Kenji Harada

Low-temperature fabrication of fine structures on glass using electrical nanoimprint and chemical etching

Periodic structures were imprinted on a soda lime glass surface below its glass transition temperature (Tg) using a carbon-coated SiO2 mold under application of DC voltage. The structure height increased with the applied DC voltage, although no significant increase with pressure was found. At a temperature around Tg, the height reached saturation. Chemical etching using 55% KOH solution at 70u2009°C increased the structure height to eight times the height before etching. Noticeable alternating depression patterns and rapid chemical etching are closely related with the selective decrease in sodium concentration, which occurred only in the surface areas that were pressurized by the mold.

Hologram replication technique in glass plates using corona charging

The authors propose a technique of recording in glass plates using corona charging. The recording material used in this study is conventional soda-lime glass. A surface-relief hologram on an azobenzene polymer film coated on a glass plate can be recorded as an electric charge distribution in the glass plate using corona charging. The hologram recorded in the glass plate can be reconstructed as a surface-relief structure on a fresh azobenzene polymer film coated on the glass plate, again using corona charging.

Holographic Recording on Azo-benzene Functionalized Polymer Film

Surface relief holograms are fabricated by irradiation of laser intensity pattern on the azo-benzene functionalized polymer films. The diffraction efficiency and the surface relief depth depend on the writing energy and the polarization of the laser beam. This structure is very stable at temperatures below the glass transition temperature Tg. The relief depth increases approximately ten times with the electric field by corona discharge at the temperature near Tg even if there is no recording laser light. On the other hand, the surface relief disappears keeping the film temperature near Tg, neither recording laser beam nor external electric field. Using this material as a holographic memory, we demonstrate some memory modes, such as write-once, erase, rewritable, overwrite and data holding, under the combination of recording laser beam, external electric field and film temperature.

Holographic Recording and Control of Diffraction Efficiency Using Photoinduced Surface Deformation on Azo-Polymer Films

Surface relief holograms were fabricated on azo-polymer films by the irradiation of interference laser fringes. The side-chain azo-polymer, poly-orange tom-1 isophoronediisocyanate, was used in this study. Recording characteristics of surface relief structures were investigated; they needed no post-treatment, and could be erased by heating or irradiating a uniform laser beam. The diffraction efficiency of the recorded hologram was markedly increased by corona charging. It was also controlled by irradiation of the laser beam (488 nm) with corona charging.

Recording Characteristics of Hologram in Glass Plate Using Corona Charging

We report on the recording characteristics of a hologram in a soda-lime glass plate. A surface relief holographic grating on an azobenzene polymer film coated on a glass plate is recorded in the glass plate using corona charging. The holographic grating recorded in the glass plate is directly read out. The first-order diffraction efficiency is 0.03% at a wavelength of 633 nm. The thermal, UV light, and water resistances of the hologram are also evaluated.

Poled Polymer Etalon Light Modulator on Integrated Circuits

Electrically addressed reflective spatial light modulators with polymeric thin films are fabricated on the surface of an n-type metal-oxide-semiconductor (NMOS) chip. The use of a resonator structure is proposed to minimize the driving voltage. The developed device is composed of 1×5 NMOS transistors and nonlinear polymeric materials sandwiched between aluminum electrodes. The electrooptical polymer consists of disperse red 1 (DR1)-doped poly-methyl-methacrylate (PMMA). Poling was demonstrated on this chip and the light modulation was observed using a lock-in amplifier. A modulation efficiency of 2.0 × 10-5 was obtained.

Generation of alkali-free and high-proton concentration layer in a soda lime glass using non-contact corona discharge

Formation mechanisms of alkali-free and high-proton concentration surfaces were investigated for a soda lime glass using a corona discharge treatment under an atmospheric pressure. Protons produced by high DC voltage around an anode needle electrode were incorporated into a sodium ion site in the anode side glass. The sodium ion was swept away to the cathode side as a charge carrier. Then it was discharged. The precipitated sodium was transformed to a Na2CO3 powder when the surface contacted with air. The sodium ion in the glass surface layer of the anode side was replaced completely by protons. The concentration of OH groups in the layer was balanced with the amount of excluded sodium ions. The substitution reaction of sodium ions with protons tends to be saturated according to a square root function of time. The alkali depletion layer formation rate was affected by the large difference in mobility between sodium ions and protons in the glass.

Temperature-dependent photoinduced third-harmonic-generation variation in azo-homopolymer and azo-doped polymer thin films

The temperature effect on the variation of photoinduced third-harmonic generation (THG) of an azo-polyurethane homopolymer and an azo guest–host polymer is studied at several different temperatures. At higher temperatures, both angular hole burning and molecule angular redistribution motions weaken, due to the decreases of cis-to-trans thermal relaxation time and the cis population and the increase of orientational diffusion coefficient. Smaller photoinduced THG variation is observed in both samples at higher temperatures. Results from the THG recovery experiment show that polyurethane homopolymer thin films pumped at a high temperature have the best photoinduced THG variation stability after turning off the pump beam.

Scintillation Characteristics and Radiation Damage of Ce-Doped Bi4Si3O12 Single Crystals.

We have analyzed the scintillation characteristics such as light yield and decay time and the radiation damage of Ce-doped Bi4Si3O12 (BSO) single crystals grown by the vertical Bridgman method. Ce was doped into BSO at 0.1, 0.2 and 0.4 at.% and the grown crystals were analyzed. For the Ce doping at 0.1 at.%, the light yield decreased by 40% while the average decay constant decreased by 20% (from 105 ns to 86 ns). Radiation damage was assessed by measuring the optical transmittance before and after irradiating the crystals with 60Co γ-rays for a maximum accumulated dose of 107 rad. Significant improvement was found for the radiation hardness of Ce-doped BSO.

Visual Cryptography Using Interference Color of High-Order Retarder Films

Visual cryptography is known as a method of sharing a secret image through several encrypted images. Conventional visual cryptography can display only monochrome images. We develop a multicolor visual encryption technique using the interference color of high-order retarder films. The encrypted films are composed of a polarizing film and retarder films. Retarder films exhibit an interference color upon sandwiching between two polarizing films. A prototype of a visual cryptography device using interference color is developed. Eight colors are represented by combining an encrypted image and a decoding mask composed of retarder films with various retardations.