Optical detection of magnetic stray fields

The magnetic stray field caused by defects in ferromagnetic parts is indicated by means of magneto-optics. Using thin ferromagnetic films as the magneto-optic medium, surface cracks in steel with a width of 0.015 mm and sub-surface defects (bores with a diameter of 1.75 mm) 21 mm below the surface are detected.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.     

Modelling of self-aligned total internal reflection waveguide mirrors: an interlaboratory comparison

Results of modelling of light propagation in 45° self-aligned total internal reflection rib waveguide mirrors on InP substrate are compared. Six laboratories participated in the comparison with the following six modelling methods: the standard fast-Fouriertransform beam propagation method (BPM), the standard finite-difference (FD) BPM using the Crank-Nicholson scheme (two laboratories), the FD-BPM with the correction for the slowly varying envelope approximation, the method of lines, the eigenmode expansion and propagation method, and a simple method based on the field overlap. All the laboratories used the effective-index method to reduce the three-dimensional problem to two dimensions. The differences among the results obtained by different methods are briefly discussed and qualitatively compared to measured values.     

Design of 1480-nm diode-pumped Er3+-doped integrated optical amplifiers

Abstact Erbium-doped Y₂O₃ integrated optical amplifiers are designed for low-threshold operation and 3 dB amplification. The most important design parameter for minimal threshold, the erbium concentration, is found to have an optimum value of 0.35 at% for a given waveguide structure with 1.0 dB cm^-1 background loss. The corresponding threshold power is 7 mW. The pump power to obtain 3 dB gain is found to be 22 mW for an amplifier with an optimum erbium concentration of 0.6 at% and 2.8 cm length. At 30 mW pump power the maximum gain is shown to be 5 dB.Designing is done using a comprehensive numerical model of an erbium-doped integrated optical amplifier. In the model two-dimensional intensity-dependent overlap integrals are used, which allow arbitrary erbium dopant profiles and waveguide crosssections. Concentration-dependent effects such as quenching and upconversion are also included in the model.Input parameters for the model are determined from measurements on an unoptimized Er: Y₂O₃ optical waveguide amplifier. Amplification simulations and gain measurements of the unoptimized waveguides are found to be in close agreement, providing a sound basis for the design calculations.     

Measuring mechanical properties of ferromagnetic materials by internal induction

The voltage which is generated during the reversal of the magnetization inside the ferromagnetic specimen itself is measured. This internally produced voltage is sensitive to external forces and internal stresses. The method is compared with the application of strain gages.     

A remark on the intersection arrays of distance regular graphs and the distance regular graphs of diameter d = 3i − 1 with b i = 1 and k > 2

Let be a distance regular graph with intersection array b ₀, b ₁,..., b _d–1; c ₁,..., c _d. It is shown that in some cases (c _i–1, a _i–1, b _i–1) = (c ₁, a ₁, b ₁)and (c _2i–1, a _2i–1, b _2i–1) imply k 2b _i + 1. As a corollary all distance regular graphs of diameter d = 3i – 1 with b _i = 1 and k > 2 are determined.     

Dispersive power and crossover temperature,TCO, of two polar nematic liquid crystals in the visible spectral region

Refractive index studies are carried out on two highly polar liquid crystals: 1. N-(p-n-methoxy benzylidene)-p-amino benzonitrile, PmBAB, 2. N-(p-n-ethoxy benzylidene)-p-amino benzonitrile, PeBAB. The experimental investigations are carried out in the visible region at four different wavelengths, namely, 633, 589, 546 and 436 nm. The two compounds exhibit only the nematic liquid crystalline phase in between the isotropic and crystalline solid. The dispersive power ω is estimated for two consecutive wavelengths for the case of <n>, n_e and n_o for different wavelengths and found to be constant with temperature. Further the temperature gradients of n_e and n_o are estimated, and the crossover temperature is obtained using dn_o/dT for all the wavelengths.     

Mikroskopische Beobachtung gerader und gekrümmter Magnetisierungsstrukturen mit dem Faraday-Effekt

Ferromagnetic domains in thin evaporated films of iron have been made visible by means of the Faraday effect following Fowler and Fryer and by use of a microscopic high-resolution technique. Domains with straight and curved directions of magnetization have been observed. Curved domains can also be interpreted as Néel-walls with small curvature.