Eiichi Kuze

Direct Method with Triangular Waves for Measuring Spontaneous Polarization in Ferroelectric Liquid Crystals

It is proposed to apply the direct measurement of spontaneous polarization using triangular waves to ferroelectric liquid crystals. The use of the triangular waves allows us to easily subtract the background contribution due to the conductive and the capacitive current and to accurately determine the spontaneous polarization, since a bump due to the polarization realignment appears on a straight base line. Moreover, the experiment with pulsed triangular waves clearly reveals no existence of the threshold voltage for deforming the helix and some characteristic properties of the dynamic reaction of the helix to the field applied.

On the methods of determining material constants in ferroelectric smectic C* liquid crystals

Abstract The methods to determine the material constants in ferroelectric Sm C* are summarized. The material constants dealt with are (1) the transition temperature, (2) the tilt angle, (3) the helical pitch, (4) the refractive index, (5) the spontaneous polarization, (6) the critical field to unwind the helix, (7) the elastic constant and (8) the viscosity coefficient. Based on the results obtained for 2-methylbutyl p-(p-n-alkoxybenzylideneamino) cinnamates (nOBAMBC), the importance of using properly prepared monodomain cells of high quality is emphasized by comparing our results obtained using the cells without surface treatment with others using the cells treated unidrectionally.

Experimental Studies on Reflection Spectra in Monodomain Cholesteric Liquid Crystal Cells : Total Reflection, Subsidiary Oscillation and Its Beat or Swell Structure

Many optical properties are presented here in the reflection spectra for monodomain cholesterics of various cell thicknesses at various angles of incidence. It is reported for the first time that left-circularly polarized light incident on a left-handed helix gives rise to a beat structure in the subsidiary oscillation, while right-circularly polarized light causes a swell to be superimposed on the subsidiary oscillation. The beat structure is ascribed to the excitation of two sets of optical eigen modes, each set consisting of two optical eigen modes of slightly different wavelength. The polarization characteristics of the total reflection band as well as the selective reflection band are also discussed.

A Practical Method of Preparing Thin Homogeneous Ferroelectric Smectic Cells for Electro-Optical Microsecond Switches: Alignment Control of Liquid Crystal Molecules by Utilizing Spacer Edges

A new method has been described for preparing a homogeneous monodomain cell with the non-treated clean surfaces. The method relies on the alignment control of liquid crystal molecules at the spacer edges and is particularly simple and convenient. The growing process and the resultant homogeneous monodomain have been shown for the parallel molecular alignment at the edge of a polyethylene terephthalate film cut along the main drawing direction. The possibility of the perpendicular alignment at the spacer edges has also been pointed out by observing that the molecules align perpendicularly at the interface to air.

Determination of Helical Pitch in Homeotropic Cell of Chiral Smectic C Liquid Crystal Using F-Center Laser

The selective reflection is observed in a monodomain homeotropic cell of chiral smectic C liquid crystal (DOBA MBC). In conjunction with the refractive index, the structural helical pitch is determined as a function of temperature. The results agree well with our previous results obtained by diffraction technique as well as optical microscope observation in a monodomain homogeneous cell. This agreement experimentally confirms that the fringe spacing observed under an optical microscope is ascribed to the full pitch. The large difference in the helical pitches determined by some investigators is also discussed.

Light Propagation in Williams Domains as Analyzed Numerically by Geometrical Optics

We have studied Williams Domain (WD) patterns in detail by observing tomograms with a polarizing optical microscope, confirming the following characteristic features: (1) there are two types of real images, upper and lower; (2) the spacings between the neighboring imaginary image lines are not uniform; and (3) when the focussing plane of the objective is moved above the upper real image or under the imaginary image, the sharp image line splits into two. By taking into account the ray deflection from the wave front normal as well as the focussing effect, we have calculated numerically the characteristic distribution of phase (optical path length) as well as intensity. The results can reproduce the tomograms observed here and the photographs taken by Sato et al. holographically, showing directly the optical path length as the interference fringe patterns.

Preparation of Monodomain Cells of Ferroelectric Liquid Crystals and Their Evaluation with an Optical Microscope

We have observed the growing process of high quality homogeneous cells directly in a high magnetic field by using a microscope with an elongated tube of 846 mm in length. For improving the cell quality, the application of the magnetic field is the most effective in comparison with other methods, such as the application of an electric field, SiO oblique evaporation, rubbing, etc. Factors affecting the cell quality were also studied by counting the number of characteristic defects that are always produced during the growing process. As expected, the cell quality is improved when the magnetic field is high, the cooling rate is low, the temperature control is accurate, the cell is thick, the sample is passed through the membrane filter and when the annealing time elapses. For the zone-refined sample, however, the cell quality is lowered unexpectedly; the reason for this is discussed.

Birefringence in the Sm A Phase and the Disappearance of Helicoidal Structure in the Sm C* Phase Caused by an Electric Field in DOBAMBC

To understand the exact nature of the Sm A-C* phase transition in the presence of an electric field E, we have studied in (S)-2-methylbutyl p-[(p-decyloxybenzylidene)-amino]-cinnamate (DOBAMBC) the field dependence of (1) critical temperature Tc (E) at which the helicoidal structure in the Sm C* phase disappears, (2) optical rotatory power ρ() along the effective optical axis in the Sm C* phase, and (3) birefringence Δn observed along the layer normal in the Sm A phase. The results obtained are: (1) Tc-Tc (E)∝E2±0.2, where Tc is the critical temperature for the Sm A-C* phase transition at zero field, (2) ρ() appears to stay almost constant when E is small, and (3) the birefringence is mainly due to the hindered rotation, but not to the tilt, of the molecules, and Δn∝|E| when T>(Tc+0.5)°C. These results are discussed in connection with the theoretical considerations by Michelson et al. and by Meyer et al.

Numerical Calculation of Optical Eigenmodes in Cholesteric Liquid Crystals by 4?4 Matrix Method

Light propagation in helical structures is formulated as an eigenvalue problem based on Berremans 4×4 matrix. Diagonalization of the secular equation is carried out to obtain the optical eigenmodes as a function of wavenumber and propagation direction relative to the helical axis, and sets of the optical eigenmodes are found to be classified into four types, whose appearance strongly depends on the wavenumber and the propagation direction. The selective and total reflections in cholesteric liquid crystals are characterized by the types of the eigenmodes for various angles of incidence.

A Practical Method of Preparing Thin Homogeneous Ferroelectric Smectic Cells for Electro-Optical Microsecond Switches (II): Sm A Liquid Crystal Growth under a Temperature Gradient

A large size homogeneous monodomain cell is prepared by growing smectic A under a temperature gradient. The nucleation of aligned smectic A is initiated with the aid of a spacer edge. The temperature gradient is obtained by using an ITO electrode properly etched as a local heater. The obtained monodomain size is at least one square millimeter.