Personne :
Brasselet, Étienne.

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Brasselet
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Étienne.
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Université Laval. Département de physique
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Résultats de recherche

Voici les éléments 1 - 9 sur 9
  • Publication
    Accès libre
    Light-induced chaotic rotations in nematic liquid crystals
    (American Physical Society through the American Institute of Physics, 2006-02-23) Brasselet, Étienne.; Dubé, Louis J.
    Various nonlinear rotation regimes are observed in an optically excited nematic liquid-crystal film under boundary conditions for the light and material that are invariant by rotation. The excitation light is circularly polarized, the intensity profile is circularly symmetric, and the beam diameter at the sample location is a few times smaller than the cell thickness. A transition to chaos via quasiperiodicity is identified when the light intensity is taken as the control parameter. Transverse nonlocal effects are suggested to be the cause of the observed dynamics, and a simple model consisting of a collection of coupled rotators is developed to provide a qualitative explanation.
  • Publication
    Restreint
    Bifurcation analysis of optically induced dynamics in nematic liquid crystals : circular polarization at normal incidence
    (Optical Society of America, 2005-08-01) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Dmitry, Krimer; Kramer, Lorenz
    We present a detailed bifurcation analysis of the nonlinear reorientation dynamics of a homeotropically aligned nematic liquid-crystal film excited by an elliptically polarized beam at normal incidence with the intensity and the polarization state of light as the control parameters. The asymmetry arising from the elliptical polarization of the excitation lightwave is shown to affect dramatically the dynamics, and various new dynamical behaviors are reported: (i) quasi-periodic rotations for almost circular polarization; (ii) a discontinuous transition, identified as a homoclinic bifurcation, to a largely reoriented state over a large range of ellipticity values; (iii) oscillations associated with large reorientation; and (iv) optical multistability between several distinct dynamical regimes.
  • Publication
    Restreint
    Dynamics of light induced reorientation of nematic liquid crystals in spatially confined beams
    (Gordon and Breach, 2010-10-18) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.
    Optically induced reorientation dynamics in a nematic liquid crystal is investigated for circularly polarized laser beams with spot sizes smaller than the sample thickness. Various dynamical regimes, such as periodic, quasi-periodic, intermittent, self-organized and possibly chaotic regimes are observed. The role finite beam size is identified and a qualitative interpretation based on the spatial walk-off of the ordinary and extraordinary beams arising from double refraction phenomenon is proposed.
  • Publication
    Restreint
    Chaotic rotations generated by light in nematic liquid crystals
    (Gordon and Breach, 2006-09-22) Brasselet, Étienne.; Dubé, Louis J.
    Various nonlinear rotation regimes are observed in an optically excited nematic liquid crystal film under boundary conditions (for the light and the material) that are invariant by rotation. Th excitation light is circularly polarized, the intensity profile is circularly symmetric and the beam diameter at the sample location is a few times smaller than the cell thickness. A transition to chaos via quasiperiodicity is identified when the light intensity is taken as the control parameter. Transverse nonlocal effects are suggested to be the cause of the observed dynamics and a simple model consisting of a collection of coupled rotators is developed to provide a qualitative explanation.
  • Publication
    Accès libre
    Optically induced dynamics in nematic liquid crystals : the role of finite beam size
    (American Physical Society, 2004-02-10) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, Bernard
    We report on the influence of a finite beam size on the molecular reorientation dynamics when a nematic liquid crystal film is excited by a laser beam. We present experimental evidence of a new class of nonlinear dynamics when the excitation is a Gaussian shaped, circularly polarized laser beam at normal incidence. Various nonlinear regimes, periodic, quasiperiodic, intermittent, and possibly chaotic, are observed. A physical interpretation based on walk-off effects is proposed and its implications on current research in the field are discussed
  • Publication
    Restreint
    Transverse nonlocal effects in optical reorientation of nematic liquid crystals
    (Optical Society of America, 2006-01-01) Brasselet, Étienne.; Lherbier, Aurélien; Dubé, Louis J.
    We reexamine the optical reorientation of a homeotropic nematic-liquid-crystal film under finite beam-size excitation and linear polarization. We study the case of normal and oblique incidence (extraordinary wave). Under the most basic assumptions (geometrical optics approximation, elastic isotropy) we systematically analyze the dependence of transverse nonlocal effects as a function of the angle of incidence, the beam size, and the intensity. Besides recovering some well-known results (Fréedericksz transition threshold and spatial extension of the molecular reorientation as a function of the beam size), we identify a series of nonmonotonous behaviors of the material response as well as shape variations of the reorientation profiles.
  • Publication
    Restreint
    New laser induced spatio–temporal transition in nematics
    (Elsevier Science, 2002-05-07) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, Bernard
    We report the observation of a new light-induced spatio–temporal transition in homeotropically aligned nematic liquid crystals under the action of circularly polarized light. We believe that the competition of symmetric and asymmetric excitation modes is at the origin of this abrupt transition. A theoretical model explaining the main features of the observation is proposed
  • Publication
    Accès libre
    Optically induced dynamics in nematic liquid crystals : the role of twist deformation and asymmetry
    (American Physical Society, 2003-03-26) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, Bernard
    We present a theoretical study of optically induced dynamics in a homeotropic nematic liquid crystal excited at normal incidence. By retaining the first symmetric and antisymmetric reorientation modes, the dynamical equations are reduced to a four-dimensional problem. The main advantage of this minimal approach is to emphasize the role of twisted mode and asymmetry of the light-induced molecular reorientation in a manner suitable for a clear physical interpretation. Theoretical results are compared with experiments in the particular case of circularly polarized light beams to show the physical origin of mode competition and of the breakdown of chiral and longitudinal symmetry. The model successfully describes previous experimental studies such as time-dependent three-dimensional molecular dynamics, light-induced stabilized helical reorientation, and in-plane precession regime in achiral nematics. While a recent experiment has revealed a new spatiotemporal transition, the model succeeds to describe all the features of such a bifurcation pointing out anew the importance of asymmetry. Finally, the first quantitative description of the appearance of a giant mirrorless optical bistability when twisted reorientation modes are excited is demonstrated. A qualitative physical interpretation is suggested for all these phenomen
  • Publication
    Restreint
    Bifurcation analysis of optically induced dynamics in nematic liquid crystals : elliptical polarization at normal incidence
    (Optical Society of America, 2005-08-01) Krimer, Dmitry; Brasselet, Étienne.; Kramer, Lorenz; Galstian, Tigran; Dubé, Louis J.
    We present a detailed bifurcation analysis of the nonlinear reorientation dynamics of a homeotropically aligned nematic liquid-crystal film excited by an elliptically polarized beam at normal incidence with the intensity and the polarization state of light as the control parameters. The asymmetry arising from the elliptical polarization of the excitation lightwave is shown to affect dramatically the dynamics, and various new dynamical behaviors are reported: (i) quasi-periodic rotations for almost circular polarization; (ii) a discontinuous transition, identified as a homoclinic bifurcation, to a largely reoriented state over a large range of ellipticity values; (iii) oscillations associated with large reorientation; and (iv) optical multistability between several distinct dynamical regimes.