftsartikel (refereegranskat)abstract
- A method for probing the temporal evolution of ultra-fast carrier generation and recombination processes in wide-bandgap semiconductors, e.g. diamond, is described. Two extreme ultraviolet (pump) pulses produced by high-order harmonic generation in Argon gas (with a photon energy of 32 eV) are superimposed on a sample with a small angle between them, inducing periodic changes in the refractive index of the material causing it to act as a transient diffraction grating. A delayed synchronized infrared (probe) pulse gets diffracted on the induced phase grating and is detected in the first diffraction order. By varying the time-delay between pump and probe, the full temporal evolution of the free carrier generation and recombination processes can be resolved. Feasibility calculations and the first steps towards experimental implementation are presented.
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| 3. |
- He, Xinkui, et al.
(författare)
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Interference effects in two-color high-order harmonic generation
- 2010
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 82:3
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Tidskriftsartikel (refereegranskat)abstract
- We study high-order harmonic generation in argon driven by an intense 800 nm laser field and a small fraction of its second harmonic. The intensity and divergence of the emitted even and odd harmonics are strongly modulated as a function of the relative delay between the two fields. We provide a detailed analysis of the underlying interference effects. The interference changes drastically when approaching the cutoff region due to a switch of the dominant trajectory responsible for harmonic generation.
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| 4. |
- He, Xinkui, et al.
(författare)
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Spatial and spectral properties of the high-order harmonic emission in argon for seeding applications
- 2009
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 79:6
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Tidskriftsartikel (refereegranskat)abstract
- We characterize and control the harmonic emission in the spectral and spatial domains in order to define in which conditions the harmonic radiation can be a high-quality seed for soft x-ray and x-ray free-electron lasers. The length of the gas cell, where harmonics are generated, was optimized and the energy per pulse was determined in absolute value with a calibrated x-ray photodiode. The beam spatial profile was measured and, in some conditions, a very collimated beam with a half-angle divergence below 1 mrad could be obtained. We also show that increasing the intensity of the fundamental laser field leads to a considerable broadening of the bandwidth of the harmonic radiation, allowing us to cover a large spectral range. This effect is due to fundamental reshaping leading to an efficient phase matching of both short- and long-trajectory contributions.
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| 5. |
- Rakowski, Rafal, et al.
(författare)
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Characterization and optimization of the laser-produced plasma EUV source at 13.5 nm based on a double-stream Xe/He gas puff target
- 2010
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 101:4, s. 773-789
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Tidskriftsartikel (refereegranskat)abstract
- The paper describes a debris-free, efficient laser-produced plasma source emitting EUV radiation. The source is based on a double-stream Xe/He gas-puff. Its properties and spectroscopic signatures are characterized and discussed. The spatio-spectral features of the EUV emission are investigated. We show a large body of results related to the intensity and brightness of the EUV emission, its spatial, temporal, and angular behavior and the effect of the repetition rate as well. A conversion efficiency of laser energy into EUV in-band energy at 13.5 nm of 0.42% has been gained. The electron temperature and electron density of the source were estimated by means of a novel method using the FLY code. The experimental data and the Hullac code calculations are compared and discussed. The source is well suited for EUV metrology purposes. The potential of the source for application in EUV lithography was earlier demonstrated in the optical characterization of Mo/Si multi-layer mirrors and photo-etching of polymers.
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| 6. |
- Rakowski, Rafal, et al.
(författare)
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Laser-produced plasma EUV source based on tin-rich, thin-layer targets
- 2011
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 102:3, s. 559-567
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a new approach to a laser-produced plasma EUV source based on a tin target is presented. A thin layer of pure tin and composite layers consisting of Sn with Si, SiO and LiF are investigated. The target composed of several thin layers produces less debris than the other targets and provides a conversion efficiency (CE) in the 13.5-nm +/- 1% band at least comparable to the CE for the pure tin slab target. The largest CE was observed for the target composed of a mixture of Sn and LiF, due to the fact that lithium, similarly to tin, is a strong emitter at 13.5 nm.
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| 7. |
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| 8. |
- Rakowski, Tomasz, et al.
(författare)
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Early abciximab administration before transfer for primary percutaneous coronary interventions for ST-elevation myocardial infarction reduces 1-year mortality in patients with high-risk profile. Results from EUROTRANSFER Registry
- 2009
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Ingår i: AMERICAN HEART JOURNAL. - : Elsevier BV. - 0002-8703. ; 158:4, s. 569-575
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Tidskriftsartikel (refereegranskat)abstract
- Background There are conflicting data on the clinical benefit from early administration of abciximab from a large randomized trial and a registry. However, both sources suggest that a benefit may depend on the baseline risk profile of the patients. We evaluated the role of early abciximab administration in patients with ST-segment-elevation myocardial infarction (STEMI) referred for primary percutaneous coronary intervention stratified by the STEMI Thrombolysis In Myocardial Infarction (TIMI) risk score. Methods A total of 1,650 patients were enrolled into the EUROTRANSFER Registry. One thousand eighty-six patients received abciximab (66%). Abciximab was administered early in 727 patients (EA) and late in 359 patients (LA). We used the TIMI risk score for risk stratification. Patients with scores 3 constituted the high-risk group of 616 patients (56.7%), whereas 470 patients formed the low-risk cohort. Factoring in the timing of the abciximab administration resulted in 4 groups of patients who were compared for mortality at 1 year: EA/high-risk (n = 413); LA/high-risk (n = 203); EA/low-risk (n = 3 14); LA/low-risk (n = 156). Baseline difference was accounted for by means of propensity score. Results In high-risk patients, 1-year mortality was significantly lower with early abcximab compared to late administration (8.7% vs 15.8%; odds ratio 0.51, CI 0.31-0.85, P = .01). In multivariable Cox regression analysis, both early abciximab administration and patients risk profile (TIMI score :3) were identified as independent predictors of 1-year mortality. Conclusions Early abciximab administration before transfer for percutaneous coronary intervention in STEMI shows lower mortality at 1-year follow-up. This effect is confined to patients with higher risk profile as defined by TIMI risk score andgt;= 3.
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| 9. |
- Rudawski, Piotr, et al.
(författare)
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A high-flux high-order harmonic source.
- 2013
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 84:7
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Tidskriftsartikel (refereegranskat)abstract
- We develop and implement an experimental strategy for the generation of high-energy high-order harmonics (HHG) in gases for studies of nonlinear processes in the soft x-ray region. We generate high-order harmonics by focusing a high energy Ti:Sapphire laser into a gas cell filled with argon or neon. The energy per pulse is optimized by an automated control of the multiple parameters that influence the generation process. This optimization procedure allows us to obtain energies per pulse and harmonic order as high as 200 nJ in argon and 20 nJ in neon, with good spatial properties, using a loose focusing geometry (f#≈400) and a 20 mm long medium. We also theoretically examine the macroscopic conditions for absorption-limited conversion efficiency and optimization of the HHG pulse energy for high-energy laser systems.
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| 10. |
- Schwenke, Jörg, et al.
(författare)
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Digital in-line holography on amplitude and phase objects prepared with electron beam lithography.
- 2012
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720. ; 247:2, s. 196-201
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and characterization of amplitude and phase samples consisting of well defined Au or Al features formed on ultrathin silicon nitride membranes. The samples were manufactured using electron beam lithography, metallization and a lift-off technique, which allow precise lateral control and thickness of the metal features. The fabricated specimens were evaluated by conventional microscopy, atomic force microscopy and with the digital in-line holography set-up at the Lund Laser Centre. The latter uses high-order harmonic generation as a light source, and is capable of recovering both the shape and phase shifting properties of the samples. We report on the details of the sample production and on the imaging tests with the holography set-up.
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