Abstract:
By implementing a time-independent, nonperturbative many-electron, many-photon theory (MEMPT), cycle-averaged complex eigenvalues were obtained for the He atom, whose real part gives the field-induced energy shift, Δ(ω 1, F 1;ω 2, F 2,ϕ), and the imaginary part is the multiphoton ionization rate, Γ(ω 1, F 1;ω 2, F 2,ϕ), where ω is the frequency, F is the field strength and ϕ is the phase difference. Through analysis and computation we show that, provided the intensities are weak, the dependence of Γ(ω 1, F 1;ω 2, F 2,ϕ) on ϕ is simple. Specifically, for odd harmonics, Γ varies linearly with cos(ϕ) whilst for even harmonics it varies linearly with cos(2ϕ). In addition, this dependence on ϕ holds for Δ(ω 1, F 1;ω 2, F 2,ϕ) as well. These relations may turn out to be applicable to other atomic systems as well, and to provide a definition of the weak field regime in the dichromatic case. When the combination of (ω 1, F 1) and (ω 2, F 2) is such that higher powers of cos(ϕ) and cos(2ϕ) become important, these rules break down and we reach the strong field regime. The herein reported results refer to Γ(ω 1, F 1;ω 2, F 2,ϕ) and Δ(ω 1, F 1;ω 2, F 2,ϕ) for He irradiated by a dichromatic ac-field consisting of the fundamental wavelength λ = 248 nm and its 2nd, 3rd and 4th higher harmonics. The intensities are in the range 1.0×1012-3.5×1014 W/cm2, with the intensity of the harmonics being 1-2 orders of magnitude smaller. The calculations incorporated systematically electronic structure and electron correlation effects in the discrete and in the continuous spectrum, for 1S, 1P, 1D, 1F, 1G, and 1H two-electron states of even and odd parity.
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Received 9 July 2000 and Received in final form 2 November 2000
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Mercouris, T., Nicolaides, C. The multiphoton ionization rate and the energy shift of atoms interacting with weak dichromatic fields with commensurate frequencies are simple functions of the phase difference. Eur. Phys. J. D 14, 241–248 (2001). https://doi.org/10.1007/s100530170222
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DOI: https://doi.org/10.1007/s100530170222