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 puls...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 femtosec ond FEL pulses,which we exploit for fine self-driven spectral tun ability 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 account!ng for ultrafast ionization and delayed thermal response of highly excited electrons above and below threshold,respectively.展开更多
基金the European Union's Horizon 2020 research and innovation programme Graphene Flagship tinder grant agreement No 881603 and from PRIN 2017 Project 201795SBA3 HARVEST.
文摘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 femtosec ond FEL pulses,which we exploit for fine self-driven spectral tun ability 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 account!ng for ultrafast ionization and delayed thermal response of highly excited electrons above and below threshold,respectively.
