Multielectron-Ion Coincidence Spectroscopy of Xe in Extreme Ultraviolet Laser Fields: Nonlinear Multiple Ionization via Double Core-Hole States

Multiple Sequential Ionization of Valence n = 4 Shell of Krypton by Intense Femtosecond XUV Pulses

Sequential photoionization of krypton by intense extreme ultraviolet femtosecond pulses is studied theoretically for the photon energies below the 3d excitation threshold. This regime with energetically forbidden Auger decay is characterized by special features, such as time scaling of the level population. The model is based on the solution of rate equations with photoionization cross sections of krypton in different charge and multiplet states determined using R-matrix calculations. Predictions of the ion yields and photoelectron spectra for various photon fluence are presented and discussed.

Demonstration of Transmission Mode Soft X-ray NEXAFS Using Third- and Fifth-Order Harmonics of FEL Radiation at SACLA BL1

We demonstrate the applicability of third- and fifth-order harmonics of free-electron laser (FEL) radiation for soft X-ray absorption spectroscopy in the transmission mode at SACLA BL1, which covers a photon energy range of 20 to 150 eV in the fundamental FEL radiation. By using the third- and fifth-order harmonics of the FEL radiation, we successfully recorded near-edge X-ray absorption fine structure (NEXAFS) spectra for Ar 2p core ionization and CO2 C 1s and O 1s core ionizations. Our results show that the utilization of third- and fifth-order harmonics can significantly extend the available photon energies for NEXAFS spectroscopy using an FEL and opens the door to femtosecond pump-probe NEXAFS using a soft X-ray FEL.