Large intrinsic birefringence in zinc-blende based artificial semiconductors

A new attempt to solve the phase matching problem for semiconductor-based frequency conversion devices, based on the implementation of intrinsic birefringence in artificial materials, is discussed. The first results concerning the growth and characterization of ultrashort period superlattices are presented. To cite this article: J.-M. Jancu et al., C. R. Physique 8 (2007).     

Supersymmetry and its spontaneous breaking in the random field Ising model

We provide a resolution of one of the long-standing puzzles in the theory of disordered systems. By reformulating the functional renormalization group for the critical behavior of the random field Ising model in a superfield formalism, we are able to follow the associated supersymmetry and its spontaneous breaking along the functional renormalization group flow. Breaking is shown to occur below a critical dimension d(DR) ? 5.1 and leads to a breakdown of the "dimensional reduction" property. We compute the critical exponents as a function of dimension and give evidence that scaling is described by three independent exponents.     

Spin-wave eigenmodes of a saturated magnetic square at different precession angles

Using low-loss dielectric magnetic films in combination with space-resolved Brillouin light scattering spectroscopy we have studied nonlinear modification of eigenmode spatial distributions in saturated magnetic squares. We have found that, as the angle of magnetization precession increases, the eigenmode spatial distributions experience significant qualitative changes due to a nonlinear coupling between forming them standing spin waves. We show that the found nonlinear eigenmodes cannot be described by means of the linear theoretical approach even qualitatively.     

Crystalline Pr:SrAl12O19 waveguide laser in the visible spectral region

We fabricated waveguides in Pr:SrAl(12)O(19) crystals by direct femtosecond laser writing. The propagation losses were calculated to be as low as 0.16 dB/cm at a wavelength of 633 nm. Laser oscillation in a diode-pumped waveguide at a wavelength of 643.5 nm was realized. The output power of the waveguide laser was 28.1 mW at a slope efficiency of 8%.     

A neutron powder diffraction study of the helimagnetic structure of TlCo2Se2−xSx

The magnetic layer structure of TlCo₂Se_2−xS_x has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged within the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo₂Se₂ form a helix along the c-axis with a turning-angle of ∼119° at 1.4 K. This kind of helical structure prevails for 0≤x≤1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34°, showing an almost linear relationship with the interlayer distance of Co-Co. For x≥1.75 the interlayer coupling changes to ferromagnetic. Unexpectedly, two helices were found to coexist at x=0.5 and x=1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106°, resp., 73°) together with a commensurate angle of 90°. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites.     

Quark-hadron duality in neutron (3He) spin structure

We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_{1} of the neutron and 3He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c);{2}. Global duality is observed for the spin-structure function g_{1} down to at least Q;{2}=1.8 (GeV/c);{2} in both targets. We have also formed the photon-nucleon asymmetry A1 in the resonance region for 3He and found no strong Q2 dependence above 2.2 (GeV/c);{2}.     

Vibro-acoustic noise control treatments for payload bays of launch vehicles: Discrete to fuzzy solutions

Sound transmitted through an enclosing structure into a cavity has been minimised by optimising the locations, numbers and properties of tuned mass dampers placed on the structure and Helmholtz resonators placed in the cavity. Most of the results presented in the literature show the effect of a few well selected acoustic or vibration absorbers on simple vibro-acoustic systems, whereas the results presented here indicate the trends that occur when a few absorbers are replaced by a large number. The results indicate that for low numbers of absorbers, the result of the optimal configuration is to reduce the response of discrete modes, and for a large number of absorbers the result of the optimal configuration is a tendency for the vibro-acoustic energy to be smeared over a range of frequencies, which is similar to the results seen in fuzzy structures. The enormous computational task was achieved using a distributed computing network and an asynchronous parallel genetic algorithm.     

DMANS——一种新型荧光闪烁体染料的寿命与能量转移的研究

本工作对一种新型荧光闪烁体染料——4-二甲胺基—4''硝基芪(DMANS)在不同介质中的光谱行为和能量转移进行了研究,发现介质的极性大小以及介质和染料间的能量转移对该闪烁体染料的荧光量子产率和闪烁发光延迟具有重大影响。研究对选择基体材料和合理组成闪烁材料配方有一定的参考价值。