Multiple Excitation Processes in Photoionization

X. X. Lu, Lide Wang

Abstract The laser frequency spectrum, whose full width at half-maximum in the frequency domain is the laser bandwidth, plays a critical role in atomic multi-step photoionization processes and has a significant influence on isotopic selective photoionization results. In this study, two phase-independent frequency spectrum models, that is, the mode jitter model (MJ model) based on the mode jitter phenomenon and the multi-longitudinal mode model (MLM model) based on multi-longitudinal mode output, are proposed to describe the spectral characteristics in the frequency domain. In the MJ model, it is assumed that there is a time-varying longitudinal mode in each laser pulse, with different central frequencies between adjacent pulses in the pulse train; in the MLM model, it is assumed that multiple longitudinal modes are output simultaneously with fixed central frequencies. Selective photoionization properties of these two frequency spectrum models and the chaotic field model are simulated and compared with each other under the Lorentzian frequency spectrum condition. Influences of the excitation intensity, laser frequency spectral profile and cutoff frequency on selective photoionization processes are calculated and compared among the above-mentioned three frequency spectrum models. Finally, the measurement of the laser frequency spectrum and the introduction of individual longitudinal modes’ bandwidths are discussed.

Robert William Ditchburn, U. Öpik

M. Ya. Amusia

S Kim, S Steinhäuser, Alexander B Voitkiv +1 more

Abstract Ionization-excitation of an atom induced by the absorption of a single photon in the presence of a neighboring atom is studied. The latter is, first, resonantly photoexcited and, afterwards, transfers the excitation energy radiationlessly to the other atom, leading to its ionization with simultaneous excitation. The process relies on the combined effects of interatomic and intraatomic electron correlations. Under suitable conditions, it can dominate by several orders of magnitude over direct photoionization-excitation and even over direct photoionization. In addition, we briefly discuss another kind of two-center resonant photoionization with excitation where the ionization and residual excitation in the final state are located at different atomic sites.

Steven Trent Manson, Zikri Zikri, Altun ALTUN +3 more

Aleksei B D'yachkov, Sergei M. Mironov, Gleb O. Tsvetkov

Analytical solutions of the Schr?dinger equations for coherent excitation of an atom in the scheme of two- and three-stage photoionization are obtained as applied to the problem of laser isotope separation. A feature of the study is the introduction of laser excitation from an additional initial state to increase the fraction of the atoms involved in the separation process. The optimal from the points of view of photoion ratios of radiation intensities at individual photoionization stages are found. Key words: laser photoionization, laser isotope separation.