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Optics Express

Role of atomic coherence in the propagation of two-color lasers in an autoionizing medium

Takashi Nakajima

Published Jan 1, 2007• 0 citations
Publisher

Abstract

We study the role of atomic coherence in the propagation dynamics of two-color lasers in an autoionizing medium. By solving the coupled equations for atoms and fields simultaneously, it is found that the asymptotic value of the phase difference after a long propagation distance critically depends on the detuning from an autoionizing resonance and the asymmetry parameter, suggesting that inherent atomic coherence of an autoionizing system, which is absent in a bound state system, plays an important role during the propagation processes. Our numerical findings are consistent with our theoretical analysis using a series expansion method of the coupled equations.

DOI
10.1364/oe.15.005721

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We study the role of atomic coherence in the propagation dynamics of two-color lasers in an autoionizing medium. By solving the coupled equations for atoms and fields simultaneously, it is found that the asymptotic value of the phase difference after a long propagation distance critically depends on the detuning from an autoionizing resonance and the asymmetry parameter, suggesting that inherent atomic coherence of an autoionizing system, which is absent in a bound state system, plays an important role during the propagation processes. Our numerical findings are consistent with our theoretical analysis using a series expansion method of the coupled equations.
We present a self-consistent theory and analytical results for the three-photon-one-photon coherent control of ionization in an optically dense autoionizing medium. We show that for an optically thick medium, over a short scaled propagation distance, the phase and amplitude of the harmonic field settle to values that are fully determined by the atomic and fundamental field parameters and are completely independent of the initial relative phase between the two fields, thus preventing efficient phase control of the autoionization and its products. Control of the autoionization and the branching ratio of its products is still feasible, however, through the variation of the detuning of the fundamental field from the atomic transition resonance.
We present the experimental and theoretical investigation of the effects of the strong electromagnetic coupling of two autoionizing states (AIS's) on the photoionization properties of an atomic system. These effects are observed by probing the ladder system from the ground state of the atom through a weak two-photon transition to the region of the lower AIS. The experimental observation of the modification of the total ionization and partial photoelectron spectra at different wavelengths of the coupling and probe lasers are accurately reproduced by a theoretical analysis which uses a density-matrix approach. Both theory and experiment indicate a strong inhibition of the ionization of the system in the case when both lasers are resonant with the two atomic transitions, while displaying a rapidly varying asymmetry induced as the detuning between the two states and the fields increases. In the extreme case of a large detuning, two separate structures appear as distinct total ionization and photoelectron peaks. The above findings combined with the full theoretical treatment indicate that the phenomena observed are an experimental demonstration of ac Stark splitting between two AIS's. \textcopyright{} 1996 The American Physical Society.
We theoretically study intensity-saturation effects in resonant harmonic generation and multiphoton ionization. A first laser excites a two-photon resonance which is coupled by a second laser to an autoionizing state. Starting from an effective Hamiltonian for the three resonant atomic states, we derive a set of equations for the density matrix of the gaseous medium and the electromagnetic field within a semiclassical framework. We present and discuss analytical and numerical solutions of these equations which show a variety of line profiles depending critically on the intensities of the incident laser pulses.