Jeong Weon Wu

Broadband Cavity-Mode Lasing from Dye-Doped Nematic Liquid Crystals Sandwiched by Broadband Cholesteric Liquid Crystal Bragg Reflectors

[*] Prof. H. Takezoe, Dr. H. Choi, Dr. F. Araoka, Prof. K. Ishikawa Department of Organic and Polymeric Materials Tokyo Institute of Technology 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan) E-mail: takezoe.h.aa@m.titech.ac.jp Prof. J. W. Wu, J. Kim Department of Physics and Division of Nano Sciences Ewha Womans University Seoul 120-750 (Korea) E-mail: jwwu@ewha.ac.kr Dr. S. Nishimura, T. Toyooka Central Technical Research Laboratory Nippon Oil Corporation 8 Chidori-cho, Naka-ku, Yokohama 231-0815 (Japan)

Pulsed-laser electroholographic system using the interference fringe image of the CCD

In this study, it is newly attempted to combine digital holography method to get the holography fringe data using the CCD with the pulsed electro-holographic system for real-time display. Owing to the one-dimensional characteristic of the Bragg regime AOSLM that the fringe data propagating in parallel with the laser incident plane in the crystal cannot diffract the incident reference beam vertically by the momentum conservation, the diffraction of vertical direction from the AOSLM is impossible and the vertical parallax is not generated. Therefore the confocal lens system with a horizontal slit is introduced to obtain proper interference pattern. When the display of pulsed laser electro-holographic system is made by the fringe data of which bandwidth is reduced, the image clearness and quality is more improved than the recorded data without the confocal system with a horizontal slit since the fringe is formed to give mainly the horizontal parallax and the bandwidth of vertical direction is reduced so that the one line of object is projected onto only one line pixels of the CCD at same height.

Unique determination of the hyperpolarizability tensor ratio through a depolarized hyper-Rayleigh scattering under an external electric field

We analyzed the depolarized hyper-Rayleigh scattering from molecular system with a partial macroscopic polar ordering. It is shown that hyperpolarizability tensor ratio and molecular dipole moment can be determined simultaneously by the depolarization measurement as a function of the external field strength. As an experimental example, we performed a quantitative analysi sof the electric-field dependent depolarized hyper-Rayleigh signal from a poly-γ-benzyl-L-glutamate solution, obtaining the dipole moment and the ratio of hyperpolarizability components as 4.0 Debye and β311/β333=-0.81.

Nonlinear optical changes in 1D photonic bandgaps of cholesteric liquid crystal

A cholesteric liquid crystal cell was fabricated possessing 1-D photonic bandgap structure. From the measurement of the linear absorption spectrum of the cell, a bandgap was identified, centered at 1.08 eV (1143 nm) with the gap width of 0.1 eV (100 nm). Based on the linear absorption spectra, the dispersion of the principal refractive indices along the parallel and perpendicular directions of the molecule was determined as 1.631 and 1.476 at the wavelength of 1064 nm through Berreman matrix method. A Q-switched Nd:YAG laser (1064 nm) was employed to investigate the nonlinear optical changes of photonic bandgap. As the laser intensity was increased to 320 MW/cm2, the transmittance decreased from 0.51 to 0.47, corresponding to an 8% change. The nonlinear transmittance change was analyzed numerically by Berreman matrix method with the incorporation of Kerr nonlinearity in the optical response of the molecules forming cholesteric liquid crystal. The changes in the refractive indices along the parallel and perpendicular directions were 3.46 and 1.51 X 10-10 (cm2/W). The changes in the position and width of bandgap were 0.02 eV and 0.03 eV at the laser intensity of 320 MW/cm2.

Electrogyration effects in chiral nonlinear optical media

Summary form only given. Four examples of nonlinear optical effects are briefly described. The first of these is the presence of both the Pockels effect and optical activity in Bi/sub 12/SiO/sub 20/. As a second example, a polyisocyanate random copolymer containing an asymmetric chiral center and Disperse-Red-1 nonlinear optical chromophores is synthesized. Next, the induced chirality of a nonlinear optical chromophore and the chiral chitosan polymer complex is investigated for a potential candidate as a second order NLO material. Finally, a bent-shaped liquid crystal is introduced to study the electro-gyration effect.