The CO fundamental-band laser as secondary frequency standard at 5 µm

We present a very high-resolution heterodyne spectrometer based on a CO laser which operates down to fundamental-band transitions of the molecule. This allows us to detect saturated absorption signals on these transitions at very low pressure (0.4 Pa) and laser intensity (< 1 mW/cm²), yielding a linewidth of about 250 kHz. With the CO fundamental-band laser stabilized to these saturation signals we have measured the transition frequencies of the fundamental bands of three isotopic species to an accuracy of typically 20 kHz (v/v 3 × 10^–10), referenced to the CO₂ frequency standard. Together with additional frequency measurements of the first hot bands, these provide the first heterodyne frequency data of sub-Doppler accuracy for transitions in low lying bands of CO. They now represent the most accurate secondary frequency standard in the spectral region around 5 µm (60 THz).     

Spectro-streak picosecond studies of intramolecular charge-transfer fluorescence

A spectro-streak photometer, an instrument for simultaneously measuring fluorescence intensity, time, and wavelength,I(t, ), with a single picosecond excitation pulse, has been constructed. Two typical and currently highly topical examples of mesurements are discussed. (1) the temporal development of the fluorescence form the intramolecular charge-transfer (ICT) state of the rigid aromatic compound 4,5-(1-methylindolino)3,4-naphthanthracene is studied in the protic solvent hexanol. (2) Propyl chain-linked pyrene/N,N-dimethylaniline is used as the model compound to study conformational changes associated with the transition from a contact ion pair to a sandwich exciplex.     

Photorefractive properties of ruthenium-doped potassium niobate

Photoconductivities and photovoltaic currents of ruthenium-doped KNbO₃ are orders of magnitude larger than that of undoped and ion-doped crystals. KNbO₃:Ru is very sensitive for holographic recording with red light and the photovoltaic current increases sublinearly with light intensity.     

Prospects and limitations of an isotope tracer technique for understanding sulfur cycling in forested and agro-ecosystems

Abstract Applications of isotopically distinct sulfur compounds have recently been used for tracing the fate of added sulfur in whole catchments or sub-compartments therein. Basic principles, the analytical methodology, and data evaluation for this isotope tracer technique are briefly described. We recommend that δ(34)S-values of applied and natural sulfur compounds in the investigated ecosystem should differ by more than 20‰ in order to successfully ascertain sulfur fluxes. Where possible, a high ratio of applied sulfur loads versus sulfur pool sizes in the ecosystem should also be realized in order to allow the assessment of sulfur transformations in the study area. Prospects and limitations of this isotope tracer technique are critically discussed by reviewing results from recently or currently conducted lysimeter and field experiments.     

Laser nitriding of iron: Influence of the laser parameters on the nitriding efficiency

Laser nitriding of Armco iron in nitrogen was studied for KrF-excimer-laser irradiation. The influence of the energy density and number of pulses on the nitrogen take-up and the nitride phases formed was investigated using Resonant Nuclear Reaction Analysis (RNRA) and Mössbauer spectroscopy. Besides the original a-iron, austenite-Fe(N), martensite-Fe(N),-Fe₂₊N, and-Fe₁₆N₂ were identified. The fraction of the e-phase was found to increase with the number of pulses and the energy density. A threshold energy density of 1.8(2) J/cm² for the laser nitriding process was found.     

Topologically nontrivial field configurations in noncommutative geometry

In the framework of noncommutative geometry we describe spinor fields with nonvanishing winding number on a truncated (fuzzy) sphere. The corresponding field theory actions conserve all basic symmetries of the standard commutative version (space isometries and global chiral symmetry), but due to the noncommutativity of the space the fields are regularized and they contain only a finite number of modes.Part of the Project P8916-PHY of the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich.     

Crossover from Mott to Efros-Shklovskii variable range-hopping in Si:P

The low-temperature conductivity of uncompensated insulating Si:P with P concentration just below the metal-insulator (MI) transition shows with decreasingN a crossover from Mott variable range hopping (VRH) to Efros-Shklovskii VRH. From the concentration dependence of the Mott temperatureT _M a correlation-length exponent ν=1.1 is obtained which is compatible with the conductivity exponent μ=1.3 for metallic samples.     

Observation of Δn=1 dielectronic recombination resonances of boronlike argon

We report here an observation ofn=1 dielectronic recombination resonances of boron-like argon in the energy region 140–195 eV. With the cooler's electron beam as a target, a resolution of approximately 0.6 eV FWHM was obtained in the observed energy range. The energies of the doubly excited states were estimated with a Hartree-Fock calculation, which indicates that the observed resonances are from Ar¹³⁺(1s²2s²2p) to Ar¹²⁺(1s²2s²3l3l) and Ar¹²⁺(1s²2s2p3l3l) transitions.