Self-organized ensembles of nematic domains in magnetic and electric fields

The structural and magneto- and electro-optical properties of a self-organized ensemble of nematic domains formed on a polycarbonate film in the presence of a residual solvent are studied. The film covered one of the plane-parallel glass plates of a liquid crystal cell. The magnetic field stabilizing the planar alignment of the liquid crystal was applied parallel to the cell surfaces and the reorienting electric field, perpendicular to them. The voltage dependences of the intensity of light transmitted through the domain ensemble were obtained at different constant values of the magnetic field. The comparison of the experimental dependences with the dependences calculated using the liquid crystal free-energy minimization procedure has shown good agreement between them. The mutual effect of structural elements of the ensemble and the effects of phase modulation of light are analyzed by comparing the structural, magnetic, and electric coherence lengths.

Figure 1

Ensemble of 5CB domains formed on a PC film in the presence of a residual solvent: (a) texture observed between crossed microscope polarizers, (b) structure on the film surface at $z=0$, (c) structure at the distance $z<\xi$, and (d) uniform alignment of an LC at $z>\xi$.

Figure 2

Schematic of the propagation of laser radiation L through the SEND in cell C located between the N-S poles of an electromagnet. $U$ is the voltage on the cell, $d$ is the thickness of the LC layer, $\xi$ is the structural coherence length, $\psi$ is the angle between the polarization planes, and $\delta$ is the phase difference between the $o$ and $e$ waves, respectively.

Figure 3

Experimental (1–7) and calculated $(1^{\prime }$–$7^{\prime })$ dependences on light intensity $I$ on time $t$ and voltage $U$ obtained in the processes of the SEND formation $I_1$–$I_2$ (the left-hand and upper axes) and LC reorientation $I_2$–$I_7$ under the action of voltage $U$ in magnetic fields of $H$= (0, 0.4, 0.8, 1.2, 1.6, 2.15)$\times {10}^6{\mathrm{Am}}^{-1}$ (the left-hand and lower axes). Inset: initial part of the $I\left(U\right)$ dependence at $H=0$.

Figure 4

Dependences of “a” the structural coherence lengths $\xi$ on time $t$ during the domain growth (the right-hand and upper axes) and “b” of the initial values $I_2$–$I_7$ of the light intensity $I$ without voltage $U$ on the magnetic coherent length ${\xi }_H$ (the left-hand and lower axes).

Figure 5

LC domains on the PC film. (a) View of an individual growing domain between crossed microscope polarizers and domain structure; ${\mathbf{n}}_r$ and ${\mathbf{n}}_l$ are the director lines in the PR configuration, $r$ is the domain radius, and $w$ is the DL width. (b) Texture of an ensemble of domains with sharp walls.

Figure 6

Variation of the speckle arising during passage of laser radiation through the SEND under the action of a voltage of $U$= (a) 0, (b) 2.5, (c) 5, and (d) 80 V.