Yukihito Nakazawa

Formation of dynamic holograms based on spatial modulation of molecular motions of ferroelectric liquid crystals

The formation of dynamic holograms based on the spatial modulation of the molecular motions of ferroelectric liquid crystals (FLCs) was demonstrated. The consecutive rotational switching motion of FLC molecules under an alternating electric field was modulated by the photoinduced additional electric field built at the interference fringe. This spatially periodic difference in molecular motions of an FLC was confirmed to work as a diffraction grating. Since the motion-mode hologram is stable and the response is very fast when compared to photorefractive polymers, the motion-mode hologram appears to be promising for various photonic applications.

Photorefractive Effect of Photoconductive-Polymer-Stabilized Ferroelectric Liquid Crystals

The photorefractive effect of photoconductive-polymer-stabilized ferroelectric liquid crystals (FLCs) was investigated. A photoconductive acrylate monomer and an electron acceptor compound were mixed with an FLC, and the mixtures were photopolymerized in the ferroelectric phase. A photoconductive polymer network was formed in the FLC medium, and a polymer-stabilized FLC was obtained. The photorefractive effect was evaluated by a two-beam coupling experiment. A large gain coefficient was obtained in the polymer-stabilized FLCs.

Photorefractive effect in composites of ferroelectric liquid crystal and photoconductive polymer

The photorefractive effect in composites of a ferroelectric liquid crystal (FLC) and several photoconductive polymers was investigated. The photorefractivity of mixtures of photoconductive polymers and an FLC (polymer/FLC), as well as that of photoconductive‐polymer‐stabilized ferroelectric liquid crystals (PPS‐FLCs) was examined. The polymer/FLC samples exhibited two‐beam coupling gain coefficients of about 6∼12 cm−1 in a 5 µm gap cell. The photopolymerization of a methacrylate monomer in the FLC medium established a polymer‐stabilized state in which the alignment of FLC molecules was mechanically stabilized. The noise in a two‐beam coupling signal was reduced significantly in the PPS‐FLC samples.

Photorefractive effect of polymer-stabilized ferroelectric liquid crystals

The photorefractive effect of polymer-stabilized ferroelectric liquid crystals (FLC) was investigated. Two-types of monomers, a liquid crystalline monomer and a photoconductive monomer, were mixed with an FLC and the mixtures were photopolymerized in the ferroelectric phase. The polymer-network was formed in the FLC medium and a polymer-stabilized FLC was obtained. The polymer-stabilized FLC exhibited monostable switching properties. The photorefractive effect was evaluated by a two-beam coupling experiment. It was found that the photorefractive effect was strongly dominated by the preparation condition of the polymer-stabilized FLCs. Large gain coefficients were obtained in the photoconductive-polymer-stabilized FLCs.

Photorefractive effect of ferroelectric liquid crystals (Invited Paper)

The photorefractivity of a ferroelectric liquid crystal (FLC) mixed with a photoconductive compound was investigated in detail. FLCs are anisotropic media, so that laser beam incidence conditions strongly affect the formation of the refractive index grating. Effects of intersection angles of the laser beams, sample angle and sample thickness on the photorefractivity of FLCs were examined. The motion-mode photorefractive efffect of a FLC was also investigated.

Spontaneous Polarization Reorientation Photorefractive Effect in Ferroelectric Liquid Crystals

The photorefractive effect of a series of low-molecular-weight ferroelectric liquid crystals (FLCs) doped with photoconductive compounds was investigated using two-beam coupling experiments. Asymmetric energy exchange was observed only in the ferroelectric phase, and the refractive index formation time was found to be ∼30 ms, which is faster than that of nematic photorefractive LCs. These results indicate that the mechanism of the photorefractive effect in FLCs is different from that in nematic LCs. The photorefractivity of a photoconductive polymer and FLC mixture was also investigated, and the effects of temperature, the strength of the applied electric field and spontaneous polarization on the diffraction efficiency were examined.

Spontaneous polarization reorientation photorefractive effect in low-molecular-weight ferroelectric liquid crystal mixtures

The photorefractive effect of 14 ferroelectric liquid crystals (FLCs) mixed with a photoconductive compound was investigated by two-beam coupling experiments. The influence of the properties of low-molecular-weight FLCs on the photorefractive iffect was examined, and it was found that the photorefractive two-beam coupling gain coefficients and the refractive index grating formation time are strongly dependent on the properties of FLCs. The effects of the magnitude of the spontaneous polarization, viscosity, and the homogeneity of the surface-stabilized state on the photorefractivities of FLCs are discussed based on these findings.

Spontaneous polarization reorientation photorefractive effect in ferroelectric liquid crystals

The photorefractive effect of a series of low-molecular-weight ferroelectric liquid crystals (FLCs) doped with photoconductive compounds was investigated using two-beam coupling experiments. Asymmetric energy exchange was observed only in the ferroelectric phase, and the refractive phase, and the refractive index formation time was found to be ~30 ms, which is faster than that of nematic photorefractive LCs. These results indicate that the mechanism of the photorefractive effect in FLCs is different from that in nematic LCs. The photorefractivity of a photoconductive polymer and FLC mixture was also investigated, and the effects of temperature, the strength of the applied electric field and spontaneous polarization on the diffraction efficiency were examined.