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Author: Vrakking, Marc J.J. × Type: article × Publisher: Bristol : IOP Publ. × WGL Institute: MBI ×

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Now showing 1 - 4 of 4
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    Population transfer to high angular momentum states in infrared-assisted XUV photoionization of helium
    (Bristol : IOP Publ., 2020) Mayer, Nicola; Peng, Peng; Villeneuve, David M.; Patchkovskii, Serguei; Ivanov, Misha; Kornilov, Oleg; Vrakking, Marc J.J.; Niikura, Hiromichi
    An extreme-ultraviolet (XUV) laser pulse consisting of harmonics of a fundamental near-infrared (NIR) laser frequency is combined with the NIR pulse to systematically study two-color photoionization of helium atoms. A time-resolved photoelectron spectroscopy experiment is carried out where energy- A nd angle-resolved photoelectron distributions are obtained as a function of the NIR intensity and wavelength. Time-dependent Schrödinger equation calculations are performed for the conditions corresponding to the experiment and used to extract residual populations of Rydberg states resulting from excitation by the XUV + NIR pulse pair. The residual populations are studied as a function of the NIR intensity (3.5 × 1010-8 × 1012 W cm-2) and wavelength (760-820 nm). The evolution of the photoelectron distribution and the residual populations are interpreted using an effective restricted basis model, which includes the minimum set of states relevant to the features observed in the experiments. As a result, a comprehensive and intuitive picture of the laser-induced dynamics in helium atoms exposed to a two-color XUV-NIR light field is obtained. © 2020 The Author(s). Published by IOP Publishing Ltd.
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    Generation and characterisation of few-pulse attosecond pulse trains at 100 kHz repetition rate
    (Bristol : IOP Publ., 2020) Osolodkov, Mikhail; Furch, Federico J.; Schell, Felix; Šušnjar, Peter; Cavalcante, Fabio; Menoni, Carmen S.; Schulz, Claus P.; Witting, Tobias; Vrakking, Marc J.J.
    The development of attosecond pump-probe experiments at high repetition rate requires the development of novel attosecond sources maintaining a sufficient number of photons per pulse. We use 7 fs, 800 nm pulses from a non-collinear optical parametric chirped pulse amplification laser system to generate few-pulse attosecond pulse trains (APTs) with a flux of >106 photons per shot in the extreme ultraviolet at a repetition rate of 100 kHz. The pulse trains have been fully characterised by recording frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) traces with a velocity map imaging spectrometer. For the pulse retrieval from the FROG-CRAB trace a new ensemble retrieval algorithm has been employed that enables the reconstruction of the shape of the APTs in the presence of carrier envelope phase fluctuations of the few-cycle laser system. © 2020 The Author(s). Published by IOP Publishing Ltd.
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    Spatio-temporal characterisation of a 100 kHz 24 W sub-3-cycle NOPCPA laser system
    (Bristol : IOP Publ., 2018-02-26) Witting, Tobias; Furch, Federico J.; Vrakking, Marc J.J.
    In recent years, OPCPA and NOPCPA laser systems have shown the potential to supersede Ti:sapphire plus post-compression based laser systems to drive next generation attosecond light sources via direct amplification of few-cycle pulses to high pulse energies at high repetition rates. In this paper, we present a sub 3-cycle, 100 kHz, 24 W NOPA laser system and characterise its spatio-temporal properties using the SEA-F-SPIDER technique. Our results underline the importance of spatio-temporal diagnostics for these emerging laser systems.
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    Retrieval of attosecond pulse ensembles from streaking experiments using mixed state time-domain ptychography
    (Bristol : IOP Publ., 2020) Witting, Tobias; Furch, Federico J.; Kornilov, Oleg; Osolodkov, Mikhail; Schulz, Claus P.; Vrakking, Marc J.J.
    The electric field of attosecond laser pulses can be retrieved from laser-dressed photoionisation measurements, where electron wavepackets that result from single-photon ionisation by the attosecond pulse in the presence of a dressing field are produced. In case of fluctuating dressing laser and/or attosecond pulses, e.g. due to pulse-to-pulse fluctuations of the carrier envelope phase of the infrared laser pulse, commonly applied retrieval algorithms result in the erroneous extraction of the pulse fields. We present a mixed state time-domain ptychography algorithm for the retrieval of pulse ensembles from attosecond streaking experiments. © 2020 The Author(s). Published by IOP Publishing Ltd.