Ab initio calculations of the optical properties of crystalline and liquid InSb

Ab initio calculations of the electronic and optical properties of InSb were performed for both the crystalline and liquid states. Two sets of atomic structure models for liquid InSb at 900 K were obtained by ab initio molecular dynamics simulations. To reduce the effect of structural peculiarities in the liquid models, an averaging of the two sets of the calculated electronic and optical properties corresponding to the two liquid models was performed. The calculated results indicate that, owing to the phase transition from crystal to liquid, the density of states around the Fermi level increases. As a result, the energy band gap opening near the Fermi level disappears. Consequently, the optical properties change from semiconductor to metallic behavior. Namely, owing to the melting of InSb, the interband transition peaks disappear and a Drude-like dispersion is observed in the optical dielectric functions. The optical absorption at a photon energy of 3.06 eV, which is used in Blu-ray Disc systems, increases owing to the melting of InSb. This increase in optical absorption is proposed to result from the increased optical transitions below 2 eV

Analysis of the Local Field near Au Nanowires by Optical Second Harmonic Spectroscopy

We have measured optical second harmonic (SH) intensity from Au nanowire arrays as a function of the photon energy. We have found that the SH response is weak when the electric field and the nanowire axes are perpendicular to each other, due to the canceling of the incident field by the depolarization field created by the dielectric response of the nanowires. This cancellation of the incident field is found to be weak when the incident photon energy exceeds 1.6eV due to the less ideal metallic response of Au.Analysis of the Local Field near Au Nanowires by Optical Second Harmonic Spectroscopy, Goro Mizutani / Akira Sugawara / Haruyuki Sano, Frontiers of Basic Science Towards New Physics Earth and Space Science Mathematics, Ed. Hideaki Takabe / Nguyen Hoang Luong / Yoshichika Onuki (Osaka University Press, Osaka, 2006/3) p. 163-164

First principles study of the electronic and optical properties of crystalline and liquid Sb_2Te_3: Phase-transition-induced changes in optical properties

To clarify the mechanism by which the optical properties of Sb_2Te_3 change because of its solid-liquid phase transition, we carried out ab initio calculations of the electronic and optical properties of Sb_2Te_3 in both the crystalline and liquid states. The calculated results indicate that the density of states around the Fermi level increases because of melting and that the energy bandgap observed in the crystalline state consequently disappears. The imaginary part of optical dielectric functions of crystalline Sb_2Te_3 has a large peak at a photon energy of ħω = 1.5 eV. When Sb_2Te_3 melts, it exhibits somewhat metallic optical properties and its optical absorption at ħω = 3.06 eV, which is used in Blu-ray Disc systems, decreases. This decrease in optical absorption is proposed to result from a large reduction of the optical transition strength at ħω ≈ 1.5 eV

Selective observation of starch in a water plant using optical sum frequency microscopy

The photosynthesis, transfer, and storage of starch are the most important biogenic processes occurring in plants. In order to observe the colorless and transparent starch granules in a plant, a chemical pretreatment such as staining of the starch is currently required, which seriously damages the tissue cells in the plant. In this study, it is demonstrated that non-destructive chemical analysis of starch granules in a plant can be performed by using optical second harmonic and sum frequency microscopy. This novel technique for in vivo analysis will provide epoch-making information about saccharides in a plant and can be extended to the analysis of many other materials, from living tissue to semiconductors

Optical Sum Frequency Generation Spectra of Water Molecules on a Polycarbonate Film Exposed to O_2 Plasma

We have performed sum frequency generation (SFG) spectroscopy of water molecules on a polycarbonate (PC) film with and without 1 minute O_2 plasma exposure. The intensity of SFG signal corresponding to the O-H stretch vibrations of water at a water/PC film interface was ～1000 times as low as that of signal from a water/quartz interface. In the SFG spectrum of water facing a pristine PC film, peaks at 3270 and 3440 cm^, and a shoulder at 3620 cm^ were observed. In the SFG spectrum of water on the film exposed to O_2 plasma, peaks were observed at 3200 and 3450 cm^. The peak at 3270 cm^ red-shifted to 3200 cm^ by the O_2 plasma exposure. The intensity of the peak at 3200 cm^ was higher than that at 3450 cm^. The shoulder at 3620 cm^ disappeared after the O_2 plasma exposure. The modulations of these peaks represent that the packing structure of water molecules was more ordered on the film after the O_2 plasma exposure

Sum Frequency Generation Confocal Microscopy Observation of a Fish Scale

An optical sum frequency generation (SFG) microscopy image of a fish scale of Pagrus major was observed. Its SFG spectra were also measured and were compared with that of collagen of Achilles tendon of a cow (Bos taurus). From this comparison, the peak near 2950 cm^ in the fish scale spectrum was assigned to the fish collagen. The two collagen spectra showed different line shapes and widths owing to a difference in the background nonlinearity. In the SFG image of the fish scale cross section, stronger signal was observed from the sea side than from the body side