Koichi Arishima

Refractive index changes in photochromic diarylethene derivatives in polymethylmethacrylate films

Abstract We investigated photochromism and the refractive index change Δn in polymethylmethacrylate (PMMA) films made using 16 compounds of 1,2-diarylethene derivatives. The derivatives were classified as maleic anhydride or hexafluorocyclopentene diarylethene in type according to their structure. In PMMA films, the photochromic reactivity of maleic anhydride diarylethene derivatives strongly depends on their substituent structure. On the contrary, the photochromism of hexafluorocyclopentene diarylethene derivatives is observed in PMMA films regardless of their substituent. We found that Δn increased in proportion to the absorbance charge increase. Moreover, both Δn and ΔA were also proportional to the concentrations of the photochromic compounds. We believe that both Δn and ΔA are related to changes in the molecular structure of 1,2-diarylethene derivatives. We fabricated one transparent PMMA film of each type. Each film contained a high concentration of dispersed diarylethene derivatives. The changes in refractive index and absorbance of the maleic anhydride diarylethene type saturated at more than 15 wt.%. However, the changes in the hexafluorocyclopentene diarylethene type with a long alkyl chain were in proportion to the concentrations of the compound, and we obtained the largest refractive index change (0.0018) yet reported for 1,2-diarylethene derivatives in transparent PMMA films.

Photorefractive Effect in a Polymer Molecularly Doped with Low-Molecular-Weight Compounds

The photorefractive effect is observed in poly (methylmethacrylate) molecularly doped with three types of low-molecular-weight compounds, carrier transport (CTM), carrier generation (CGM) and nonlinear optical (NLO) materials. With these materials as dopants, the polymer exhibits both photoconductivity and the electro-optic (EO) effect under DC electric fields. The EO coefficient r33 is found to be linearly dependent on applied fields because of the lower glass-transition temperature (T g). In two-beam coupling and diffraction measurements, refraction gratings are written in the polymer. A phase shift of 90° between a refraction grating and a fringe pattern with applied fields proves the existence of the photorefractive effect, which is distinguished from heating effects. A maximum diffraction efficiency η of 4×10-6 is obtained in the photorefractive polymers.

Temperature Dependence of PHB Hole Profiles in Polymer Matrices

The temperature dependences of irreversible hole decay for tetraphenylporphines / polymers as guest / host systems were investigated. The irreversible hole decay values depend on the chemical structure of matrix polymers. Irreversible hole decay is caused by the motion of polymer side chains or backbones of poly(alkyl methacrylate)s and polyethylene. Excellent hole retention is observed in the PMMA matrix, and is explained by the small, symmetrical structure of methyl groups. PnDMA shows hole decay profiles similar to those of PE. This result indicates that PnDMA forms microstructures that are similar to PE microstructures because of long methylene side chains.

Persistent Spectral Hole-Burning in Semi-Crystalline Matrices Doped with Tetraphenylporphine

We report persistent spectral hole-burning (PSHB) in semi-crystalline polymer matrices doped with tetraphenylporphine (TPP). The host matrices were polyethylene (PE) and butadiene rubber (BR). The holewidth in TPP/PE was smaller than that observed in poly (methyl methacrylate) (PMMA) doped with TPP at about 5.5 K. However, the irreversible hole broadening measured with thermal cycling experiments was greater in PE. A similar tendency was also observed for the holewidth and irreversible hole broadening in semi-crystalline and amorphous BR matrices. These results show that the existence of the crystalline region plays an important role in the properties of spectral holes.

Defect detection in LiNbO3 crystals using cross Nicol optical system with heating function

LiNbO3 crystals are important for applications such as optical devices and surface acoustic wave filters. However, defects in such crystals can negatively affect device characteristics. Consequently, control of defects is important during device manufacturing. In this study, a new defect detection method using a cross Nicol optical system with a heating function and defect image enhancement is proposed. Experiments confirmed that defects detected by this method correspond to those imaged by X-ray topography. It was found that additional defects are formed by charge induced during heating.