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- ItemGeneration and characterization of isolated attosecond pulses for coincidence spectroscopy at 100 kHz repetition rate(Bristol : IOP Publ., 2020) Witting, T.; Furch, F.; Osolodkov, M.; Schell, F.; Menoni, C.; Schulz, C.P.; Vrakking, M.J.J.An attosecond pump-probe beamline with 100 kHz repetition rate for coincidence experiments has been developed. It is based on non-collinear optical parametric chirped pulse ampli-cation and delivers 100 µJ sub-4 fs to an high-harmonic generation source. Details on the generation and characterization of isolated attosecond pulses will be presented. © 2019 Published under licence by IOP Publishing Ltd.
- ItemOptimization of quantum trajectories driven by strong-field waveforms(College Park : American Institute of Physics Inc., 2014) Haessler, S.; Balciunas, T.; Fan, G.; Andriukaitis, G.; Pugžlys, A.; Baltuška, A.; Witting, T.; Squibb, R.; Zaïr, A.; Tisch, J.W.G.; Marangos; Chipperfield, L.E.Quasifree field-driven electron trajectories are a key element of strong-field dynamics. Upon recollision with the parent ion, the energy transferred from the field to the electron may be released as attosecondduration extreme ultaviolet emission in the process of high-harmonic generation. The conventional sinusoidal driver fields set limitations on the maximum value of this energy transfer and the efficient return of the launched electron trajectories. It has been predicted that these limits can be significantly exceeded by an appropriately ramped-up cycle shape [L. E. Chipperfield et al., Phys. Rev. Lett. 102, 063003 (2009)]. Here, we present an experimental realization of similar cycle-shaped waveforms and demonstrate control of the high-harmonic generation process on the single-atom quantum level via attosecond steering of the electron trajectories.With our improved optical cycles, we boost the field ionization launching the electron trajectories, increase the subsequent field-to-electron energy transfer, and reduce the trajectory duration. We demonstrate, in realistic experimental conditions, 2 orders of magnitude enhancement of the generated extreme ultraviolet flux together with an increased spectral extension. This application, which is only one example of what can be achieved with cycle-shaped high-field light waves, has significant implications for attosecond spectroscopy and molecular self-probing.
- ItemAttosecond control of electron-ion recollision in high harmonic generation(Bristol : IOP, 2011) Gademann, G.; Kelkensberg, F.; Siu, W.K.; Johnsson, P.; Gaarde, M.B.; Schafer, K.J.; Vrakking, M.J.J.We show that high harmonic generation driven by an intense nearinfrared (IR) laser can be temporally controlled when an attosecond pulse train (APT) is used to ionize the generation medium, thereby replacing tunnel ionization as the first step in the well-known three-step model. New harmonics are formed when the ionization occurs at a well-defined time within the optical cycle of the IR field. The use of APT-created electron wave packets affords new avenues for the study and application of harmonic generation. In the present experiment, this makes it possible to study harmonic generation at IR intensities where tunnel ionization does not give a measurable signal.
- ItemRecent developments in R-matrix applications to molecular processes(Bristol : IOP Publ., 2015) Mašín, Zdeněk; Harvey, Alex; Houfek, Karel; Brambila, Danilo S.; Morales, Felipe; Gorfinkiel, Jimena D.; Tennyson, Jonathan; Smirnova, OlgaWe report on recent developments of the UKRmol suite, an implementation of the molecular R- matrix method and present examples of the calculations (e.g. electron scattering, photoionization, high harmonic generation, etc.) it has enabled.
- ItemElement-specific magnetization dynamics of complex magnetic systems probed by ultrafast magneto-optical spectroscopy(Basel : MDPI, 2020) Korff Schmising, Clemens von; Willems, Felix; Sharma, Sangeeta; Yao, Kelvin; Borchert, Martin; Hennecke, Martin; Schick, Daniel; Radu, Ilie; Strüber, Christian; Engel, Dieter W.; Shokeen, Vishal; Buck, Jens; Bagschik, Kai; Viefhaus, Jens; Hartmann, Gregor; Manschwetus, Bastian; Grunewald, Soeren; Düsterer, Stefan; Jal, Emmanuelle; Vodungbo, Boris; Lüning, Jan; Eisebitt, StefanThe vision to manipulate and control magnetism with light is driven on the one hand by fundamental questions of direct and indirect photon-spin interactions, and on the other hand by the necessity to cope with ever growing data volumes, requiring radically new approaches on how to write, read and process information. Here, we present two complementary experimental geometries to access the element-specific magnetization dynamics of complex magnetic systems via ultrafast magneto-optical spectroscopy in the extreme ultraviolet spectral range. First, we employ linearly polarized radiation of a free electron laser facility to demonstrate decoupled dynamics of the two sublattices of an FeGd alloy, a prerequisite for all-optical magnetization switching. Second, we use circularly polarized radiation generated in a laboratory-based high harmonic generation setup to show optical inter-site spin transfer in a CoPt alloy, a mechanism which only very recently has been predicted to mediate ultrafast metamagnetic phase transitions. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemCompact intense extreme-ultraviolet source(Washington, DC : OSA, 2021) Major, Balázs; Ghafur, Omair; Kovács, Katalin; Varjú, Katalin; Tosa, Valer; Vrakking, Marc J. J.; Schütte, B.High-intensity laser pulses covering the ultraviolet to terahertz spectral regions are nowadays routinely generated in a large number of laboratories. In contrast, intense extreme-ultraviolet (XUV) pulses have only been demonstrated using a small number of sources including free-electron laser facilities [1-3] and long high-harmonic generation (HHG) beamlines [4-9]. Here we demonstrate a concept for a compact intense XUV source based on HHG that is focused to an intensity of $2 \times 10^{14}$ W/cm$^2$, with a potential increase up to $10^{17}$ W/cm$^2$ in the future. Our approach uses tight focusing of the near-infrared (NIR) driving laser and minimizes the XUV virtual source size by generating harmonics several Rayleigh lengths away from the NIR focus. Accordingly, the XUV pulses can be refocused to a small beam waist radius of 600 nm, enabling the absorption of up to four XUV photons by a single Ar atom in a setup that fits on a modest (2 m) laser table. Our concept represents a straightforward approach for the generation of intense XUV pulses in many laboratories, providing novel opportunities for XUV strong-field and nonlinear optics experiments, for XUV-pump XUV-probe spectroscopy and for the coherent diffractive imaging of nanoscale structures.
- ItemUsing the third state of matter: High harmonic generation from liquid targets(Bristol : IOP, 2014) Heissler, P.; Lugovoy, E.; Hörlein, R.; Waldecker, L.; Wenz, J.; Heigoldt, M.; Khrennikov, K.; Karsch, S.; Krausz, F.; Abel, B.; Tsakiris, G.D.High harmonic generation on solid and gaseous targets has been proven to be a powerful platform for the generation of attosecond pulses. Here we demonstrate a novel technique for the XUV generation on a smooth liquid surface target in vacuum, which circumvents the problem of low repetition rate and limited shot numbers associated with solid targets, while it maintains some of its merits. We employed atomically smooth, continuous liquid jets of water, aqueous salt solutions and ethanol that allow uninterrupted high harmonic generation due to the coherent wake emission mechanism for over 8 h. It has been found that the mechanism of plasma generation is very similar to that for smooth solid target surfaces. The vapor pressure around the liquid target in our setup has been found to be very low such that the presence of the gas phase around the liquid jet could be neglected.
- ItemTracking ultrafast solid-state dynamics using high harmonic spectroscopy(College Park, MD : APS, 2021) Bionta, Mina R.; Haddad, Elissa; Leblanc, Adrien; Gruson, Vincent; Lassonde, Philippe; Ibrahim, Heide; Chaillou, Jérémie; Émond, Nicolas; Otto, Martin R.; Siwick, Bradley J.; Chaker, Mohamed; Légaré, FrançoisWWe establish time-resolved high harmonic generation (tr-HHG) as a powerful spectroscopy method for tracking photoinduced dynamics in strongly correlated materials through a detailed investigation of the insulator-to-metal phase transitions in vanadium dioxide. We benchmark the technique by comparing our measurements to established momentum-resolved ultrafast electron diffraction, and theoretical density functional calculations. Tr-HHG allows distinguishing of individual dynamic channels, including a transition to a thermodynamically hidden phase. In addition, the HHG yield is shown to be modulated at a frequency characteristic of a coherent phonon of the equilibrium monoclinic phase over a wide range of excitation fluences. These results demonstrate that tr-HHG is capable of tracking complex dynamics in solids through its sensitivity to the band structure.