Considering the practical applications of liquid-crystal microlasers, such as laser displays and opto-communication
devices, broadband tunablity and continuous wave (cw) operation are strongly desired. Especially for the later one,
nobody has succeeded yet. For the cw operation, two problems must be solved: (1) Development of new dyes which are
stable against heat and light; (2) Development of novel cavities with high Q which makes the lasing threshold lower.
Here in this paper, we will introduce our recent researches mainly aiming at reduction of the lasing threshold in liquid
crystal microlasers; (1) single-output window devices; (2) multilayered devices; (3) use of a polymer dye improving
order parameter; (4) a new laser dye specially designed for dye-doped CLC lasers.
In this paper, we demonstrate two types of optically isotropic liquid crystalline states; (1) nano-segregated droplets of a
nematic liquid crystal, dispersed in a photo-crosslinked polymer matrix, and (2) BPIII with a very short pitch of the UV
region using bent-core nematogens with chiral-dopant. In both cases, we realize a complete dark state (OFF-state),
switchable to ON-state by applying an electric field. These optically isotropic states are expectable as a principle for
applications to extremely high-contrast and highly-responsive liquid crystal displays.
We have measured the terahertz (THz) absorption spectra of MBBA (4-Methoxybenzylidene-4'-n-butylaniline) and its
homologues by using THz time-domain and polarized fourier transform far-infrared (FT-IR) spectroscopy, and observed
the absorption peak due to the permanent dipole moments perpendicular to the molecular long axis. In addition, we also
measured the THz absorption spectra of CCN47 (4'-trans-butyl-4-cyano-4-trans-heptyl-1,1'-bicyclohexane) which has a
large permanent moment perpendicular to the long axis, by using polarized far-infrared FT-IR spectroscopy. The relation
between the vibration modes and the absorption in the THz region is discussed.
We describe a distinct polar nematic liquid crystal formed from the polar rod-like aromatic polyester which comprises 4-hydroxybenzoaic acid (HBA) and 6-hydroxy-2naphthoic acid (HNA) in a molar ratio of 73/27. The nemtic liquid crystal is biaxial and the polarity appears along both axes as determined by measurements of the second harmonic generation. The polar structure disappeasrs when the molecular weight in polyester is decreased, showing that the large dipole moment of each chain is responsible for the polar ordering. The strong dipole-dipole interaction between polar rod-like molecules may be ascribed to the origin of the polarility.
We have studied the lasing characteristics from a dye-doped nematic layer sandwiched by two polymeric cholesteric liquid crystal (PCLC) films as photonic band gap materials. The nematic layer possessing birefringence brings about the following remarkable optical characteristics; (1) reflectance in the photonic band gap (PBG) region exceeds 50% due to the retardation effect, being unpredictable from a single CLC film, (2) efficient lasing occurs either at the notch of PBG or at the photonic band edge, (3) the lasing emisions contain both right- and left-circular polarizations, and (4) tunable lasing can be achieved by the reorientation of nematic liquid crystal molecule under the application of an electric field.
Remarkable enhancement of second-harmonic (SH) generation in a ferroelectric liquid crystal was theoretically studied. The enhancement occurs when SH wavelength coincides with the wavelength at odd-number-th dips of subsidiary oscillation in one edge of the selective reflection band. To interpret this behavior, the electric field of inhomogeneous and homogeneous SH light in a cell was simulated for a right-handed (R) ferroelectric liquid crystal. It was found that R-circularly polarized light forms a standing wave inside the cell at the odd-number-th dips, when two counter-propagating beams with the same polarization (e.g., R-R) are incident. On the other hand, inhomogeneous and homogeneous waves are out of phase to each other at the bounding surface at the even-number-th dips, so that no enhancement occurs. As for an incidence of R- and L-polarized light, enhanced SH light is generated only toward the R-incidence side. The SH light is L-polarized in this case, while R-polarized SHG is observed from both sides for the incidence of counterwaves with the same polarization.
V-shaped switching in the smectic-C* like phase of a three- component mixture has been studied from the viewpoint of surface behavior. Two alignment layers, polyvinylalcohol (PVA) and polyimide (PI), were used to study the effect of alignment layer. Electro-optic, switching current and dielectric measurements were conducted using cells with various cell thicknesses. The PI cells exhibit V-shaped switching, though the PVA cells show bistable switching, clearly indicating the importance of alignment layer to realize V-shaped switching. The specialty of the three-component mixture was confirmed in the cell thickness dependence of the dielectric strength (Delta) (epsilon) and the relaxation time (tau) r. Namely, (Delta) (epsilon) and (tau) r show linear dependences on the cell thickness and does not saturate even in 50 micrometer cells, which are quite different from those in conventional ferroelectric liquid crystals. Attenuated total internal reflection ellipsometry was made to evaluate the molecular orientation and switching behavior near the surfaces. It was found that the orientation and the switching characteristics are almost the same as in the bulk, i.e., (1) molecules are aligned along the layer normal at 0 V, which is deviated from the rubbing direction by about 10 degrees, and (2) switching occurs collectively without threshold.
We measured the first and the higher order Bragg peaks corresponding to the layer thickness in the SmC and SmCA phases by X-ray diffraction, and calculated the smectic order parameters of the two phases. We found that the smectic layer in the SmCA phase is much more ordered than that in the SmC phase.
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