DFB lasers with integrated electroabsorption modulator

We present high-performance 1550 nm DFB lasers with butt-coupled, bulk type integrated electroabsorption modulators of good manufacturability and reliability. Key issues in device design are reviewed and the strong influence of the exact detuning between lasing wavelength and modulator bandgap is demonstrated. Fibre-coupled output powers as large as 6 dBm and attenuation efficiencies as high as 12 dB V^–1 are obtained. Butterfly-packaged devices show only 1 dB penalty for 10 Gbit s^–1 NRZ transmission over 50-km standard single-mode fibre (SMF) without the use of an optical amplifier. With an optical booster amplifier, self-phase-modulation in the fibre is exploited and repeaterless 10 Gbit s^–1 transmission is possible over 150-km standard SMF.     

Oxygen transfer during the copper induced reaction of α,β-epoxy diazomethyl ketones

Reactions of α,β-epoxy diazomethyl ketones 1a-1with activated copper powder or copper(II) sulfate in methanol (or ethanol) lead to 1,1 - dialkoxy - but - 3 - ene - 2 - ones 2 (or 3) in good yields. This process of oxygen transfer proceeds via initially generated keto-carbenoids which react intramolecularly with the epoxide function to give bicyclic intermediates 10. Release of strain and subsequent ring opening produces but - 3 - ene - 1,2 - diones which acetalise to give the ultimate reaction products 2 (or 3). With copper as catalyst byproducts were isolated, viz 1,1 - dialkoxy - 4 - hydroxy - butane - 2 - ones (4 and 5), and indanone derivative 6. An explanation for these side reactions has been given.     

Study of the residual linewidth of the level-anti-crossing signal in p-benzoquinone

The linewidth of the level-anti-crossing (LAC) signal in p-benzoquinone has been examined using optical detection of magnetic resonance between states in the avoided crossing region. The results are used to separate the homogeneous (due to hyperfine coupling) from the inhomogeneous (due to disorder) contribution to the LAC linewidth.     

Copper(I) thiolate catalysts in asymmetric conjugate addition reactions

[structure: see text] Full conversion and enantioselectivities up to 83% have been obtained in the conjugate addition reactions of diethyl zinc to Michael acceptors catalyzed by well-defined (chiral) copper(I) aminoarenethiolates. Interesting differences between organozinc or Grignard reagents have been found: for cyclic enones R(2)Zn reagents afford better results, whereas earlier work showed that RMgX reagents react more selectively with acyclic enones.     

Distribution and thickness of the surface contaminations on STM tungsten tips,studied by AES/SEM and ARXPS

The combination of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and angle resolved X-ray photoelectron spectroscopy (ARXPS) has been applied to the analysis of the distribution of elements at the surface region of electrochemically etched tungsten tips and the determination of the thickness of a layer with oxygen and carbon contamination. Auger line profiling revealed a homogeneous distribution of oxygen and significant enrichment of carbon on the W tip between 0 and 1.5 m from the top. The thickness of the contamination layer on various W materials, electrochemically etched, was found to be 1.35±0.15 nm as measured using ARXPS, and was estimated to be about 1–3 nm as measured by AES.     

Excited-state dynamics of the intramolecular proton transfer of 3-hydroxyflavone in the absence of external hydrogen-bonding interactions

A single exponential risetime is observed for the lautomer fluorescence of 3-hydroxyflavone in the absence of hydrogen-bonding impurities in the temperature range of 298—77 K. The observed risetime in hydrocarbon solvents is less than 8 ps at 298 K, while at 77 K it is 37 ± 6 ps. The discrepancy with other reports is attributed to hydrogen-bonding solvent impurities which inhibit the intramolecular proton transfer process.     

Storage possibilities for radioactive krypton (85Kr)

A review of the different storage possibilities for radioactive krypton (⁸⁵Kr) is given. Various strategies can be applied to store⁸⁵Kr safely over many decades: storage in pressure containers and encapsulation in various solid matrices.     

Synthesis, microwave-assisted polymerization, and polymer properties of fluorinated 2-phenyl-2-oxazolines: a systematic study

We present a detailed systematic study of the synthesis and ability of fluorinated 2-phenyl-2-oxazolines to undergo polymerization. The synthesis of these compounds is based on a two-step procedure that gives the desired 2-oxazolines in moderate-to-good yields. All the compounds were fully characterized by IR and NMR ((1)H, (13)C, and (19)F) spectroscopy, mass spectrometry, and elemental analysis. The 2-oxazolines were subsequently used as monomers for living cationic ring-opening polymerization (CROP) with microwave irradiation as the heat source (T=140 degrees C), nitromethane as the solvent, and methyl tosylate as the initiator. The linear first-order kinetic plots of the polymerizations accompanied by a linear increase of the molecular weight with conversion and low polydispersity index (PDI) values (generally below 1.30) indicate a living polymerization mechanism. The resulting polymerization rates reflect a strong sensitivity to the quantity of fluorine substituents in general and the presence or absence of ortho-fluoro substituents of the phenyl ring in particular. All the polymers were isolated and characterized by size-exclusion chromatography and MALDI-TOF mass spectrometry. Finally, a detailed investigation of selected polymer properties was performed by using differential scanning calorimetry, thermogravimetric analysis, and contact-angle measurements, thus resulting in structure-property relationships. Whereas the thermal properties of the polymers are mostly influenced by the presence of ortho-fluoro substituents, the surface properties are mainly determined by the presence of para- and/or meta-fluoro substituents.     

Probing the electronic structure and conformational flexibility of individual light-harvesting 3 complexes by optical single-molecule spectroscopy

We present fluorescence-excitation spectra of individual light-harvesting 3 (LH3 or B800-820) complexes of Rhodopseudomonas acidophila at 1.2 K. The optical single-molecule studies were employed to investigate the electronic structure as well as the conformational flexibility of the individual pigment-protein complexes. The optical spectra resemble those of individual light-harvesting 2 (LH2) complexes, in agreement with the structural similarity of both types of complexes. Although variations among the LH3 spectra are large, there is a distinct difference in the spectral features of the 800 and 820 nm region that appears in all the complexes studied. In the B800 region 4-6 narrow bands are present whereas in the B820 region a limited number of relatively broad bands are observed. These observations can generally be interpreted in terms of localized excitations in the 800 nm region and delocalized excitations in the 820 nm region. The observed heterogeneous spectral behavior, especially in the B820 band, indicates that the B820 pigments of LH3 are sensitive to light-induced local conformational changes. It is suggested that a rotation of the C(3)-acetyl chain of a BChl a pigment bound to the beta-subunit of the light-harvesting complex is the origin of the conformational flexibility and affects the optical properties of the whole pigment-protein complex.