| 1. |
- Le Guyader, Loïc, et al.
(författare)
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State-resolved ultrafast charge and spin dynamics in [Co/Pd] multilayers
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:3
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Tidskriftsartikel (refereegranskat)abstract
- We use transient absorption spectroscopy with circularly polarized x rays to detect laser-excited hole states below the Fermi level and compare their dynamics with that of unoccupied states above the Fermi level in ferromagnetic [Co/Pd] multilayers. While below the Fermi level, an instantaneous and significantly stronger demagnetization is observed, above the Fermi level, the demagnetization is delayed by 35 ± 10 fs. This provides a direct visualization of how ultrafast demagnetization proceeds via initial spin-flip scattering of laser-excited holes to the subsequent formation of spin waves.
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| 2. |
- Parchenko, Sergii, et al.
(författare)
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Orbital dynamics during an ultrafast insulator to metal transition
- 2020
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Ingår i: Physical Review Research. - : AMER PHYSICAL SOC. - 2643-1564. ; 2:2
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Tidskriftsartikel (refereegranskat)abstract
- We present ultrafast resonant inelastic x-ray scattering (RIXS) experiments performed at the vanadium L edge to track changes in the electronic structure of V2O3, a classical Mott-Hubbard material. The probed orbital excitations within the d shell of the V ion show a sub-ps time response, which evolves at later times to a state that appears electronically indistinguishable from the high-temperature metallic state. For low excitation fluences, a transient recovery or delay is observed, which could be related to a transient dimerization of the V-V bonds. Our results demonstrate the great potential for RIXS spectroscopy to study the ultrafast orbital dynamics in strongly correlated materials.
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| 3. |
- Porat, G., et al.
(författare)
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Phase-matched extreme-ultraviolet frequency-comb generation
- 2019
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Ingår i: Ultrafast Optics XII. - 1996-756X .- 0277-786X. - 9781510635128 ; 11370, s. 94-95
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Konferensbidrag (refereegranskat)abstract
- Extreme ultraviolet (XUV) laser radiation is commonly produced via high-harmonic generation (HHG) in gases. The lasers that drive this process typically operate at low pulse repetition rates (<100 kHz). Under these operating conditions, the plasma generated by each laser pulse clears the generation volume before the next pulse arrives. Therefore, each laser pulse interacts with fresh plasma-free gas, where phase-matching facilitates efficient HHG. However, applications requiring high counting statistics or frequency-comb precision make high repetition rates (>10 MHz) necessary. Unfortunately, at high repetition rates, plasma accumulates in the XUV generation region and prevents phase-matching, resulting in low HHG efficiency. We use high-temperature gas mixtures to increase the gas translational velocity, thus reduce plasma accumulation and facilitate phase-matching. We experimentally achieve phase-matched HHG at a repetition rate of 77 MHz, generating record power of ~2 mW at 97 nm and ~0.9 mW at 67 nm.
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| 4. |
- Schreck, Simon, et al.
(författare)
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Atom-specific activation in CO oxidation
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:23
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Tidskriftsartikel (refereegranskat)abstract
- We report on atom-specific activation of CO oxidation on Ru(0001) via resonant X-ray excitation. We show that resonant 1s core-level excitation of atomically adsorbed oxygen in the co-adsorbed phase of CO and oxygen directly drives CO oxidation. We separate this direct resonant channel from indirectly driven oxidation via X-ray induced substrate heating. Based on density functional theory calculations, we identify the valence-excited state created by the Auger decay as the driving electronic state for direct CO oxidation. We utilized the fresh-slice multi-pulse mode at the Linac Coherent Light Source that provided time-overlapped and 30 fs delayed pairs of soft X-ray pulses and discuss the prospects of femtosecond X-ray pump X-ray spectroscopy probe, as well as X-ray two-pulse correlation measurements for fundamental investigations of chemical reactions via selective X-ray excitation.
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| 5. |
- Zusin, Dmitriy, et al.
(författare)
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Ultrafast perturbation of magnetic domains by optical pumping in a ferromagnetic multilayer
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:14
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast optical pumping of spatially nonuniform magnetic textures is known to induce far-from-equilibrium spin transport effects. Here, we use ultrafast x-ray diffraction with unprecedented dynamic range to study the laser-induced dynamics of labyrinth domain networks in ferromagnetic CoFe/Ni multilayers. We detected azimuthally isotropic, odd order, magnetic diffraction rings up to fifth order. The amplitudes of all three diffraction rings quench to different degrees within 1.6 ps. In addition, all three of the detected diffraction rings both broaden by 15% and radially contract by 6% during the quench process. We are able to rigorously quantify a 31% ultrafast broadening of the domain walls via Fourier analysis of the order-dependent quenching of the three detected diffraction rings. The broadening of the diffraction rings is interpreted as a reduction in the domain coherence length, but the shift in the ring radius, while unambiguous in its occurrence, remains unexplained. In particular, we demonstrate that a radial shift explained by domain-wall broadening can be ruled out. With the unprecedented dynamic range of our data, our results provide convincing evidence that labyrinth domain structures are spatially perturbed at ultrafast speeds under far-from-equilibrium conditions, albeit the mechanism inducing the perturbations remains yet to be clarified.
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