69 research outputs found
Coherent acoustic vibration of metal nanoshells
Using time-resolved pump-probe spectroscopy we have performed the first
investigation of the vibrational modes of gold nanoshells. The fundamental
isotropic mode launched by a femtosecond pump pulse manifests itself in a
pronounced time-domain modulation of the differential transmission probed at
the frequency of nanoshell surface plasmon resonance. The modulation amplitude
is significantly stronger and the period is longer than in a gold nanoparticle
of the same overall size, in agreement with theoretical calculations. This
distinct acoustical signature of nanoshells provides a new and efficient method
for identifying these versatile nanostructures and for studying their
mechanical and structural properties.Comment: 5 pages, 3 figure
Exceptionally Slow Rise in Differential Reflectivity Spectra of Excitons in GaN: Effect of Excitation-induced Dephasing
Femtosecond pump-probe (PP) differential reflectivity spectroscopy (DRS) and
four-wave mixing (FWM) experiments were performed simultaneously to study the
initial temporal dynamics of the exciton line-shapes in GaN epilayers. Beats
between the A-B excitons were found \textit{only for positive time delay} in
both PP and FWM experiments. The rise time at negative time delay for the
differential reflection spectra was much slower than the FWM signal or PP
differential transmission spectroscopy (DTS) at the exciton resonance. A
numerical solution of a six band semiconductor Bloch equation model including
nonlinearities at the Hartree-Fock level shows that this slow rise in the DRS
results from excitation induced dephasing (EID), that is, the strong density
dependence of the dephasing time which changes with the laser excitation
energy.Comment: 8 figure
Estimation du Modele de Croissance Neoclassique et Test de ses Proprietes Cycliques sur Donnees Francaises.
cycles economiques ; croissance economique
Hot Carriers in Semiconductors
ultrafast, GaAs, hole, ..................................................................................................................................... ............ ............ ............. ......
The R.B.C. Model Through Statistical Inference an Application on French Data.
statistics ; mathematics ; cycles economiques
Femtosecond investigation of the non-instantaneous third-order nonlinear suceptibility in liquids and glasses
The symmetry of the noninstantaneous Kerr susceptibility is investigated in different liquids and glasses using a time-resolved two-beam energy transfer technique with pulses in the 100–15 fs range. The pulse duration dependence of the ratio of the isotropic to anisotropic tensor elements is demonstrated in liquid CS2 and in silica, showing that the elementary mechanisms mediating the observed optical beam energy transfers are modified for short pulses. This effect is ascribed to alteration of the nuclear contribution and increasing influence of the electronic one
La methode des moments generalisees et ses extensions , theory et applications en macroeconomie.
THEORIE ECONOMIQUE;MACROECONOMIE
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