1,721,031 research outputs found
Writing and Erasure of Holographic Gratings in Dye-Doped Polymer Dispersed Liquid Crystals
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Influence of the ions on the dynamical response of a nematic cell submitted to a DC voltage
No full textThe influence of the ions present in a liquid crystal on the dynamical response of a nematic slab submitted to a dc voltage is studied. The evolution of the system toward the equilibrium state is investigated by solving the continuity equation for the electric charge, taking into account the current of drift and of diffusion. Our analysis shows that the formation of the double layers close to the electrodes strongly modifies the distribution of the electric field across the sample. We evaluate the surface polarization due to the ions movements and the contribution to the anisotropic part of the surface energy having a dielectric origin. We show also that, even if the optical response of the liquid crystal is a slow phenomenon, the distribution of the ionic charge is rather fast. Consequently, the presence of the ions cannot be neglected in the determination of the flexoelectric coefficients when the nematic sample is submitted to a square wave having a period of the order of one second
Self phase modulation in nematic liquid crystal films: detailed measurements and theoretical calculations
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Self pulsing of the laser light transmitted by a nonlinear liquid-crystal interface near the phase transition
No full textSpectrograph Based on a Single Diffractive Element for Real- Time Measurement of Circular Dichroism
No full textIn this study, a novel and simple diffractive spectrographic method for
real-time measurements of circular dichroism (CD) is considered from a
theoretical and experimental approach. A demonstrator prototype of the
CD spectrograph has been developed and its performance has been
compared with a commercial phase-modulation CD spectrometer. The
main element of the device is a polarization holographic grating, recorded
in a thin photosensitive organic film, by two interfering opposite circularly
polarized beams. A peculiarity of this grating is that the amplitude of the
þ1 (1) order of diffraction is proportional to the right (left) circular
polarization component of the incoming beam. Here we demonstrate that
the CD spectrum of a specimen can be easily evaluated from the intensities
of the diffracted beams. A white light beam passing through the specimen
is diffracted from the grating and the intensities of the 6 1 orders of
diffraction are measured. Due to the spectral selectivity of the grating, the
CD at each wavelength can be evaluated at the same time using two linear
array detectors
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