Ryoichi Higuchi

Ultraviolet generation at 266 nm in a novel organic nonlinear optical crystal: l‐pyrrolidone‐2‐carboxylic acid

A novel organic nonlinear optical crystal, l‐pyrrolidone‐2‐carboxylic acid (l‐PCA), has been found to be phase matchable for second‐harmonic generation (SHG) and sum‐frequency mixing down to the UV range at room temperature. Tunable radiation down to 266 nm was obtained. The nonlinear coefficient d14 of l‐PCA for the fundamental wavelength of 532 nm was determined to be 0.32 pm/V. The angular acceptance (the full width at half‐maximum) of the type II phase‐matched SHG has also been measured to be 3.03 mrad cm which agreed with the calculated value. This value is much larger than that of the type I phase‐matched SHG in β‐BBO.

New Ferroelectric Liquid Crystals with Spontaneous Polarization Exceeding 10−7C/cm2 and Their Electrical and Optical Properties

Abstract New series of ferroelectric liquid crystals with neighbouring chiral carbons or a chiral carbon with C—CI binding next to the molecular dipole moment (C=O) are synthesized utilizing isoleucine, valine, leucine, amylalchol and 2-amino butanoic acid as starting materials and are found to possess extremely large spontaneous polarization exceeding 3 × 10−7C/cm2 and dielectric constants larger than 7000. These compounds are found to exhibit a novel dielectric behaviour such as hysteresis in the temperature dependence due to the strong molecular interaction with surfaces. The response of electro-optic elements prepared with these ferroelectric liquid crystals is found to be very fast, in the μsec range, even at room temperature.

Characteristics of Optical Switching and Memory Effects Utilizing Deformation of Helicoidal Structure of Ferroelectric Liquid Crystals with Large Spontaneous Polarization

The anomalous voltage-transmission hysteresis of ferroelectric liquid crystals associated with the unwinding and winding of a helicoidal structure was studied in detail. Utilizing this phenomenon in newly developed ferroelectric liquid crystals with an extremely large spontaneous polarization, it is indicated that a bistable switching and memory element with a reasonable working voltage and response time can be realized.

Dielectric properties of new stable ferroelectric liquid crystals with large spontaneous polarization

New series of ferroelectric liquid crystals with two chiral carbons or bulky molecular components at the chiral carbon are synthesized and are found to possess extremely large spontaneous polarization exceeding 2×10−7 C/cm2 and a dielectric constant larger than 7000. These compounds are stable and exhibit a novel dielectric behavior due to the large spontaneous polarization and strong interaction with surfaces.

Anomalous Dielectric Behaviour in Biphenyl Ester Series of Ferroelectric Liquid Crystals

In ferroelectric liquid crystals of biphenyl ester series with alkylcarbonyloxy (CnH2n+1COO) chain length n longer than 9 exhibit anomalous dielectric behaviour. The spontaneous polarization becomes 0, even in the chiral smectic-C phase, at around 30°C at which the reversal of the sign of the tilt angle is observed, indicating a change of the sign of the spontaneous polarization. The origin of this anomalous behaviour is also discussed in terms of molecular interactions.

NOVEL AMINO ACID CRYSTALS FOR PHASE-MATCHED SECOND-HARMONIC GENERATION : L-PYRROLIDONE-2-CARBOXYLIC ACID

A novel nonlinear optical amino acid derivative, L‐pyrrolidone‐2‐carboxylic acid (L‐PCA), has been studied for the application of UV generation by frequency upconversion of laser radiation. L‐PCA is relatively easy to grow from solution to a large size, typically ∼40×20×20 mm3, by a slow cooling method. This crystal is chemically stable because the crystal lattice is composed of a network of hydrogen‐bonded molecules. L‐PCA has a wide transparency extending to the UV region (the cutoff wavelength is 260 nm) and is therefore a good candidate for the second‐harmonic generation (SHG) of Nd:YAG laser radiation (1064 nm). The nonlinear‐optical coefficient d14 was measured to be 0.22 pm/V, and the measured phase‐matching angles agreed with values calculated using refractive index data. The effective nonlinear optical coefficient deff of the type‐I phase‐matched SHG has also been measured to be 0.20 pm/V. UV generation down to 266 nm was achieved by phase‐matched SHG in L‐PCA crystals.

Anomalous temperature dependence of the dielectric and optical properties in ferroelectric liquid crystals

Abstract The anomalous temperature dependence of the sign of the spontaneous polarization in a biphenyl ester series of ferroelectric liquid crystals is reported. The reversal of the sign of the spontaneous polarization in the chiral smectic C phase of 2MBNCBC ((S)-2′-methylbutyl-4′-n- nonylcarbonyloxy-(l,l′-biphenyl)-l-carboxylate) is observed at T m. This anomaly is studied in detail as functions of the length of the terminal alkyl chain, the applied electric field, the frequency and the applied hydrostatic pressure. T m has been confirmed to depend on the length of the terminal chain and the applied pressure. However, it is independent of the applied field and the measuring frequency. In the mixture of these compounds, this anomaly is also observed.

Bistability of Electro-Optic Effects in Ferroelectric Liquid Crystals

New type of bistable electro optic effects utilizing the transition between winding and unwinding states of helicoidal structure of the ferroelectric chiral smectic liquid crystals with large spontaneous polarization are studied. One effect uses the anomalous voltage-transmission hysteresis, and another effect uses the anomalous temperature-transmission hysteresis due to the balance between the forces of the chirality and the wall effect. In these effects the fast switching response is realized, and the special surface treatment and the optical polarizers are not required.

New Bistable Optical Switching Eletnent Utilizing Wound and Unwound States of Ferroelectric Liquid Crystal

A new type of bistable optical switching element utilizing differences of the scattering through the cell of ferroelectric liquid crystal in wound and unwound states has been established in 3M2CPOOB, in which both states can be stabilized due to the balance between the forces of the chirality and the wall effect.

Synthesis of new ferroelectric liquid crystals and their novel ferroelectricity

A new type of ferroelectric liquid crystal, the 4′-alkoxybiphenyl-4-yl (2S,3S)-3-methyl-2-halogenopentanoates, has been synthesized; these compounds possess novel ferroelectricity, with spontaneous polarization and dielectric constant larger than 10–7 C/cm2 and 6000, respectively.