Nobuyuki Goto

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.

Hydrostatic Pressure Effects on the Triplet Relaxed Excited States of KI: Tl + -Type Phosphors through the Quadratic Jahn-Teller Interaction

Pressure effects on the emission spectra excited by the A absorption have been observed at various temperatures between 168 and 293 K in KI, KBr, and KCl doped with Tl + , In + , or Ga + . When both of the A T and A X bands appear, the A T band grows at the expense of the A X band as the pressure increases. Particularly, in KBr: Tl + and KBr: In + , the A X band disappears almost completely under 7.5 k bar. When only the A T band appears as in KCl: Tl + and KCl: In + , no drastic change has been observed up to 7.5 k bar. The pressure effects have been discussed on the basis of the quadratic Jahn-Teller effect by correlating the relaxed excited states for the A T and A X bands to the tetragonal and trigonal minima on the \(\varGamma_{4}^{-}\) (A) and \(\varGamma_{1}^{-}\) adiabatic potential energy surfaces respectively.

Dispersion Relation of Optical Eigen Modes in Chiral Smectic C by 4×4 Matrix Method

Dispersion relations of optical eigen modes (OEMs) in Sm C* are calculated by the 4×4 matrix method. The first order reflection region (full pitch band) consists of only a total reflection region. The structure of the second order reflection region, corresponding to that of the first order in cholesterics, strongly depends on the tilt angle of Sm C* and the propagation direction of OEMs. For a tilt angle smaller or larger than that of light propagation, the reflection region splits into three or consists of a single region with a structure.

Numerical Calculation of Ellipticities of Optical Eigen Modes in Cholesteric Liquid Crystals

The ellipticities of cholesteric optical eigen modes are numerically calculated using a 4×4 matrix method. In the limit of (pitch/wavelength)=0, the polarization states generally tend to be linear for light propagating at a finite angle to the helical axis, but circular for light propagating along the helical axis. The singularity of the latter case is discussed on the basis of the calculated results for infinitesimal obliqueness. The polarization state is nearly linear in the whole frequency range except in reflection regions when light propagates in a medium of small dielectric anisotropy at a large angle to the helical axis.

A Method for Studying Optical Eigen Modes in Cholesteric Liquid Crystals by Using Stress Plate Modulators in Tandem

An apparatus has been constructed for the direct study of the optical eigen modes (OEMs). The apparatus consists of an He–Ne laser, a linear polarizer (LP), a stress plate modulator (SPM), another SPM, another LP and a photomultiplier tube (PMT). A sample is placed between the SPMs, and the first combination of LP and SPM acts as a dynamic elliptical polarizer and the second one constitutes the analyzer which is always perpendicular to the polarizer. The output signal from the PMT is recorded in a transient memory and is accumulated and processed by a microcomputer. Taking the OEM propagating along the cholesteric helical axis as a test example, we calculated the temporal change in the PMT output signal; it indicates the existence of an ellipticity which gives zero transmittance. The calculated dependence of the ellipticity on wavelength agrees qualitatively with that of the true OEM, except for the region near or in the characteristic reflection. By performing actual measurement with a monodomain cholesteric film at a certain wavelength, we confirmed that the apparatus works well.

Line shapes in giant quantum attenuation of sound waves in bismuth

Abstract The giant quantum attenuation in semi-metals, which was predicted by Gurevich, Skobov, and Firsov, is affected by the deformation potential. In a strong magnetic field, the deformation potential strongly depends on the density of states. We have calculated the curves of attenuation coefficient in bismuth taking the density-of-states dependence of deformation potentials into account. The satisfactory result which quantitatively agrees with the experimentally observed line shapes of sound attenuation is obtained.

Electron-hole correlation in giant quantum attenuation of sound waves in Bismuth waves in bismuth

Abstract In a strong magnetic field, the deformation potential strongly depends on the density of states. Hence, there appears a strong correlation between the peaks as the peaks due to the electrons and holes come closer to each other. We made numerical calculations taking the density-of-states dependence of deformation potentials into account. The results could quantitatively explain the correlation shown by the experiments.

Dip and hump type quantum oscillations in magnetoacoustic attenuation in semimetals

In the strong magnetic field, the deformation potentials of semimetals themselves make the dip and hump type quantum oscillations due to the change of the densities of states so as to satisfy the charge neutrality condition. When the magnetic field is perpendicular to the propagation direction of the sound, the giant oscillations are smeared by the tilt effect and the change of deformation potentials alone is dominant. Therefore the dip and hump type quantum oscillations appear directly in the line shape of the attenuation of the sound in this configuration. This result accords with the experimental ones for Bi1-xSbx.