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Rivas, D. E.; Major, B.; Weidman, M.; Helml, W.; Marcus, G.; Kienberger, R.; Charalambidis, D.; Tzallas, P.; Balogh, E.; Kovacs, K.; Tosa, V; Bergues, B.; Varju, K.; Veisz, L. (2018): Propagation-enhanced generation of intense high-harmonic continua in the 100-eV spectral region. In: Optica, Vol. 5, No. 10: pp. 1283-1289
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The study of core electron dynamics through nonlinear spectroscopy requires intense isolated attosecond extreme ultraviolet or even X-ray pulses. A robust way to produce these pulses is high-harmonic generation (HHG) in a gas medium. However, the energy upscaling of the process depends on a very demanding next-generation laser technology that provides multi-terawatt (TW) laser pulses with few-optical-cycle duration and controlled electric field. Here, we revisit the HHG process driven by 16-TW sub-two-cycle laser pulses to reach high intensity in the 100-eV spectral region and beyond. We show that the combination of above barrier-suppression intensity with a long generation medium significantly enhances the isolation of attosecond pulses compared to lower intensities and/or shorter media and this way reduces the pulse duration as well as field-stability requirements on the laser driver. This novel regime facilitates the real-time observation of electron dynamics at the attosecond timescale in atoms, molecules, and solids.