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High power, high repetition rate laser-based sources for attosecond science
2022, Furch, F.J., Witting, T., Osolodkov, M., Schell, F., Schulz, C.P., Vrakking, M.J.
Within the last two decades attosecond science has been established as a novel research field providing insights into the ultrafast electron dynamics that follows a photoexcitation or photoionization process. Enabled by technological advances in ultrafast laser amplifiers, attosecond science has been in turn, a powerful engine driving the development of novel sources of intense ultrafast laser pulses. This article focuses on the development of high repetition rate laser-based sources delivering high energy pulses with a duration of only a few optical cycles, for applications in attosecond science. In particular, a high power, high repetition rate optical parametric chirped pulse amplification system is described, which was developed to drive an attosecond pump-probe beamline targeting photoionization experiments with electron-ion coincidence detection at high acquisition rates.
Highly non-linear ionization of atoms induced by intense high-harmonic pulses
2020, Senfftleben, B., Kretschmar, M., Hoffmann, A., Sauppe, M., Tümmler, J., Will, I., Nagy, T., Vrakking, M.J.J., Rupp, D., Schütte, B.
Intense extreme-ultraviolet (XUV) pulses enable the investigation of XUV-induced non-linear processes and are a prerequisite for the development of attosecond pump - attosecond probe experiments. While highly non-linear processes in the XUV range have been studied at free-electron lasers (FELs), high-harmonic generation (HHG) has allowed the investigation of low-order non-linear processes. Here we suggest a concept to optimize the HHG intensity, which surprisingly requires a scaling of the experimental parameters that differs substantially from optimizing the HHG pulse energy. As a result, we are able to study highly non-linear processes in the XUV range using a driving laser with a modest (˜ 10 mJ) pulse energy. We demonstrate our approach by ionizing Ar atoms up to Ar5 + , requiring the absorption of at least 10 XUV photons. © 2020 The Author(s). Published by IOP Publishing Ltd
Propagation-assisted generation of intense few-femtosecond high-harmonic pulses
2020, Major, B., Kretschmar, M., Ghafur, O., Hoffmann, A., Kovács, K., Varjú, K., Senfftleben, B., Tümmler, J., Will, I., Nagy, T., Rupp, D., Vrakking, M.J.J., Tosa, V., Schütte, B.
The ongoing development of intense high-harmonic generation (HHG) sources has recently enabled highly non-linear ionization of atoms by the absorption of at least 10 extreme-ultraviolet (XUV) photons within a single atom (Senfftleben et al, arXiv:1911.01375). Here we investigate how the generation of these very intense HHG pulses in our 18-m-long beamline is aided by the reshaping of the fundamental, few-cycle, near-infrared (NIR) driving laser within a 30-cm-long HHG Xe medium. Using an incident NIR intensity that is higher than what is required for phase-matched HHG, signatures of reshaping are found by measuring the NIR blueshift and the fluorescence from the HHG medium along the propagation axis. These results are well reproduced by numerical calculations that show temporal compression of the NIR pulses in the HHG medium. The simulations predict that after refocusing an XUV beam waist radius of 320 nm and a clean attosecond pulse train can be obtained in the focal plane, with an estimated XUV peak intensity of 9 × 1015 W cm-2. Our results show that XUV intensities that were previously only available at large-scale facilities can now be obtained using moderately powerful table-top light sources. © 2020 The Author(s). Published by IOP Publishing Ltd