Search results for "polarization."

Ferroelectric polarization switching induced from water adsorption in BaTiO 3 ultrathin films

2020

The influence of water on the out-of-plane polarization of ${\mathrm{BaTiO}}_{3}$ (BTO) ultrathin films is studied by means of density functional theory calculations. The adsorption is investigated for different coverages on both terminations of BTO with, for each case, all possible states of polarization, namely, paraelectric, polarized upward, and polarized downward. We thus demonstrate different behavior as a function of the termination. While ${\mathrm{H}}_{2}\mathrm{O}$ adsorbs only dissociatively on the BaO termination, with a reinforced interaction compared to BTO without out-of-plane polarization, only molecular adsorption is observed on the ${\mathrm{TiO}}_{2}$ termination. In addi…

About the role of hamiltonian singularities in controlled systems : applications in quantum mechanics and nonlinear optics

2012

This thesis has two goals: the first one is to improve the control techniques in quantum mechanics, and more specifically in NMR, by using the tools of geometric optimal control. The second one is the study of the influence of Hamiltonian singularities in controlled systems. The chapter about optimal control study three classical problems of NMR : the inversion problem, the influence of the radiation damping term, and the steady state technique. Then, we apply the geometric optimal control to the problem of the population transfert in a three levels quantum system to recover the STIRAP scheme.The two next chapters study Hamiltonian singularities. We show that they allow to control the polar…

Optical spectra beyond the amplifier bandwidth limitation in dispersion-managed mode-locked fiber lasers

2011

We investigate the intracavity pulse dynamics inside dispersionmanaged mode-locked fiber lasers, and show numerically that for a relatively wide range of parameters, pulse compression dynamics in the passive anomalous fiber can be accompanied by a significant enhancement of the spectral width by a factor close to 3. Varying the average cavity dispersion also reveals chaotic dynamics for certain dispersion ranges. The impact of the implementation of an optical output port to tap optimal pulse features is discussed. © 2011 Optical Society of America.

Can SSMF handle ULH 40-Gb/s WDM transmission?

2007

Structures optiques dissipatives en cavité laser à fibre

2011

This thesis presents a study of the nonlinear dissipative dynamics of localized of self organized structures in passively mode-locked fiber laser through nonlinear polarization evolution. We reveal the existence of a gradual transition from the quasi-cw to mode locked dynamics in the multi-pulsing regime. We emphasize on the intermediate state, where various new dynamics are observed. We study collective behaviors of dissipative solitons in the presence of a continuous background. One of the complex and attractive dynamics presented is the "soliton rain", which composed of three field components : continuous modes of background, drifting of solitons and condensed phase solitons. This dynami…

Molecular polarizability of Si/Ge/GaAs semiconductors clusters

2004

The interacting induced dipole polarization model implemented in our program for the calculation of molecular polarizabilities (POLAR) is used for the calculation of the molecular dipole-dipole polarizability ${\overline{\overline{α}}}$. POLAR is tested with Si$_{n}$, Ge$_{n}$ and Ga$_{n}$As$_{m}$ small clusters. The polarizability is an important quantity for the identification of clusters with different numbers of atoms and even for the separation of isomers. The results for the polarizability are in agreement with reference calculations performed with our version of the program PAPID (polarisabilites atomiques par interactions dipolaires) and with reference computations from Dr. J.R. Che…

Effect of size and deformation on polarizabilities of carbon nanotubes from atomic increments

2004

The interacting induced-dipole polarization model implemented in program POLAR is used for the calculation of the polarizability α. The method is tested with single-wall carbon nanotubes (SWNTs) as a function of radius and elliptical deformation. This work gives a partial success with the application of POLAR when compared with reference calculations performed with program PAPID. α follows a simple law. PAPID differentiates more effectively than POLAR among SWNTs with increasing radial deformation, a can be modified reversibly by external radial deformation. Different effective αeff are calculated for the atoms at the highest and lowest curvature sites. The difference between POLAR and PAPI…

Polarization Switching in Heterophase Nanostructures: PLZT Relaxor Ceramics

2005

The polarization switching is experimentally investigated in hot-pressed PLZT-x/65/35 ceramics with a lanthanum content from 5 to 12 at. %. The specific features in the temperature dependence of the polarization switching in a heterophase state are interpreted by analyzing the change in the switched charge measured over wide ranges of fields and temperatures. Particular emphasis is placed on the role of depolarization fields induced by interphase boundaries. A model of the evolution of polydomain nanostructures with a change in the temperature and in the response to an external field is considered. It is assumed that the low-temperature dielectric anomaly and the temperature hysteresis are …

Launching propagating surface plasmon polaritons by a single carbon nanotube dipolar emitter.

2011

International audience; We report on the excitation of propagating surface plasmon polaritons in thin metal films by a single emitter. Upon excitation in the visible regime, individual semiconducting single-walled carbon nanotubes are shown to act as directional near-infrared point dipole sources launching propagating surface plasmons mainly along the direction of the nanotube axis. Plasmon excitation and propagation is monitored in Fourier and real space by leakage radiation microscopy and is modeled by rigorous theoretical calculations. Coupling to plasmons almost completely reshapes the emission of nanotubes both spatially and with respect to polarization as compared to photoluminescence…

Strongly directional scattering from dielectric nanowires

2017

It has been experimentally demonstrated only recently that a simultaneous excitation of interfering electric and magnetic resonances can lead to uni-directional scattering of visible light in zero-dimensional dielectric nanoparticles. We show both theoretically and experimentally, that strongly anisotropic scattering also occurs in individual dielectric nanowires. The effect occurs even under either pure transverse electric or pure transverse magnetic polarized normal illumination. This allows for instance to toggle the scattering direction by a simple rotation of the incident polarization. Finally, we demonstrate that directional scattering is not limited to cylindrical cross-sections, but…