Phase modulation of the signal beam in three-wave forward mixing in photorefractive bismuth silicon oxide

The interaction of three forward beams in a BSO crystal is investigated under conditions when the two pump beams are anti-symmetrically detuned and the signal beam is phase modulated. For sinusoidal phase modulation the signal gain is shown to be dependent on the instantaneous frequency detuning. Single and double maxima in gain are obtained depending on the voltage amplitude applied to the piezoelectric mirror. For triangular phase modulation a slight asymmetry is found in the gain versus detuning curve.     

Domain wall pinning by defects and the C-I transition

The influence of randomly distributed defects on domain wall fluctuations is investigated. These fluctuations lead to the long-range repulsion between domain walls resulting in the experimentally observed n;～ √z.sfnc;T;? T_cz.sfnc; behaviour of the domain wall density near the C-I transition. The impossibility of thermal depinning of one domain wall in the impurity potential is also shown.     

Rearrangements in an alkylthiolate self-assembled monolayer using electrostatic interactions between nanoscale asperity and organomercaptan molecules

Chemically induced rearrangements of amphifunctional molecules have been demonstrated using strong nonuniform electric fields (10(8)-10(10) V m(-1)) induced in the vicinity of nanoscale asperities. Electrostatic interactions utilizing these rearrangements of alkylthiolates assembled on Au(111) result in the nanopatterning of raised nanostructure (1.5-9 nm high, 15-100 nm wide) arrays on a second time scale by manipulating an atomic force microscope (AFM) tip above the monolayer. It is suspected that, as a result of the oxidative cleavage initiated by a weak bias of the tip, the S end of the alkylthiolate chain carrying a sulfenium cation is attracted to the (lifting) tip, forming bi- and higher-layer structures in the vicinity of the tip apex. Stabilization of the multiple-layered structures is accomplished via mutual attraction and entanglement of hydrocarbon chains. The rearrangements suggest a novel and general approach for nanoscale architecture in self-assembled systems.     

Amphiphilic macrocyclic nickel(II) complex in a liquid-crystalline matrix: Specific effects of conductivity and self-organization

A study was made of the influence of an amphiphilic macrocyclic nickel(II) complex on the electrical and electro-optic properties of liquid-crystalline systems based on ZhK-440I. It was shown that addition of this complex leads to a decrease in the electrohydrodynamic instability threshold and formation of unusual tetragonal ordered structures in the systems studied.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 6, pp. 522–526, November–December, 1993.The authors wish to express their gratitude to the Fundamental Research Fund of the General Committee of Science and Technology of the Ukraine for financial support of this investigation (Projects 3/114 and 46/3-2).     

First order phase transition in the system of two coupled fields with different transition temperatures

It is shown that for the case of a strong field coupling in the system of two fields the low temperature phase may be stable in the fluctuation region of the high temperature phase.     

Ferromagnet–superconductor hybrids

The new class of phenomena described in this review is based on the interaction between spatially separated, but closely located ferromagnets and superconductors, the so-called ferromagnet–superconductor hybrids (FSH). Typical FSH are: coupled uniform and textured ferromagnetic and superconducting films, magnetic dots over a superconducting film, magnetic nanowires in a superconducting matrix, etc. The interaction is provided by the magnetic field generated by magnetic textures and supercurrents. The magnetic flux from magnetic structures or topological defects can pin vortices or create them, changing the transport properties and transition temperature of the superconductor. On the other hand, the magnetic field from supercurrents (vortices) strongly interacts with the magnetic subsystem, leading to formation of coupled magnetic–superconducting topological defects.

The proximity of ferromagnetic layer dramatically changes the properties of the superconducting film. The exchange field in ferromagnets not only suppresses the Cooper-pair wavefunction, but also leads to its oscillations, which in turn leads to oscillations of observable values: the transition temperature and Josephson current. In particular, in the ground state of the Josephson junction the relative phase of two superconductors separated by a layer of ferromagnetic metal is equal to?π?instead of the usual zero (the so-called π-junction). Such a junction carries a spontaneous supercurrent and possesses other unusual properties. Theory predicts that rotation of magnetization transforms s-pairing into p-pairing. The latter is not suppressed by the exchange field and serves as a carrier of long-range interaction between superconductors.     

Nanolithography Considerations for Multi-Passband Grating Filters

The placement accuracy and resolution of direct-write patterning tools, in particular the atomic force microscope (AFM), is considered for application to fabricating multi-passband integrated optical niters. Because of its simpler fabrication a grating structure is proposed that consists of identical stripes that are non-periodically spaced. The recently developed pseudorandom encoding method from the field of computer generated holography is modified to effectively assign analog reflectances at each point along the grating by selective withdrawal and offsetting of the stripes from a periodic spacing. An example filter designed by this method has two 1.5 nm bandwidth passbands and –23 dB of rejection for lightly coupled stripes. As with single band filters, the passbands broaden as the coupling increases. A calculation of the coupling coefficient of stripes on a fundamental mode, slab waveguide indicate that stripes on the order of 100 nm in depth and width support low insertion loss, multipassband filtering applications at visible wavelengths. Lines of these dimensions patterned with an AFM on (110) silicon indicates the feasibility of fabricating these filters. These conclusions are specific to current AFM’s that are limited to writing fields of 100 μm. Increased rejection and decreased passband widths will result from incorporating precise field stitching into future AFM’s.