Showing papers by "Sophie Brasselet published in 2004"

Enhanced Second-Harmonic Generation by Metal Surfaces with Nanoscale Roughness: Nanoscale Dephasing, Depolarization, and Correlations

Abstract: On the basis of spectral-expansion Green's function theory, we theoretically describe the topography, polarization, and spatial-coherence properties of the second-harmonic (SH) local fields at rough metal surfaces. The spatial distributions of the fundamental frequency and SH local fields are very different, with highly enhanced hot spots of the SH. The spatial correlation functions of the amplitude, phase, and direction of the SH polarization all show spatial decay on the nanoscale in the wide range of the metal fill factors. This implies that SH radiation collected from even nanometer-scale areas is strongly depolarized and dephased, i.e., has the nature of hyper-Rayleigh scattering, in agreement with recent experiments. The present theory is applicable to nanometer-scale nonlinear-optical illumination, probing, and modification.

In situ diagnostics of the crystalline nature of single organic nanocrystals by nonlinear microscopy.

Abstract: We elucidate the crystalline nature and the three-dimensional orientation of isolated organic nanocrystals embedded in a sol-gel matrix, using a polarized nonlinear microscopy technique that combines two-photon fluorescence and second harmonic generation. This technique allows the distinction between monocrystalline structures and nanoscale polycrystalline aggregates responsible for incoherent second harmonic signals.

All-optical orientation of photoisomerizable octupolar zinc(II) complexes in polymer films.

Abstract: A new type of 4,4'-bis(styryl)-2,2'-bipyridine functionalized by a dialkylamino-azobenzene group has been prepared. This ligand has allowed the preparation of photoisomerizable octupolar tris(bipyridyl)zinc(II) complexes and the corresponding star-shaped polymer by atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). The photoisomerization properties of such new metallo-chromophores have been studied. The macroscopic molecular orientation of the corresponding doped and grafted NLO-polymer films is reported for the first time.

Coherent control of the optical nonlinear and luminescence anisotropies in molecular thin films by multiphoton excitations.

Abstract: Photoinduced orientational distributions are implemented with one- and two-photon absorption interference in polymer films containing chromophores that exhibit luminescent and nonlinear properties. The odd- and even-order parameters of the final distribution are probed by simultaneous measurement of second-harmonic generation (SHG) and two-photon fluorescence (TPF). We show the possibility of engineering local SHG and TPF anisotropies by controlling the polarization states and intensities of the writing optical fields. Complex multipolar orders are modeled with an irreducible spherical tensor-based formalism jointly applied to the molecular polarizabilities and field tensors.

Enhanced second harmonic generation by nanorough surfaces: nanoscale depolarization, dephasing, correlations, and giant fluctuations

Abstract: On the basis of spectral-expansion Green’s function theory, we theoretically describe the topography, polarization, and spatial-coherence properties of the second-harmonic (SH) local fields at rough metal surfaces. The spatial distributions of the fundamental-frequency and SH local fields are very different, with highly-enhanced hot spots of the SH. The spatial correlation functions of the amplitude, phase, and direction of the SH polarization all show spatial decay on the nanoscale in the wide range of the metal fill factors. This implies that SH radiation collected from even nanometer-scale areas is strongly depolarized and dephased, i.e., has the nature of hyper- Rayleigh scattering, in agreement with recent experiments. The present theory is applicable to nanometer-scale nonlinear-optical illumination, probing, and modification.

Advances in polymer based photonics technology: microlasers, electrooptic devices, new concepts

Abstract: The emergence of molecular photonics as a new domain of research at the cross-road of physics, chemistry and device engineering is being triggered by the increasing demands of broadband telecommunication systems which start to challenge the fundamental limits of current inorganic semiconductor based technologies. Increasing to 100 GHz and beyond the bandwidth acceptance of optoelectronic devices, such as modulators and switches, or down-scaling device dimensions into the new frontier of quantum physics have become scientific as well as industrially relevant targets, unlikely to be met by unimaginative extrapolation of current avenues. Facing this formidable challenge, the so-far relatively untapped wealth of molecular structures, and the targeted exploitation of their functional as well as structural flexibility throughout consistent molecular, material and device engineering steps, open-up thoroughly renewed horizons. An important asset is the complementarity and technological compatibility of polymer and inorganic semiconductor structures providing the possibility of smooth and economically viable transitions towards hybrid organic-inorganic technological solutions. Major current and foreseeable impacts appear to be in the realm of nonlinear optics (harmonic generation and carrier frequency shifting, routing, electrooptic modulation and switching, pulse shaping and synchronization, nonlinear refraction) and microlasers which will be exemplified by a selection of recent and ongoing developments in our laboratory at different macroscopic, microscopic and nanoscopic scales.

Nanoscale molecular nonlinear optics

Abstract: Nonlinear effects down to the nanoscale are investigated using nonlinear microscopy in poled polymer films, organic nanocrystals and nanoparticles, revealing local molecular organization and nanoscale interaction effects in between particles