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Updated: Aug 27, 2025

Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle
Published on: September 22, 2015
Saturable Absorption of Free-Electron Laser Radiation by Graphite near the Carbon K-Edge
Lars Hoffmann1,2,3, Sasawat Jamnuch4, Craig P Schwartz2,5
1Department of Chemistry, University of California, Berkeley, California 94720, United States.
Abstract:
The interaction of intense light with matter gives rise to competing nonlinear responses that can dynamically change material properties. Prominent examples are saturable absorption (SA) and two-photon absorption (TPA), which dynamically increase and decrease the transmission of a sample depending on pulse intensity, respectively. The availability of intense soft X-ray pulses from free-electron lasers (FELs) has led to observations of SA and TPA in separate experiments, leaving open questions about the possible interplay between and relative strength of the two phenomena. Here, we systematically study both phenomena in one experiment by exposing graphite films to soft X-ray FEL pulses of varying intensity. By applying real-time electronic structure calculations, we find that for lower intensities the nonlinear contribution to the absorption is dominated by SA attributed to ground-state depletion; our model suggests that TPA becomes more dominant for larger intensities (>1014 W/cm2). Our results demonstrate an approach of general utility for interpreting FEL spectroscopies.
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