A novel approach for compensation of birefringence in cylindrical Nd: YAG rods

A new concept for compensation of birefringence in solid-state rod lasers is presented. The basic idea of our approach is the simultaneous use of an in-cavity polarization rotator and an imaging optical system between the two passes through the laser rod. The theoretical analysis based on matrix optics shows that perfect compensation for the birefringence and bifocusing in laser rods is possible for a large pumping range. Experimental results with two Nd:YAG rods are also presented. The measured depolarization loss per transit for a test beam at 0.63 m is less than 5% for pumping power up to 6kW per rod. This would allow efficient generation of high-power TEM₀₀ mode and linearly polarized multimode output power from Nd:YAG oscillators in rod geometry.     

The study of neutral pion azimuthal distribution in 58Ni+58Ni reaction at 2 GeV/nucleon

In order to study the anisotropic azimuthal emission of mesons in heavy ion collisions we measured the neutral pions emitted in the Ni+Ni collisions at 2 GeV/u with respect to the reaction plane. We studied the strength of the azimuthal anisotropy for neutral pions in dependence of the transverse momentum and impact parameter. The preliminary results and their comparison with previous experimental data are reported.     

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Viscoelastic properties of a silicone resin during crosslinking

Viscoelastic properties of a silicone resin crosslinked at various extents were characterised by means of rheology. The influence of temperature on the viscoelastic properties of the material as-delivered and in a state pre-crosslinked approximately to the gel point has been investigated by dynamic-mechanical measurements. While the glass transition temperature is increased by the crosslinking, no changes of the free volume fraction at T _g and its thermal expansion coefficient were observed. Taking the different glass transition temperatures into account, it could be shown that the corresponding WLF-parameters are the same. The molar mass and, hence, the viscosity of the material can be increased by a heat treatment. The dependence of the zero shear-rate viscosity on the weight average molar mass indicates that the existence of entanglements of the polymer molecules is not very probable.     

Selectivity ratios of cation-sensitive glass electrodes in ethanol-water mixtures

Summary The response of cation-sensitive glass electrodes to univalent cations in ethanol-water mixtures shows increasing e.m.f. values with increasing fractions of ethanol for Na⁺, K⁺, Cs⁺, Rb⁺, Li⁺, and NH₄ ⁺, but anomalous behavior for H⁺. The calculated selectivity of the glass electrode for metal ions over the hydrogen ion thus increases sharply over the range of 10–70 weight % ethanol. It is suggested that sodium rather than hydrogen ion may be adopted as the reference ion for the definition of selectivity ratios in mixed solvents.

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Zusammenfassung Die Ansprechbarkeit von kation-empfindlichen Glaselektroden auf einwertige Kationen (Na⁺, K⁺, Cs⁺, Rb⁺, Li⁺, NH₄ ⁺) in Äthanol-Wassergemischen weist mit steigendem Äthanolgehalt steigende E.M.K.-Werte auf; H⁺ zeigt ein abweichendes Verhalten. Die berechnete SelektivitÄt der Glaselektrode für Metallionen nimmt daher im Bereich von 10–70% Äthanol stark zu. Es wird empfohlen, für die Definition von SelektivitÄtsverhÄltnissen in Lösungsmittelgemischen Na⁺ an Stelle von H⁺ als Bezugsion zu verwenden.

     

Electrical characterisation of SrTiO3/Si interfaces

Deposition of SrTiO₃ (STO) thin films by ultra-high vacuum rf magnetron sputtering was performed in order to produce high-quality STO/p-Si (1 0 0) interfaces and STO insulator layers with high dielectric constants. The deposition temperatures were in the range from room temperature to 550 °C. Capacitance-voltage (C-V) and conductance-frequency measurements showed that the dielectric constant of the films ranges from 55 to 120. C-V measurements on Al/STO/p-Si structures clearly revealed the creation of metal-insulator-semiconductor diodes. The interface state densities (D_it) at the STO/p-Si interfaces were obtained from admittance spectroscopy measurements. The samples deposited at lower temperatures revealed values of D_it between 2×10¹¹ and 3.5×10¹² eV⁻¹ cm⁻² while the higher temperature deposited samples had a higher D_it ranging between 1×10¹¹ and 1×10¹³ eV⁻¹ cm⁻². The above results were also well correlated to X-ray diffraction measurements, Rutherford backscattering spectroscopy, and spectroscopic ellipsometry.     

Observation of Δ+→ pπ0 decay in heavy-ion collisions

Proton-π⁰ coincidences have been measured at the beam energy of 180A MeV in the reaction Ar+Ca studied by TAPS at SIS/GSI. In the proton-π⁰ invariant mass spectrum we observe a significant excess of strength above the background obtained by event mixing. We attribute this signal to the strength distribution N _Δ of the Δ baryonic resonance. No correlation is observed in the case of deuteron-π⁰ coincidences. Assuming isotropic emission of π⁰ and Δ⁺ from a midrapidity thermal source and isospin symmetry, we determined the global N _Δ/N _πratio of 0.79 ±0.30(stat) ±0.2(syst). This value indicates that most pions produced at subthreshold energy in heavy-ion reaction are mediated by the Δ-resonance. Received: 7 April 2000 / Accepted: 29 August 2000     

Investigation of vortex dynamics close to Bc2 in Cu2Mo6S8 quasi epitaxial thin films

The Ginzburg number of superconducting Chevrel phases M_xMo₆S₈ with small coherence length (10⁻³ to 10−5) is intermediate between those obtained for conventional low T_c materials (10⁻⁸) and those of high T_c (10⁻¹) indicating that these phases may display features in the dynamics of the vortices similar to those observed in high T_c superconductors. In this work we present a detailed study of I–V measurements close to the B_c2 line carried out on quasi epitaxial thin films of Cu₂Mo₆S₈. The non-linear I–V curves show a scaling behaviour making possible to determine a transition temperature between an unpinned vortex state and a vortex glass state. However, the temperature range of the unpinned vortex state is much wider than expected.