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  • 1
    ISSN: 1432-0649
    Keywords: PACS: 42.55.Ye
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. cw Raman lasing of Na2 molecules generated in a heated, sealed-off, all-sapphire cell is demonstrated. Being not damaged by highly corrosive alkaline vapours, this type of cell enables operation without buffer gas in contrast to the normal heatpipe operation of these lasers. This allows us to study Raman lasers in alkaline vapours in new regimes and under ideal conditions. With an argon ion pump laser at 488 nm, Raman laser operation at 525 nm with more than 10% efficiency and thresholds below 0.2 mW for a cell without buffer gas (length 9 cm) have been obtained so far. The low thresholds, being a factor of 10 less than for comparable heatpipe operation, gives us the chance to use low-power diode lasers as pump sources and to realize compact reliable Raman laser systems.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0649
    Keywords: PACS: 13; 42.50; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract.  In a double-Λ level configuration of Na2 molecules, involving rotational–vibrational levels of the X, A and B bands, continuous resonant frequency mixing ω4=ω1−ω2+ω3 is demonstrated. A DCM dye laser at 661 nm (λ1) pumps a molecular Raman laser at 746 nm (λ2) in a sodium heatpipe, which is used to generate the molecular vapour. In the same heatpipe, both fields are mixed with the radiation of an argon-ion laser at 514 nm (λ3) to generate up-converted laser radiation at 473 nm (λ4). For laser powers of 200 mW (λ1), 700 mW (λ2, internal power) and 140 mW (λ3), an output power of 120 μW (λ4) has been achieved. Dependences of the generated radiation on the pump fields (powers and detunings) and polarization features are presented; influences of coherent coupling and population transfer mechanisms are discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 46. Tetrarubidiumhexaphosphide and Tetracesiumhexaphosphide. Preparation, Structure, and Properties of Rb4P6 and Cs4P6Tetrarubidium and tetracesiumhexaphosphide have been prepared quantitatively by reaction of the elements in sealed Nb ampoules at 870 K and 920 K, respectively. Both compounds are black semiconductors (EG ≍ 1.3 - 1.6 eV) and show metallic lustre. Their crystal structures are orthorhombic defect variants M4P6□2 of the hexagonal AlB2 type structure. Characteristic building units are planar isometric P6 rings with bond lengths d(P—P) = 215 and 214 pm, respectively, representing an aromatic 10° system with one double bond, delocalized about six bonds. Thermal decomposition in Ta crucibles yields quantitatively M3P7. The compounds M4P6 disproportionate in ethylendiamine into M3P7, and M3P, as revealed by 31P n.m.r. spectra. In the down field region a singulett (Δ(α-K4P6) = 331; Δ(Rb4P6) = 337; Δ(Cs4P6) = 348) is observed, which can be ascribed to the valence tautomeric hexaphosphene (4). The internal vibrations of the P6 ring have been observed by i.r. and raman-spectra. For Cs4P6 the fundamental vibrations are v(A1g)=356 cm-1 and v(E2g)=507 and 202 cm-1, respectively, and show the same sequence as for benzen. Semiempirical LCAO-MO calculations show, that in the series P6n- with n=2,4, 6 the anion P62- is the most stable one but the unit M2P6-1 becomes more stable as the other isomers by forming the M2[μ-(η6-P6)] complex. Among the isomers of P64- the hexagonal planar 10π system is about 7 eV more stable than the isomeric bicyclo-tetraanion.
    Notes: Tetrarubidium-und Tetracäsiumhexaphosphid werden beim quantitativen Umsatz der Elemente bei 870 K bzw. 920 K in Nb-Ampullen erhalten. Beide Verbindungen sind schwarze Halbleiter (EG ≈ 1,3 - 1,6 eV), die Kristalle zeigen metallischen Glanz. Die Strukturen sind orthorhombische Defektvarianten M4P6□2 der hexagonalen AlB2-Struktur mit planaren isometrischen P6-Ringen als charakteristische Baueinheiten. Die Bindungslänge d(P—P) = 215 bzw. 214 pm entspricht einem aromatischen 10° System mit einer über die sechs Bindungen delokalisierten Doppelbindung. Beim thermischen Abbau entsteht quantitativ M3P7. In Lösungen von Ethylendiamin disproportionieren die Verbindungen M4P6 in M3P7 und M3P. Intermediär treten im Tieffeldbereich von 31P-NMR-Spektren jeweils Singulett-Signale auf (Δ(α-K4P6) = 331; Δ(Rb4P6) = 337; Δ(Cs4P6) = 348), die dem valenztautomeren Hexaphosphen(4) zugeschrieben werden. Die inneren Schwingungen der P6-Ringe wurden aus IR-und Raman-Spektren ermittelt. Für Cs4P6 liegen die Fundamentalschwingungen bei n̈(A1g) = 356 cm-1, n̈(E2g) = 507 bzw. 202 cm-1. Diese Abfolge entspricht derjenigen von Benzol. Mit semiempirischen LCAO-MO Rechnungen wird gezeigt, daß in der Reihe P6n- mit n = 2, 4, 6 zwar das Anion P62- das stabilste ist, daß jedoch mit der Bildung eines M2[m̈-(η6-P6)]-Komplexes die Einheit M2P62- wesentlich stärker stabilisiert wird als die übrigen Isomeren. Unter den Isomeren P64- ist das hexagonal-planare 10°System um 7 eV stabiler als der isomere Bicyclus.
    Additional Material: 9 Ill.
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