Laser-induced reorientation effect and ripple structure in dye-doped liquid-crystal films

Photoinduced movement: how photoirradiation induced the movements of matter

Pioneered by the success on active transport of ions across membranes in 1980 using the regulation of the binding properties of crown ethers with covalently linked photoisomerizable units, extensive studies on the movements by using varied interactions between moving objects and environments have been reported. Photoinduced movements of various objects ranging from molecules, polymers to microscopic particles were discussed from the aspects of the driving for the movements, materials design to achieve the movements and systems design to see and to utilize the movements are summarized in this review.

Influence of methyl red as a dopant on the electrical properties and device performance of liquid crystals

The ionic effect in nematic liquid-crystal (LC) cells containing the azo dye methyl red was investigated by means of dielectric spectroscopy, measurements of voltage holding ratio (VHR) and ultraviolet/visible absorption spectroscopy. The experimental results indicated that incorporating a minute amount of the methyl red (< 0.03 wt%) in the LC host leads to the suppression of the ionic effect caused by impurity ions. Practically, the doped LC cells with a dye content of 0.02 wt% showed improved VHR and promoted lifetime by 15% and 180%, respectively, in virtually no expense of the optical transmittance.

Voltage-assisted photoaligning effect of an azo dye doped in a liquid crystal with negative dielectric anisotropy

We demonstrate a method of controlling the pretilt angle by field-assisted photoalignment in a vertically-aligned liquid crystal doped with a dichroic azo dye. By dynamically measuring both the pretilt angle and anisotropy in absorbance, we present detailed alignment variations in both the polar and azimuthal directions with the time of laser exposure that induces photoisomerization of the dye molecules. Significant differences in the resulting pretilt as well as optically-absorptive anisotropy are manifested between a regular photoalignment procedure and that in conjunction with a bias voltage during irradiation. It is found that the field-assisted exposure not only speeds up the photoalignment along the polarization direction of the laser beam but also leads to a higher orientational order.

Nonphotochemical laser-induced nucleation of nematic phase and alignment of nematic director from a supercooled thermotropic liquid crystal

A nonphotochemical laser-induced phase transition was studied in a supercooled 4;{'}-n -pentyl-4-cyanobiphenyl (5CB, also referred to as PCB and K15) liquid crystal, using linearly polarized 45 ps light pulses at a wavelength of 532 nm. The laser induced nucleation from the metastable supercooled isotropic phase to the nematic phase during slow cooling (0.001 degrees C/min) and high light intensity (3.9 MW/cm{2}) . The resulting nematic director tended to be aligned along the direction of the plane of polarization of the light. At the intensities used, there is no observable laser-induced realignment of the director once the sample is in the nematic phase, nor any permanent laser-induced ordering when the sample is illuminated only in the stable isotropic phase during slow cooling. These experimental results are consistent with a mechanism based on optical Kerr alignment.