Mutual Phase Research Articles

Mutual diffusion and phase equilibrium in copolymers of nonyl acrylate and acrylic acid–diglycidyl ether of bisphenol A systems

Mutual diffusion and phase equilibrium in copolymers of nonyl acrylate and acrylic acid–diglycidyl ether of bisphenol A systems

Tunable detection of radiation from HTSC Josephson junction arrays

We have investigated the mutual phase interaction between a single detector junction and a phase-locked three-junction array of high- T c Josephson junctions. The YBCO Josephson junctions were fabricated on a MgO bicrystal substrate. We measured the radiation power of a Josephson-junction array using an off-chip coupled to a radiometer and on-chip coupled to a single junction from centimeter- to millimeter-wave ranges. The Josephson oscillation power excited the resonant mode coupled to the coplanar microstrip loops. Clear self-induced Shapiro steps were observed in the current–voltage curves of the detector junction. The power transfer to the single detector junction was estimated from the modulation of the Shapiro step height. The maximum detected power level was about 7 nW at frequency 150–250 GHz.

On and off-chip detection of radiation from HTS Josephson junction arrays

We have investigated the mutual phase interaction between a single detector junction and a phase-locked three-junction array of high-T/sub c/ Josephson junctions. The YBCO Josephson junctions were fabricated on a MgO bicrystal substrate. In the array junction structure, the dc bias current was fed to the junction array having parallel geometry with each pair of junctions shunted by a superconducting coplanar microstrip superconducting loop. The configuration of bias leads was a series connection of interlocking dc SQUIDs geometry which enables all junctions to oscillate at the same frequency. We measured the radiation power of a Josephson-junction array using an off-chip coupled to a radiometer and on-chip coupled to a single junction from centimeter- to millimeter-wave ranges. Clear self-induced Shapiro steps were observed in the current-voltage curves of the detector junction. The power transfered to the single detector junction was estimated from the modulation of Shapiro step height. The maximum detected power level was about 7 nW at frequency 150-250 GHz. The Josephson oscillation power excited the resonant mode coupled to the coplanar microstrip loops.

Intrinsic BSCCO Josephson junctions on off-axis substrates

Anisotropic transport and microwave properties of intrinsic Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (2212) Josephson junctions fabricated on off-axis substrates were studied. The twin-free thin film 2212 Josephson junctions have been prepared by molecular beam epitaxy (MBE) on LaAlO/sub 3/ [001] substrates tilted 6/spl deg/ toward the [110] direction, and were patterned into a line shape along [110] LaAlO/sub 3/ with 20 /spl mu/m in width. We found that the anisotropy parameter /spl gamma/ was increased from 76 to 120 by the annealing at temperature of 320-350/spl deg/C in the MBE chamber. The coherent Josephson radiation from stacked 2212 intrinsic junctions and their modulation under applied magnetic field were observed at frequency f/sub REC/=1.7 GHz by using a nonresonant detection method. These results confirmed the occurrence of the mutual phase locking of the stacked series array of intrinsic junctions along the c-axis.

Off-Bragg-angle light diffraction and structure of dynamic interband photorefractive gratings

Steady-state and time-resolved off-Bragg-angle diffraction experiments are used to determine the structure and the dynamics of photorefractive gratings induced by interband photoexcitation. In potassium niobate, we identify in such gratings basically a two-layer structure. Close to the surface, we find a space-charge electric field generated by a charge modulation stored directly in the bands. This grating component is typically 50 μm thick, the amplitude of the refractive index modulation is larger than 10-4, and the response time is a few μs for resonant intensities of 100 mW cm-2. This component is also robust under non-resonant illumination. Deeper in the crystal, a second holographic layer extends over a few hundreds of μm, its amplitude is smaller, and its slower response time is in the ms range. The mutual phase shift between the grating components is also determined.

Phase and Period Responses of the Two-Peak Circadian Rhythm of Trigonoscelis gigas Reitter (Coleoptera: Tenebrionidae) for 6-hr Light Pulses

Circadian rhythm of locomotor activity of the desert beetle T.gigas usually has two narrow peaks: morning (M) and evening (E). While entrained with diurnal (Tz = 24 hr) full or skeleton photoperiods, the M peak is precedes light, while the E peak coincides with light. In a variety of natural and laboratory conditions both peaks tend to maintain a stable mutual phase relationship, about 12 hr apart. The phase responses of the M and E peaks were studied using 6-hr, 30 lx green LED-light pulses applied around ct3, ?t12 and ct18. The PRC for the E peak, plotted versus ct0 (extrapolated moment of light-on) as abscissa, had the same position, as the PRC for the M peak. Both PRCs were asymmetric, but in an opposite way: for the M peak the area of phase advances was bigger, than the area of phase delays, while for the E peak, vice versa. The transient PRCs on day 1, 2 etc. did not differ from the steady state PRC, i.e, the phase response was accomplished virtually in one cycle. Period changes were almost all positive (period became longer after a light pulse). The only "dead zone" in the period response curve (decrease of Dt down to zero) was around subjective evening – early night. Here again, the M peak appeared more "eager" to phase advances than the E peak. Our data support the hypothesis that M and E peaks are controlled by putative separate oscillators. These oscillators seem to have different properties, tend to phase shift to a different extent, and are extremely strongly mutually coupled with phases locked at approximately 180°. The asymmetry of properties of the M and E oscillators has a clear adaptive significance.

Generation of a standing wave field using crossing sound beams for acoustic micromanipulation

A novel sound-field generation method for noncontact manipulation of particles has been studied experimentally. Although it was possible to trap particles in water at nodes of a standing wave field generated between a transducer and a reflector and to transport them using a frequency-shifting operation, there were several problems, such as unstable force due to resonance of the sound field and different movement of trapped particles. The present paper describes a method to generate a standing wave field using plural sound sources without a reflector. When two transducers were settled with their sound-beam axes crossing to each other, a standing wave field was generated in the crossing region. Changing the mutual phase of transmitting signals between the transducers, the sound field was shifted laterally, keeping the same form. When polystyrene particles were poured with a pipette into the sound field, they were trapped at the nodes of the sound-pressure distribution and were transported stably. Using three transducers whose sound-beam axes were crossed at an angle of 120° to each other in a plane, a standing wave field was generated with a hexagonal node pattern, and two-dimensional manipulation of a particle was accomplished.

Soliton interaction for a nonlinear discrete double chain

We investigate solution behavior with an emphasis on the localization of a double chain built up from two coupled one-dimensional Ablowitz-Ladik (AL) lattices. Whereas each one-dimensional AL lattice is completely integrable, the AL-type coupling between them causes the system to become nonintegrable. With regard to the stationary system we present a rigorous proof of its nonintegrability by means of the Melnikov method. Concerning stationary localized states, we identify the parameter regions for which the origin of the stationary map represents a hyperbolic equilibrium point. We show the existence of transversal intersections of the stable and unstable manifolds of the hyperbolic point. The associated homoclinic orbit is used to excite standing bright two-soliton-like excitations on the double chain. We compute both, analytically as well as numerically, the dynamical energy exchange rate between the two AL strings when on each of them a single AL soliton is launched. It is shown that the soliton interaction depends on the distance between the solitons and their mutual phase relation. There exist distinct energy exchange regimes ranging from suppressed to pronounced energy exchange. In the latter case directed energy flow from one chain into the other takes place. Eventually almost all energy is stored in a single chain in the form of a breather solution showing a bias toward one-dimensional coherent excitation patterns. In general, the single solitons from the integrable limit with no mutual coupling survive as moving breathers under the action of the nonintegrable coupling, and thus experience no lattice pinning. The only pinned solution we obtained resulted from the homoclinic orbit derived from the stationary system. As an interesting dynamical feature we observe that a single soliton may split into two moving breathing states of different amplitudes as well as different velocities.

Generation of phase-coherent laser beams for Raman spectroscopy and cooling by direct current modulation of a diode laser

A setup for generation of GHz side-bands by direct current modulation of a diode laser is described. The first order side-bands are used to inject two slave power diode lasers, in order to produce phase coherent, controllable frequency shifted, light beams, the mutual phase coherence of which has been verified (beat-note FWHM of 1 Hz, instrumentally limited). Some possible applications in the context of laser Raman cooling of cesium atoms are briefly discussed.

First demonstration of χ(2) grating encoding function in optical fibers

A new phenomenological model of self-organized second-harmonic generation is proposed describing the photoinduced χ (2) grating formation as a cumulative third-order nonlinearity via a complex χ (2) encoding function. The theoretical results attained are confronted with recent experimental measurements by Lambelet and Feinberg [Optics Lett. 21 (1996) 925] and the χ (2) encoding function is constructed for this special case. It is also shown that the efficiency of second-harmonic-generation preparation process is closely related with the mutual phase shift between the second-harmonic radiation generated and the second-harmonic seed, which is dependent upon the light intensities of shaping radiation and varies in the course of χ (2) writing process. The self-organized parametric down conversion with strong second-harmonic seeding being above the saturation value is proposed for an effective χ (2) grating formation.

Spatially resolved detection of phase locking in Josephson junction arrays

Abstract Two-dimensional arrays of shunted Nb/AlOx/Nb Josephson junctions have been investigated. Shapiro steps in the current–voltage ( I – V ) curve of an on-chip detector junction can be used to sense mutual phase locking of the array junctions. By scanning the array with a low-power electron beam, the phase locked junctions remain locked, whereas the unlocked junctions generate a beam-induced additional voltage drop along the array. In regions of the array’s bias current where pronounced Shapiro steps occur in the detector’s I – V curve, practically no array junction generates a beam-induced voltage signal, thus indicating complete mutual locking. For other bias currents of the array with less than maximum detected power, some of the junctions generate beam-induced signals, and can be identified as being non-locked. Our investigations allow a detailed and spatially resolved analysis of mutual phase locking in arrays of Josephson junctions. Moreover, the results obtained with autonomous arrays are compared to experiments performed with injection locked arrays.

Multiple-valuedc-axis critical current and phase locking inBi2Sr2CaCu2O8+δsingle crystals

We have experimentally found that the temperature dependence of the critical current in the $c$-axis direction, ${I}_{c}(T),$ of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ (Bi2212) single crystals may have multiple branches. At a given temperature, the probability distribution function ${P(I}_{c})$ for leaving the zero-voltage state may therefore have several maxima, each corresponding to a particular branch of ${I}_{c}(T).$ We have modeled the ${I}_{c}(T)$ for Bi2212, considering it as a stack of intrinsic Josephson junctions (JJ's). The numerical simulations are in qualitative agreement with the experiment. We argue that the existence of different quasiequilibrium fluxon modes in stacked JJ's may be a reason for the multiple-valued ${I}_{c}$ that is observed in the experiments. Mutual phase locking of junctions, resulting in an increased ${I}_{c}(T),$ is observed.

The relationship between coherent structures and heat transfer processes in the initial region of a round jet

This paper describes an experimental study of the relationship between coherent vortical structures and the intensity of heat transport in the initial region of a round, free jet. Simultaneous measurements of velocity and temperature were taken with a four-wire combined probe in a jet that was acoustically stimulated with a frequency corresponding to the jet-column mode. The obtained results suggest that the mutual phase relations between oscillatory and random components of velocity and temperature lead to substantial intensification of the radial heat transport. Due to the same reason the longitudinal heat flux does not reveal a significant change in the presence of coherent structures and, as a result, a much wider spread of the temperature field in comparison with velocity may be observed as a characteristic feature of this flow. It was also observed that heat transfer processes are realized in substantial part by random turbulence generated due to the action of coherent motion.

On the puzzling phase of second-harmonic light generated in self-prepared frequency doubling fibres

The evolution of mutual phase shift between the second-harmonic seeding light and the second-harmonic light produced by the photo-induced non-linearity in optical fibre in the course of the fibre preparation process is computed using the data of Lambelet–Feinberg's experiment. It is shown that this mutual phase shift monotonously decreases from its initial value, which depends upon the light intensities of the fundamental pump and second-harmonic seeding radiations, and approaches −π/2 in the saturation state. A simple phenomenological model is proposed that describes the formation of a photo-induced χ(2) grating by means of a complex rate coefficient β, which is dependent upon the light intensities of shaping radiation and varies in the course of the χ(2) writing process. The self-organized parametric down-conversion with strong second-harmonic seeding being above the saturation value is proposed for an effective χ(2) grating formation.

Wavebeam Multiplication Phenomena to RF Power Distribution Systems of High-Energy Linear Accelerators

A new quasi-optical concept of electrically proof Delay Line Distribution System (DLDS) for high-energy electron/positron accelerators is proposed. In order to increase microwave power, used for particle acceleration, the concept assumes summing up of a few wavebeams in multimode rectangular waveguide. Operating by mutual phases of the wavebeams, to be produced by coherent sources, the system allows also a distribution of long multiplied RF pulses on a set of acceleration sections. Calculations of key components are fulfilled at 34 GHz frequency.

Mutual phase locking on resonant flux-flow steps in stacked long Josephson junctions

We demonstrate that, independently biasing the junctions in a two stack in the resonant flux-flow regime, we can obtain mutual locking in four different states. Two of them possibly consist of out-of-phase Josephson oscillations and two consist of in-phase oscillations. They are found experimentally to be very stable for a quite large range of applied magnetic field.

Phase-coherent light pulses for atom optics and interferometry

We have developed a novel source for the generation of powerful phase-coherent light pulses. Our setup uses an acousto-optic modulator (AOM) inside an external high-finesse resonator. By applying a short rf pulse to the AOM, we dump the cavity and extract a large part of the stored and enhanced power within a short optical pulse and with a controllable optical phase. In preliminary experiments we reached 100 W of peak power in a 15-ns optical pulse. The mutual phase coherence of successive light pulses is demonstrated with a molecular iodine interferometer experiment in a cell.

Plasma biasing by radial electric fields induced in front of lower hybrid grills via poloidal ponderomotive forces

This article treats the stationary radial electric field that the lower hybrid wave induces in front of the grill of the exciting antenna structure. The source of the induced electric field is the poloidal ponderomotive force of lower hybrid waves. It is shown that electric fields of the order of tens of volts per cm are possible in tokamak discharges. The required poloidal ponderomotive force would be possible if the mutual phasing of the horizontal waveguide rows of the grill were of a suitable value. It has been found that the induced radial electric field and the associated poloidal and toroidal plasma rotation will undergo sign changes if the poloidal phasing of the grill is altered appropriately.

Phase and frequency shifts in a population of phase oscillators

We investigate the synchronization behavior of a population of globally coupled phase oscillators with randomly distributed eigenfrequencies. A variety of synchronized states is rigorously analyzed by means of the center manifold theorem combined with a nonlinear renormalization procedure. This way, the different synchronized states are determined explicitly. We observe $n$-cluster states, where $n=1,\dots{},4$. In a synchronized state all oscillators have the same frequency. Synchronization frequency and mutual phase differences depend on model parameters as well as on the configuration of the synchronized state, i.e., the number of oscillators within each cluster. The synchronization frequency may decisively differ from the mean of the eigenfrequencies, e.g., giving rise to frozen states, which are synchronized states with vanishing synchronization frequency. Unstable cluster states are associated with transitions between different synchronization frequencies. Our approach can easily be extended to a population of oscillators with randomly distributed coupling strengths. The different synchronized states are discussed in the context of neural coding.

Intrinsic mechanism of phase locking in two-dimensional Josephson junction networks in presence of an external magnetic field

We present numerical simulations of the dynamics of two-dimensional Josephson junction arrays to study the mechanism of mutual phase locking. We show that in the presence of an external magnetic field two mechanisms are playing a role in phase locking: feedback through the external load and internal coupling between rows due to microwave currents induced by the field. We have found the parameter values (junction capacitance, cell loop inductance, impedance of the external load) for which the interplay of both these mechanisms leads to the in-phase solution. The case of unloaded arrays is discussed as well.