Insights into Electron Excitation Processes in Intense Laser Fields

Recent research has explored the excitation processes involved in the dissociative ionization of OCS (carbonyl sulfide) in intense laser fields. The study, titled "Electron rescollisional excitation of OCS⁺ in phase-locked ω + 2ω intense laser fields," was conducted by Tomoyuki Endo, Tomohito Otobe, and Ryuji Itakura. The findings were published on arXiv and can be accessed here.

The researchers employed photoelectron-photoion coincidence momentum imaging to investigate how electron kinetic energy spectra vary based on the ion species produced during the ionization process. They observed that the electron momentum distribution exhibited a distinct asymmetry along the laser polarization direction, which oscillated with a period of 2π as a function of the phase difference in the ω + 2ω laser fields.

Notably, the study identified a critical point where the asymmetry of electron emission in the OCS⁺ channel flipped at an electron kinetic energy of 8.2 eV. This indicates a shift in the dominant scattering direction from forward to backward. In contrast, the S⁺ channel showed an asymmetry flip at a lower kinetic energy of 4.2 eV, which was linked to an inelastic scattering process.

The researchers compared their experimental results with classical trajectory Monte-Carlo simulations, concluding that the observed shifts in electron kinetic energy correspond to the excitation energy of the parent ion. This suggests that electron recollisional excitation plays a significant role in forming fragment ions in intense laser fields.

These findings contribute to a deeper understanding of the dynamics involved in laser-induced ionization processes, which could have implications for various applications in atomic and molecular physics, particularly in the development of advanced laser technologies.