Magnetic properties of amorphous alloys

The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline multilayers has been discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Laser systems specialized for laser spectroscopy at storage rings

Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser systems specialized on the specific needs of laser spectroscopy at storage rings is reported. Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator. It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz. This laser can be advantageous for laser cooling of ion beams. This revised version was published online in August 2006 with corrections to the Cover Date.     

Role of stationary photon statistics in a high-Q cavity mode while it is exciting the active laser medium

It has been shown by Yu. M. Golubev, M. I. Kolobov, and I. V. Sokolov, Zh. éksp. Teor. Fiz. 111, 1579 (1997) [JETP 84, 864 (1997)], that when an optical cavity is excited by external radiation from a sub-Poisson laser the cavity mode may be in either a sub-Poisson or a Poisson stationary state. This is not important for a resonant medium which is excited into the upper laser level while interacting with this mode inside the cavity. The degree of regularity of the excitation will be identical to that of the initial light flux incident on the cavity, and this ultimately ensures the same sub-Poisson lasing as for strictly regular pumping of the resonant medium. Zh. éksp. Teor. Fiz. 113, 1223–1234 (April 1998)     

Experimental Determination of Four-Time Stimulated Echoes in Liquids, Colloidal Suspensions, and Crystals

Four-time stimulated echo experiments have been used to monitor the temporal evolution of the reorientation rates of deuterated molecules or colloidal suspensions. We present extended phase cycles for this seven-pulse experiment. In order to test its performance three vastly different materials are chosen. These include a crystal in which the molecules carry out well-defined 180° flips and a supercooled liquid characterized by a distribution of jump angles centered around 10°. As an example for rotational diffusion, data on a concentrated suspension of polystyrene spheres in a viscous medium are presented.     

Superradiance of polaritons in finite one-dimensional crystals of increasing length: Passage from a dimer to an infinite crystal

Solutions of the dispersion equations for polariton states in finite one-dimensional crystals of arbitrary length are obtained. The appearance and evolution of the radiative and nonradiative polariton branches are traced as the length varies from two monomers to limiting values, above which the spectrum no longer undergoes significant changes. The dependences of the frequencies and radiative widths on the polariton wave vector are found for various orientations of the dipole moment of the quantum transition. The evolution of superradiance as the length of the crystal increases is traced. Some previously unknown significant features of the polariton spectrum are noted particularly the damping of the branch traditionally termed nonradiative as a consequence of emission from the end faces. Fiz. Tverd. Tela (St. Petersburg) 40, 2136–2140 (November 1998)     

Observation of ionic thermocurrents in zirconia-based solid electrolytes

In ionic conductors, long range-migrating charges are a main cause of polarization processes. This has complicated, up to date, the study of ionic thermocurrents (ITC) in solid electrolytes. However, the method is appealing, as it probes directly charge-formation phenomena that are important both from a scientific point of view and for applications. This work reports on the observation of ITC in solid electrolytes. Under appropriate experimental conditions, the ITC response of a zirconia sample electroded with platinum is a reproducible one, thus opening the way to a new characterization method that may complement other well established methods, such as Impedance Spectroscopy and a number of electrochemical techniques. The general trends of the response, which is composed of two well resolved ITC peaks, is discussed. One of them, taking place at higher temperatures, conforms to the standard shape of a first order kinetics depolarization process. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Monte Carlo determinations of the beta dose rate to tooth enamel

The results of Monte Carlo simulations of the beta dose rate to enamel are presented. The dose rates are the most comprehensive to date, incorporating the beta spectrum from 21 different radionuclides, all internal conversion and Auger electrons, the majority of the bremsstrahlung radiation, effects due to radon loss in the uranium series, and variations in the moisture content of the sediment. Applications to a new dating technique in archaeology using electron spin resonance and beta-gradient isochrons are discussed.     

MO analysis of macroscopic supercurrent flow in MgB 2

We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB₂. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis. A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration, at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a network of strongly coupled Josephson junctions. Received 31 May 2001 and Received in final form 5 December 2001     

Diffractive heavy vector meson production from the BFKL equation

Diffractive heavy vector meson photoproduction accompanied by proton dissociation is studied for arbitrary momentum transfer. The process is described by the non-forward BFKL equation, for which a complete analytical solution is found, giving the scattering amplitude. The impact of non-leading corrections to the BFKL equation is also analysed. Results are compared to the HERA data on production. Received: 2 July 2002 / Revised version: 29 August 2002 / Published online: 18 October 2002