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Channel coupling and threshold effects on multiphoton processes involving a weakly bound electron interacting with an intense laser field

Ioan-Bogdan Borca, University of Nebraska - Lincoln


In this dissertation are investigated several aspects of the interaction between an intense laser and an atomic system that can be described by one electron bound in a short range potential. The model used is relevant to alkali negative ions and especially H. The effects discussed here have a common origin in the coupling between various multiphoton interaction channels. The two kinds of processes in which these effects are revealed are multiphoton detachment and harmonic generation. ^ The first effect discussed is elliptic dichroism (ED), which is defined as the dependence of the value of an observable quantity on the sign of the helicity of the laser; this dependence vanishes for pure linear or circular polarization. Its origin is related to the presence of dissipative processes, i.e., alternative channels which compete with the observed one. The dependence of the ED on laser intensity and frequency is studied for electron angular distributions following multiphoton detachment. In addition, unusual angular distributions are found close to multiphoton detachment thresholds. The ED effect is shown to exist in the case of harmonic generation in the presence of a static electric field. ^ The second part of this work concerns the effects of any particular multiphoton detachment threshold on higher multiphoton detachment channels as well as on harmonic generation channels. The largest effects are localized in the well-known plateau part of the spectra. Threshold anomalies offer a simple and familiar qualitative explanation of recent experimental observations of resonance-like enhancements of multiphoton ionization spectra for rare gases at the closing of low-order ATT channels. For harmonic generation, analytical and numerical results show that the dynamics of the process is essentially governed by the threshold phenomena of multichannel reaction theory and quantitatively explain features seen in recent experiments and numerical simulations. ^

Subject Area

Physics, Atomic|Physics, Optics

Recommended Citation

Borca, Ioan-Bogdan, "Channel coupling and threshold effects on multiphoton processes involving a weakly bound electron interacting with an intense laser field" (2001). ETD collection for University of Nebraska - Lincoln. AAI3034364.