Power handling capability of dielectric-coated,metallic, hollow waveguides for CO2 laser light

A theoretical analysis has been carried out to evaluate the power handling capability of hollow waveguides for CO₂ laser light. Dielectric-coated metallic waveguides are shown to transmit much higher powers than conventional metallic waveguides.     

Measurements of mode field diameter and effective area of photonic crystal fibers by far-field scanning technique

We have demonstrated that the correction factor k _n = A _eff/(πw ²), where ω = MFD/2 (MFD: mode field diameter), is above 1.20 for photonic crystal fibers (PCFs) with structural parameters in the range of d/Λ ≅ 0.40 to 0.90 (d/Λ ratio of hole diameter d and pitch Λ). By using the far-field scanning (FFS) technique and the finite difference method, the results of experimental measurements and numerical simulations differed by only 0.9 to 3.0% for two types of PCFs. The finding that k _n ≠ 1.0 for PCFs indicates that their electrical field distribution is non-Gaussian and cannot be determined by assuming a conventional step-index distribution for PCFs. It was also found that the ITU-T Petermann II definition is the most suitable for MFD measurements of PCFs with non-Gaussian distribution.     

Study of γ d → π + π − d Reaction in an Energy Region of 0.67 ≤ E γ ≤ 1.08 GeV

Double charged pion photoproductions from the deuteron have been studied at Research Center for Electron Photon Science (ELPH), Tohoku University. Tagged photon beams in an energy range of 0.67 ≤ E _γ ≤ 1.08 GeV were impinged on the liquid deuteron target. Produced charged particles were observed with the Neutral Kaon Spectrometer2 (NKS2). The γ d → π ⁺ π ^? d process was clearly separated among the three charged tracks. We obtained the photon energy dependence of the normalized yields of this process.     

Study of Strangeness Photoproduction on the Neutron in the Threshold Region

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K ⁰ with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K ⁰ + Λ + p was estimated from the measured integral cross section of γ + d → Λ + X. The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K ₁, as ~ ?1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K ⁺ Λ.     

Basic [Au25(SCH2CH2Py)18]−⋅Na+ Clusters: Synthesis,Layered Crystallographic Arrangement,and Unique Surface Protonation

The synthesis of high‐purity and high‐yield Au₂₅ clusters protected by the basic pyridyl ethanethiol (HSCH₂CH₂Py, 4‐PyET and 2‐PyET) is presented. Single‐crystal X‐ray diffraction of the [Au₂₅(4‐PyET)₁₈]^??Na⁺ clusters has revealed a structure similar to that known for the phenyl ethanethiolate analogue, but with pyridyl‐N coordination to Na⁺, a more relaxed ligand shell, and a profoundly layered arrangement in the solid state. Because of the pendant Py moiety, the [Au₂₅(PyET)₁₈]^? clusters are endowed with unique (de)protonation equilibria, which has been characterized in detail by UV/Vis absorption and ¹H NMR spectroscopy. [Au₂₅(PyET)₁₈]^? clusters showed an unexpectedly H⁺‐dependent solubility that is tunable in aqueous and organic solvents. The successful synthesis of the basic Py‐terminated thiolate‐protected Au₂₅ clusters paves the way to realize a new family of metalloid clusters possessing basic properties.     

Hollow-fiber delivery of high-power pulsed Nd:YAG laser light

We propose hollow fibers for delivery of high-peak-power pulsed Nd:YAG laser light. Hollow fibers with an internal polymer layer were fabricated by a liquid-phase coating technique. We reduced the losses of the fibers in the near-infrared region by producing a silver film that was very smooth owing to use of an ultrasonic wave for mixing of the silver and the reducer solutions in the silver-plating process. The straight losses of the 1-m-long polymer-coated fibers were 0.3 dB for the 700-mum bore size and 0.1 dB for the 1000-mum bore fiber.     

Picolinoxy group, a new leaving group for anti SN2' selective allylic substitution with aryl anions based on Grignard reagents

The picolinoxy group was found to be an extremely powerful leaving group for allylic substitution with aryl nucleophiles derived from ArMgBr and CuBr*Me2S. The substitution proceeds with anti SN2' pathway and with high chirality transfer. The electron-withdrawing effect of the pyridyl group and chelation to MgBr2 are likely the origin of success. Results suggesting these effects were obtained.     

Amphiphilic molecular design as a rational strategy for tailoring bicontinuous electron donor and acceptor arrays: photoconductive liquid crystalline oligothiophene--C60 dyads

For tailoring solution-processable optoelectronic thin films, a rational strategy with amphiphilic molecular design is proposed. A donor-acceptor dyad consisting of an oligothiophene and C60, when modified with a hydrophilic wedge on one side and a paraffinic wedge on the other (1Amphi), forms over a wide temperature range a photoconducting smectic A liquid crystal having bicontinuous arrays of densely packed donor and acceptor units. In contrast, when modified with only paraffinic wedges (1Lipo), the dyad forms a smectic A liquid crystalline mesophase, which however is poorly conductive. As indicated by an absorption spectral feature along with a synchrotron radiation small-angle X-ray scattering profile, 1Lipo in the lamellar structure does not adopt a uniform head/tail orientation. Such defective donor and acceptor arrays likely contain a large number of trapping sites, leading to short-lived charge carriers, as observed by a flash photolysis time-resolved microwave conductivity study.