Light: Science & Applications (Apr 2021)

Non-linear self-driven spectral tuning of Extreme Ultraviolet Femtosecond Pulses in monoatomic materials

  • Carino Ferrante,
  • Emiliano Principi,
  • Andrea Marini,
  • Giovanni Batignani,
  • Giuseppe Fumero,
  • Alessandra Virga,
  • Laura Foglia,
  • Riccardo Mincigrucci,
  • Alberto Simoncig,
  • Carlo Spezzani,
  • Claudio Masciovecchio,
  • Tullio Scopigno

DOI
https://doi.org/10.1038/s41377-021-00531-8
Journal volume & issue
Vol. 10, no. 1
pp. 1 – 7

Abstract

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Abstract Self-action nonlinearity is a key aspect – either as a foundational element or a detrimental factor – of several optical spectroscopies and photonic devices. Supercontinuum generation, wavelength converters, and chirped pulse amplification are just a few examples. The recent advent of Free Electron Lasers (FEL) fostered building on nonlinearity to propose new concepts and extend optical wavelengths paradigms for extreme ultraviolet (EUV) and X-ray regimes. No evidence for intrapulse dynamics, however, has been reported at such short wavelengths, where the light-matter interactions are ruled by the sharp absorption edges of core electrons. Here, we provide experimental evidence for self-phase modulation of femtosecond FEL pulses, which we exploit for fine self-driven spectral tunability by interaction with sub-micrometric foils of selected monoatomic materials. Moving the pulse wavelength across the absorption edge, the spectral profile changes from a non-linear spectral blue-shift to a red-shifted broadening. These findings are rationalized accounting for ultrafast ionization and delayed thermal response of highly excited electrons above and below threshold, respectively.