Autoionizing states in two-photon double ionization of Beryllium: Application of finite-pulse virtual-sequential model

Intense ultrashort XFEL and XUV sources have opened the way to XUV-pump XUV-probe spectroscopies, which allow one to observe correlated electron dynamics in atoms and molecules with unprecedented time resolution [1-3]. Two-photon double ionization (TPDI) processes are of particular interest as they can allow us to monitor the correlated motion of electron pairs prior to photoemission. Most of the complex dynamics unfolding in TPDI experiments is well reproduced by a recently developed finite-pulse virtual sequential model (FPVSM) [4, 5], which we have implemented for both general atoms and molecules and can reproduce angularly integrated TPDI observables at a fraction of the computational cost required by explicit TDSE solvers. Here, we present a theoretical study of the TPDI of Beryllium using the FPVSM model. This system is interesting due to the presence of autoionizing series in the correlation-dominated non-sequential region. Our simulations resolve the interplay between sequential and non-sequential TPDI pathways and observe a clear signature of autoionizing states in the joint energy distribution for the two photoelectrons. This work serves as a benchmark prediction for experiments exploring TPDI of complex atoms and paves the way to time-resolved study and control of concerted electronic motion in atoms and molecules.

[1] M. Rini, First light for a next-generation light source, Physics 16, 160 (2023) 

[2] Z. Guo et al., Nat. Photonics 18, 691 (2024).

[3] M. Kretschmar et al., Science Advances 10 eadk9605 (2024)

[4] S. Chattopadhyay et al., Phys. Rev. A 108 013114 (2023) 

[5] S. Chattopadhyay et al., Phys. Rev. A 110 013106 (2024)