Efficient sum-frequency generation of continuous-wave single-frequency coherent light at 252 nm with dual wavelength enhancement

Highly efficient frequency conversions were conducted to obtain deep-ultraviolet single-mode coherent light by use of two-stage external cavities. A power of 154 mW at approximately 252 nm was obtained with a conversion efficiency of more than 8% by doubly resonant sum-frequency mixing of 373-nm light from the first-stage conversion and 780-nm light from a single-mode Ti:sapphire laser. The output performance of the deep-ultraviolet light source is sufficient for use in the laser cooling of neutral silicon atoms.     

Fabrication of Nd:KGW film on a Si substrate with a CeO<Subscript>2</Subscript> buffer layer

Highly textured single-oriented (110)Nd-doped potassium gadolinium tungstate [Nd:KGd(WO₄)₂ or Nd:KGW] thin films were successfully fabricated on (100)Si substrate by introducing a (100)CeO₂ buffer layer using KrF-excimer-laser pulsed laser deposition (PLD) at precisely controlled experimental conditions. The CeO₂ buffer layer was also prepared by PLD. Home-made potassium-enriched ceramic targets were prepared and used in order to prevent K deficiency in the film during the deposition. Depositions were performed in both Ar and O₂ environments. The optimal growing conditions achieved from the viewpoint of best crystallinity, optical properties and surface morphology were: d_T–S=4 cm, P(O₂)=0.08 mbar and T_sub=700 °C, respectively. Improvement of the properties of the as-grown films was examined by post-deposition annealing between 700 °C and 900 °C in air. Optical waveguide loss and the photoluminescence spectrum in the 800–1400-nm range were measured. PACS 81.15.Fg; 42.79.Gn; 42.79.Hj     

Development of a high-power deep-ultraviolet continuous-wave coherent light source for laser cooling of silicon atoms

We developed a deep-UV single-mode coherent light source through two-stage highly efficient frequency conversions by use of external cavities. In the first stage, second-harmonic power of 500 mW was obtained by frequency doubling of a 746-nm Ti:sapphire laser with a conversion efficiency of 40%. In the second stage, 50-mW power at ~252nm was obtained by doubly resonant sum-frequency mixing of 373-nm light from the first-stage conversion and 780-nm light from a diode laser. The output performance of this deep-UV light source is sufficient for laser cooling of neutral silicon atoms.     

Post-deposition atomic terraces growth of ZnO thin films deposited on epi-GaN templates

We demonstrate how growth processes affect on ZnO film properties, which are to be essential guides to prevent defect formation in order to synthesize reproducible high quality ZnO films. First, we reveal that deposition at a low temperature is indispensable to transfer underlying GaN atomic terraces to ZnO surface. As the film thickness is increased, however, the terraces disappear to develop island morphology. It is found that the thick film surface is smoothed to the extent that atomic terraces can be seen after an appropriate thermal treatment. Adverse effects associated with high annealing temperatures are then demonstrated as evidenced by cracks formation, increased yellow cathode-luminescence and intermixing at the interface.     

Synthesis and crystal structure of sodium borosilicide, Na8B74.5Si17.5

Ternary sodium borosilicide, Na(8)B(74.5)Si(17.5), was newly synthesized by heating a mixture of sodium, silicon and amorphous or crystalline boron at 1073-1273 K. The crystal structure of the black hexagonal prismatic single crystal obtained at 1273 K was analyzed. The X-ray diffraction reflections of the crystal were indexed with hexagonal cell parameters a = 10.2392(3) ? and c = 10.9215(4) ? (space group P6(3)/mmc, No. 194). The structural formula could be represented as Na(8)(B(12))(6)Si(16)[BSi](1.5)[B(2)](0.5). B(12) icosahedra form a three-dimensional framework having small triangular and large hexagonal channels along the c axis. Chains of [-Si-(Si-Si)(3)-Si-] surrounded by Na atoms are located in the large channels. Trigonal prism cages for Na atoms and for atom pairs of Si-B or B-B are alternately arrayed in the small channels. The ratio of Si-B and B-B pairs in the cage is around 3:1.     

Synthesis and characterization of manganese and cobalt pyroborates: M2B2O5 (M = Mn,Co)

The magnetic property of Co₂B₂O₅ and the optical property of M₂B₂O₅ (M = Mn, Co) were investigated. Co₂B₂O₅ showed antiferromagnetic behavior below the Néel temperature of T_N ≈ 45 K, and the Weiss temperature was T_W = +7.7 K. The effective magnetic moment of Co was 4.96 μ_B, which indicated that Co was divalent and in a high-spin state. Absorptions attributed to the d–d transitions in Mn²⁺ and Co²⁺ ions were observed at 250–650 nm in the diffuse reflection spectra. The optical absorption edges of Mn₂B₂O₅ and Co₂B₂O₅ were at 243 nm (5.11 eV) and 299 nm (4.15 eV), respectively.     

Distribution, absorption and excretion of 198Au-colloid and Na251CrO4 in the chicken (author's transl)]

In order to clarify the suitability of 198Au-colloid and Na251CrO4 as a marker of transit of the gastrointestinal content of the chicken, the distribution, absorption and excretion of 198Au-colloid and Na251CrO4 in the chicken were examined. Orally administered 198Au-colloid was not absorbed by the gastrointestinal tract and excreted into feces. Intravenously injected 198Au-colloid was not excreted into the gastrointestinal tract through the gastrointestinal wall. On the other hand, orally administered Na251CrO4 was relatively well absorbed by the gastrointestinal tract and distributed over a whole body. Intravenously injected Na251CrO4 was excreted into the gastrointestinal tract through the gastrointestinal wall and bile ducts. It seemed that 198Au-colloid was not adhered to the gastrointestinal mucosa and consequently, the transport of 198Au-colloid in the gastrointestinal tract was not delayed. It is concluded that 198Au-colloid is highly suitable as a marker of gastrointestinal transit of the chicken but Na251CrO4 is unsuitable.