Claude Sourisseau

General Maker-fringe ellipsometric analyses in multilayer nonlinear and linear anisotropic optical media

A general new 4(n+1)×4(n+1) matrix formulation of Maker fringes applicable to any anisotropic material containing n layers, convenient and straightforward for experimental data analyses, is proposed. The treatment of the transmitted and reflected harmonic waves includes the contribution of anisotropic one-photon absorption for the fundamental and harmonic waves under the assumption of no pump depletion and leads to a complete analysis of any linearly or elliptically polarized harmonic signal recorded under various incident polarization configurations. In the framework of the proposed model, we report detailed results of Maker fringes in various samples, for instance, in one and two z-cut quartz plates separated by a controlled air gap.

Isomérie de rotation et spectres de vibration du chlorure et du bromure d'allyle

Resume Les spectres infrarouges et Raman du chlorure et du bromure dallyle, sous differents etats physiques, ont ete etudies entre 3500 et30 cm −1 . Les isomeres de rotation cis et gauche sont nus en evidence et, grâce aux spectres infrarouges de letat vitreux a basse temperature, nous proposons une attribution des vibrations fondamentales observees pour les deux formes, en particulier des vibrations de torsion. La difference denthalpie des deux rotameres du chlorure dallyle est estimee par trois methodes differentes. Enfin les barrieres de potentiel de la torsion des deux composes sont discutees.

Photoinduced orientation in poly(vinylcinnamate) and poly(7-methacryloyloxycoumarin) thin films and the consequences on liquid crystal alignment

Thin films of poly(vinylcinnamate) and poly(7-methacryloyloxycoumarin) have been exposed to linearly polarized UV light. The resulting anisotropic films have been characterized by using UV, conventional and polarization modulation FTIR spectroscopies. In particular, several internal vibrational modes have been used as structural probes to examine the orientation of groups in the irradiated polymers. These experiments provide new information about the photoinduced anisotropy in these photocrosslinkable polymers upon irradiation with linearly polarized UV light, and an orientation mechanism is proposed. This mechanism is confirmed by studying the liquid crystal alignment induced by PVCi and poly(7-methacryloyloxycoumarin). Finally, the stability of the photoalignment process is discussed.

Photoinduced orientations of azobenzene chromophores in two distinct holographic diffraction gratings as studied by polarized Raman confocal microspectrometry

Optically isotropic thin films (0.5 μm) of an amorphous side-chain copolymer containing 10% azobenzene moieties and 90% meso-azobenzene groups (K1-10 sample) were irradiated by two interfering orthogonal (±45°) n or parallel (p + p) linearly polarized laser beams; permanent holographic diffraction gratings were thus inscribed. From atomic force microscopy (AFM) measurements, relatively weak amplitudes (about 50–60 nm) in the surface relief modulation (SRM) are detected but strong perturbations in the profiles and new substructures n are evidenced at half-period positions. Using a confocal microspectrometric technique we have n recorded various pre-resonance enhanced polarized Raman spectra from a large grating area and obtained spatially n resolved Raman images of the intensity variations. This yields new insight into the photoinduced orientation n effects, the angular distributions of the chromophore species, and finally the grating formation mechanisms. n Different theoretical equations of the polarized Raman scattering intensities, taking account of n the pump polarization directions and the high numerical aperture objective used, are derived. Then, an analysis of the experimental results allows us to extract values of the second 〈P2〉 and fourth 〈P4〉 coefficients in the n chromophore orientation functions at several positions of the SRM, in particular at the top and bottom regions, n and to calculate the corresponding normalized distribution functions ia information entropy theory. In both n gratings, somewhat broader distributions are found in the bottom regions, regions of greater polymer removal. n Thus, mass-transport phenomena have perturbed, to a weak extent in the (±45°) first case and to a larger n extent in the (p + p) second case, the primary photoinduced orientations. So, two simultaneous and superimposed n mechanisms appear to be responsible for the observed complex SRM in the highly birefringent K1-10 n copolymer under study and significant second-order contributions are suggested. The grating surface profiles n are thus reproduced by fitting the SRM amplitudes at the fundamental and doubled frequency and n the corresponding phase constant parameters: a n good agreement between the observed (AFM) and simulated profiles is obtained.

Molecular orientation and liquid crystal alignment properties of new cinnamate-based photocrosslinkable polymers

Isotropic thin films of three original phenyl substituted cinnamate-based polymers, here-after referred to as Para, Meta and Metamet have been exposed to linearly polarized UV light and their photoinduced molecular orientations have been studied. The resulting photocrosslinked anisotropic polymer films were characterized using UV, conventional and polarization modulation (PM) FTIR spectroscopies. From UV and PM-IR linear dichroism measurements, at least two simultaneous orientation processes appear to play a key role in these phenyl substituted cinnamate-based systems. On the one hand, isomerization reactions deplete chromophores along the polarization direction (P) of the UV light and induce a preferential orientation of remaining trans-isomers perpendicular to P; on the other hand, cycloaddition reactions lead to the formation of either head to head or head to tail photodimers aligned preferentially along P in the Para and to a lesser extent in the Meta and Metamet systems. These last results are related to the different liquid crystal alignment properties of the films, and the influences of the chemical structure of the chromophores are discussed.

Spectres infrarouges et structure des anions 2-methylallyle, CH3-C(CH2)2- et triméthylèneméthane, C(CH2)32−

Resume Les spectres infrarouges des composes solid es C 4 H 7 K et C 4 D 7 K ont ete etudies entre 4000 et 30 cm −1 . Une attribution complete des vibrations des anions C 4 H 7 − et C 4 D 7 − ainsi que des vibrations potassium-allyle est proposee et les constantes de force intramoleculaires sont calculees. De plus, lanion trimethylenemethane est identifie par spectrometrie infrarouge. Les structures des anions C 3 H 5 − , C 4 H 7 − et C(CH 2 ) 3 2− sont discutees et comparees a celles optimisees par la methode MINDO/3.

Chromophore orientation and the formation of surface reliefs in azobenzene side-chain polymers

The occurrence of surface relief gratings in azobenzene polymers under illumination with two superimposed laser beams is a puzzling effect which was discovered only few years ago. The origin of the large mass transport which occurs far below the glass transition temperature is not yet understood. We have performed experiments with cw holography. Due to low laser fluence, thermal effects can mostly be neglected. We have studied the relation between the light induced orientation of the chromophores in the bulk of the material and the observed surface relief gratings. We have performed a number of studies: Surface relief gratings were characterized under different polarization geometries of the writing beams, furthermore the grating period was varied. We could show that there is a competing behavior between the diffraction efficiencies by the volume grating and the surface relief, respectively. In order to analyze the orientational distribution function of the azobenzene chromophores, we have performed confocal Raman microspectroscopy in different regions of the surface relief grating. Our results are not in agreement with the current theories for the formation of surface reliefs.