Yazar "Mese, E." seçeneğine göre listele

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    Öğe
    Multiphoton ionization and multiphoton resonances in the tunneling regime
    (Amer Physical Soc, 2010) Potvliege, R. M.; Mese, E.; Vucic, Svetlana
    The rate of ionization of an atom of helium, argon, or hydrogen exposed to an intense monochromatic laser field and the quasienergy spectrum of their dressed states are studied for values of the Keldysh parameter between 1 and 0.6 and wavelengths between 390 and 1300 nm. The calculations are carried out within the non-Hermitian Floquet theory. Resonances with intermediate excited states significantly affect ionization from the dressed ground state at all the intensities and all the wavelengths considered. The dressed excited states responsible for these structures are large-alpha(0) states akin to the Kramers-Henneberger states of the high-frequency Floquet theory. Within the single-active-electron approximation, these large-alpha(0) states become species independent at sufficiently high intensity or sufficiently long wavelength. Apart for the resonance structures arising from multiphoton coupling with excited states, the ab initio Floquet ionization rate is in excellent agreement with the predictions of two different calculations in the strong field approximation, one based on a length-gauge formulation of this approximation and one based on a velocity-gauge formulation. The calculations also confirm the validity of the omega(2) expansion as an alternative to the strong field approximation for taking into account the nonadiabaticity of the ionization process in intense low-frequency laser fields.
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    Öğe
    Quasienergy spectrum of complex atoms
    (Amer Physical Soc, 2008) Mese, E.; Potvliege, M.
    Representative sections of the quasienergy spectrum of argon and of alkali-metal atoms are presented for wavelengths between 250 nm and 800 nm and excursion amplitudes up to alpha(0)=20 a.u. The variation of the quasienergy spectrum with the wavelength of the laser field is discussed. It is shown that large-scale changes in its topology arise from laser-induced degeneracies with states without physical high-intensity or low-intensity limits.
  • [ X ]
    Öğe
    Theoretical calculation of saturated absorption spectra for multi-level atoms
    (Iop Publishing Ltd, 2006) Maguire, L. P.; van Bijnen, R. M. W.; Mese, E.; Scholten, R. E.
    We have developed a model for calculating saturated absorption spectra for dipole transitions in multi-level atoms. Using a semiclassical density matrix formalism, we derive a set of coupled differential equations for the internal state of the atom in a standing wave light field. The equations are solved using standard integration techniques. The absorption at each laser detuning is found from an average of the absorption for a number of velocities along the laser field, thermally weighted. The method is relatively efficient computationally yet quantitatively predicts important details of saturated absorption spectra including saturation, crossover resonances, merging of absorption lines at high intensity and optical pumping between hyperfine levels. We have measured saturated absorption and fluorescence spectra of 85Rb, and compare to our computational results for a 36-level model.