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arXiv · 2203.11021

High-harmonic generation in a strongly overdriven regime

B. Major·K. Kovács·E. Svirplys·M. Anus·O. Ghafur·K. Varjú·M. J. J. Vrakking·V. Tosa·B. Schütte
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Abstract

High-harmonic generation (HHG) normally requires a careful adjustment of the driving laser intensity (typically $10^{14} - 10^{15}$ W/cm$^2$) and gas medium parameters to enable good phase matching conditions. In contrast with conventional wisdom, we present experimental results indicating phase-matched HHG in all rare gases, using a high-density medium and a driver laser intensity of around $10^{16}$ W/cm$^2$. The experimental results are corroborated by theoretical simulations, which indicate that ionization-induced self-phase modulation and plasma defocusing self-regulate the driver laser intensity to a level that is appropriate for good phase matching. A ten-fold broadening of the NIR spectrum is observed, which results in the generation of continuous spectra from $18-140$ eV in spite of using 50-fs-long driving pulses. The presented scheme represents a simple and versatile concept for the generation of XUV and soft X-ray continua, which are ideally suited for transient absorption and reflection spectroscopy.

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B. Major, K. Kovács, E. Svirplys, M. Anus, O. Ghafur, K. Varjú, M. J. J. Vrakking, V. Tosa, B. Schütte. 2022-03-21. High-harmonic generation in a strongly overdriven regime. https://doi.org/10.1103/physreva.107.023514

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