We are excited to share our latest pre-print on “Saturable absorption of free-electron laser radiation by graphite near the carbon K-edge”. In this experiment, we study in a single experiment supported by state-of-the-art numerical simulations how intense femtosecond X-ray free-electron laser pulses induce two different nonlinear responses, saturable absorption (SA) and two-photon absorption (TPA), depending on intensity. Our data suggests that SA and TPA are competing processes in the X-ray regime and the relative transition strengths determine at which intensities TPA becomes dominant over SA which is ultimately a material-specific property. Our results reveal the competing contributions of distinct nonlinear material responses to spectroscopic signals measured in the X-ray regime, demonstrating an approach of general utility for interpreting FEL spectroscopies. This opens new routes for dynamically probing properties of matter.

Congrats to Lars for his first submitted manuscript in the group.

This work was done in collaboration with researchers from the Saykally group at UCB, LBNL, U of Texas Rio Grande Valley, UC San Diego, and FERMI. The experiments were conducted at the free-electron laser facility FERMI in Italy.

Pre-print available here:
https://arxiv.org/abs/2112.12585