Showing papers by "Sophie Brasselet published in 2005"

Encoding multipolar polarization patterns by optical poling in polymers: towards nonlinear optical memories

Abstract: We demonstrate spatially resolved polarization encoding of nonlinear information by all-optical poling of photoisomerizable and nonlinear molecules in polymer films. The second harmonic generation (SHG) polarization responses of the photo-induced patterns are imaged by a nonlinear microscope with 2µm lateral resolution. The strong SHG dependence to the poling fields polarizations is applied to information encoding, with a potential in high density optical data storage. In addition, the imprinted local nonlinear susceptibilities of multipolar symmetries cannot be deciphered by more traditional one-photon holography techniques.

Matching molecular and optical multipoles in photoisomerizable nonlinear systems

Abstract: We experimentally investigate the coupling rules between molecules and optical fields in the all-optical poling scheme. The efficiency and symmetry of the photoinduced quadratic nonlinearity is shown to be dependent on tensorial selection rules connecting the symmetries of the optical poling fields and the molecular tensors. We show that an optimal poling is obtained by matching the molecular symmetry to either a quasi-dipolar or a purely octupolar poling field, each being engineered by use of circular polarizations. Moreover, we define optimized poling conditions allowing the direct measurement of molecular nonlinear anisotropies. This research can be applied to nonlinear and photoisomerizable multipolar molecular systems.

Photo-induced rotation of single molecules

Abstract: We present the investigation of optically-induced rotation of single DCM (4-(dicyano methylene)-2-methyl-6-(p-dimethyl aminostyril)-4H-pyran) molecules in a low-T g polymer matrix. The rotation process is based on the photo-isomerization of the molecule occurring upon a resonant linearly polarized optical excitation. This pumping process creates a photo-selection angular cone, resulting in a motion of the molecular dipole perpendicularly to the linear excitation, stabilized by the polymer re-organization. Ensemble measurements are seen to be biased by the difficulty to discriminate between the re-orientation process and angular selective photo-bleaching. Such photo-bleaching effect can however be observed independently in single molecules data. The thermal rotational motion of single molecules in the polymer were first investigated, showing heterogeneous behaviors with orientational fluctuations of a about ten seconds time scale, due to the local viscosity and elasticity of the polymer environment. Under a linearly polarized pump at several hundreds of W/cm 2 intensity, a photo-induced orientation motion towards the perpendicular direction to the pump was observed for 50% of the molecules, within a typical time of a few tens of seconds. The remaining molecules showed orientational fluctuations dominating over the pump effect.