Solitons in Nonlocal Media

List of Figures
1.1 (a) In the isotropic phase the molecules are positioned without long
range order. (b) In nematics the molecules have no positional order, but
have an orientational order. The molecular mean axis at each point is
expressed by a vectorial field ˆn called director. . . . . . . . . . . . . . . 8
1.2 Typical dimensions of a 5CB molecule (a) and chemical structure (b). . 8
1.3 Spherical reference system. Axis z is directed as the director ˆn. . . . . . 9
1.4 (a) In absence of external electric fields the director lies on the plane yz,
forming an angle θ0 with ˆz. (b) When an electric field is applied parallel
to ˆy, a dipole is induced in the molecules, which rotates towards the
electric field in order to minimize their energy. The equilibrium angle
θ is reached when the total torque acting on molecules becomes null. I
note how rotations take place in a plane defined by the excitation geometry. 12
2.1 Sketch of the NLC sample: (a) side view, (b) top view, (c) front view.
Voltage at 1kHz is applied along x via two transparent electrodes de-
posited onto the glass slides that define the yz plane. ITO stands for
Indium Tin Oxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2 (a) Experimental set-up. (b) Input field E and its polarization in the
plane xy at z = 0. i.e. at the interface between air and NLC. Sign
convention is such that β shown in the figure is positive. . . . . . . . . . 17
2.3 Director ˆn and the two angles ξ and γ used to describe its orientation
in space. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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