Valérie Véniard

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Silicon photonics meets the electronics requirement of increased speed and bandwidth with on-chip optical networks. All-optical data management requires nonlinear silicon photonics. In silicon only third-order optical nonlinearities are present owing to its crystalline inversion symmetry. Introducing a second-order nonlinearity into silicon photonics by(More)
We present a first-principles theory for the calculation of the macroscopic second-order susceptibility chi((2)), based on the time-dependent density-functional theory approach. Our method allows to include straightforwardly the many-body effects, such as crystal local fields and excitons. We apply the theory to the computation of the second-harmonic(More)
A major obstacle for computing optical spectra of solids is the lack of reliable approximations for capturing excitonic effects within time-dependent density functional theory. We show that the accurate prediction of strongly bound electron-hole pairs within this framework using simple approximations is still a challenge and that available promising results(More)
Dielectric screening of excitons in 2D semiconductors is known to be a highly non-local effect, which in reciprocal space translates to a strong dependence on momentum transfer q. We present an analytical model dielectric function, including the full non-linear q-dependency, which may be used as an alternative to more numerically taxing ab initio screening(More)
Two distinct interpretations have been proposed to account for conspicuous enhancements of the ionization peaks in the high energy part of above-threshold ionization spectra. One of them ascribes the enhancement to a multiphoton resonance involving an excited state, while other analysis performed for zero-range model potential link it to "channel closings,(More)
We address the question of the energy and angular distributions of the photoelectrons ejected from rare gas atoms submitted to ultra-intense infrared laser pulses, with peak intensities I(max) approximately 10(18) W/cm (2). Several unsolved issues regarding the angular distributions of the photoelectrons are analyzed. We believe that our results should help(More)
Starting from experimental findings and interface growth problems in Si/Ge superlattices, we have investigated through ab initio methods the concurrent and competitive behavior of strain and defects in the second-harmonic generation process. Interpreting the second-harmonic intensities as a function of the different nature and percentage of defects together(More)
With the help of a suitably chosen momentum-space analysis, we study some of the basic mechanisms governing the physics of the processes occurring when atoms are submitted to intense infrared laser pulses, with peak intensities 10(14) W cm(-2)</=I(max)</=10(15) W cm(-2). This intensity range is especially interesting because two highly nonlinear atomic(More)
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