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Type: Article × Subject: resonance ×

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Now showing 1 - 3 of 3
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    Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation
    ([London] : Nature Publishing Group UK, 2015) Ferré, A.; Boguslavskiy, A.E.; Dagan, M.; Blanchet, V.; Bruner, B.D.; Burgy, F.; Camper, A.; Descamps, D.; Fabre, B.; Fedorov, N.; Gaudin, J.; Geoffroy, G.; Mikosch, J.; Patchkovskii, S.; Petit, S.; Ruchon, T.; Soifer, H.; Staedter, D.; Wilkinson, I.; Stolow, A.; Dudovich, N.; Mairesse, Y.
    High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected.
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    Anisotropic photoemission time delays close to a Fano resonance
    ([London] : Nature Publishing Group UK, 2018) Cirelli, Claudio; Marante, Carlos; Heuser, Sebastian; Petersson, C.L.M.; Galán, Álvaro Jiménez; Argenti, Luca; Zhong, Shiyang; Busto, David; Isinger, Marcus; Nandi, Saikat; Maclot, Sylvain; Rading, Linnea; Johnsson, Per; Gisselbrecht, Mathieu; Lucchini, Matteo; Gallmann, Lukas; Dahlström, J. Marcus; Lindroth, Eva; L’Huillier, Anne; Martín, Fernando; Keller, Ursula
    Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of autoionization, induced by resonant excitation of electrons into discrete states present in the spectral continuum of atomic and molecular targets, is mediated by electron correlation. Here we investigate the attosecond photoemission dynamics in argon in the 20-40 eV spectral range, in the vicinity of the 3s -1 np autoionizing resonances. We present measurements of the differential photoionization cross section and extract energy and angle-dependent atomic time delays with an attosecond interferometric method. With the support of a theoretical model, we are able to attribute a large part of the measured time delay anisotropy to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.
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    Noninvasive Estimation of Water Retention Parameters by Observing the Capillary Fringe with Magnetic Resonance Sounding
    (Hoboken, NJ : Wiley, 2014) Costabel, Stephan; Günther, Thomas
    The magnetic resonance sounding (MRS) method is usually applied for delineation and characterization of aquifer system stratification. Its unique property, distinct from other hydrogeophysical methods, is the direct sensitivity to water content in the subsurface. The inversion of MRS data yields the subsurface water content distribution without need of a petrophysical model. Recent developments in instrumentation, i.e., decreased instrumental dead times and advanced noise cancellation strategies, enable the use of this method for investigating the vadose zone. A possible way to interpret MRS measurements with focus on water retention (WR) parameters is an inversion approach that directly provides WR parameters by modeling the capillary fringe (CF inversion). We have developed this kind of inversion further to account for different WR models and present a sensitivity study based on both synthetic and real field data. To assess the general applicability of the CF inversion, we analyzed the resolution properties for different measurement layouts and the parameter uncertainties for different realistic scenarios. Under moderate noise conditions and if the water table position is known, all WR parameters except the residual water content can be reliably estimated. The relative accuracy of the estimated pore distribution index estimation is better for larger CF. Small measurement loops of 5-m diameter achieve the best resolution for shallow investigation depths of <10 m.