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内容記述 |
Photoelectron-photoion coincidence momentum imaging has been performed to investigate excitation processes on dissociative ionization of OCS in phase-locked ω+2ω intense laser fields. The electron kinetic energy spectra depend on the ion speicies, OCS^+ or S^+, produced in coincidence. The observed electron momentum distribution shows clear asymmetry along the laser polarization direction with a 2π-oscillation period as a function of the phase difference between the ω and 2ω laser fields. The asymmetry of electron emission in the OCS^+ channel flips at the electron kinetic energy of 8.2 eV, below which forward-scattered electrons dominate and above which backward-scattered electrons dominate. In the S^+ channel, the asymmetry flips at the lower kinetic energy of 4.2 eV. In comparison with a classical trajectory Monte Carlo simulation, it has been clarified that this energy shift between the OCS^+ and S^+ channels corresponds to the excitation energy of the parent ion and that electron recollisional excitation takes place to form the fragment ion in intense laser fields. |
