Recent experimental and theoretical results that link the phenomenon of dielectric relaxation in nematic liquid
crystals (NLCs) to their dynamics and fast electro-optical switching are presented. Namely, we illustrate that the
dielectric torque acting on the uniaxial nematic liquid crystal depends not only on the present value of the field and
the present orientation of the director, but also on the prehistory of these two parameters. The resulting "dielectric
memory" effect leads to a spectacular but counter-intuitive effect: director relaxation during the "switch-off" stage
can be accelerated if instead of the abrupt vertical back edge, one uses a voltage pulse with a non-instantaneously
vanishing back edge. The acceleration effect can be enhanced with a short high voltage pulse at the end of the
"switch on" process.
The dielectric dispersion in uniaxial nematic liquid crystals creates a "dielectric memory" effect whereby
the polarization induced by the electric field decays exponentially with time rather than instantaneously, as in
materials without dispersion. The induced polarization couples linearly with the electric field. This linear coupling
allows one to accelerate the director relaxation towards the "off" state by a specially designed electric pulse of a
proper polarity and duration We show theoretically and experimentally the possibility of electrically driving the
director towards the off state, thereby decreasing the switching time.
We show how a tightly focused laser beam can serve as a tool to image complex patterns of the director using the technique of fluorescence confocal polarizing microscopy (FCPM). We expand the capabilities of FCPM into the domain of real-time scanning in order to study the dynamic processes at the time scale of about 1ms. In this approach
which we call Fast FCPM, confocal imaging is performed using a modified Nipkow-disc scanning confocal microscope. In the Fast FCPM set up, we use a twisted nematic cell as a fast achromatic polarization rotator to change the polarization of probing light by 90°. The achromatic polarization rotator switches between two orthogonal polarization states when a sufficiently strong electric field is applied to reorient the director structure from the twisted to the homeotropic state. Both FCPM and Fast FCPM employ the property of anisotropic media to align fluorescent dye molecules. When observation is performed in polarized light, the measured fluorescence signal is determined by orientation of the dye molecules. As the dye molecules are aligned by the liquid crystal, the detected fluorescence signal visualizes the spatial patterns of the director rather than concentration gradients of dyes. Finally, we present 3D patterns of director associated with both static and dynamic processes in liquid crystals, anisotropic emulsions, and colloidal suspensions.