Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the <Emphasis Type="Italic">c</Emphasis>-axis

We studied a response of Bi-2212 mesa type structures to 100 GHz microwave radiation. We found that applying magnetic field of about 0.1 T across the layers enables to observe collective Shapiro step response corresponding to a synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At high microwave power we observed up to 10th harmonics of the fundamental Shapiro step. Besides, we found microwave induced flux-flow step position of which is proportional to the square root of microwave power and that can exceed at high enough powers 1 THz operating frequency of IJJ oscillations. The article is published in the original.     

Area scintillations of Bessel Gaussian and modified Bessel Gaussian beams of zeroth order

As an extension of our previous study, the area scintillation aspects of Bessel Gaussian and modified Bessel Gaussian beams of zeroth order are investigated. The analysis is carried out on the basis of equal source sizes and equal source powers. It is found that, when compared on equal source size basis, modified Bessel Gaussian beams always have less area scintillations than a Gaussian beam, while Bessel Gaussian beams exhibit more area scintillations. Comparison on equal source power basis, however, removes the advantage of modified Bessel Gaussian beams, that is, their area scintillations become nearly the same as those of the Gaussian beam. On the other hand, for the case of equal source powers, Bessel Gaussian beams with larger width parameters continue to have higher area scintillations than the Gaussian beam. We provide graphical illustrations for profiles of equal source size beams, equal source power beams and the curves to aid the selection of equal source power beams.     

The role of linear power partitioning in beam filamentation

We demonstrate through computer simulation that power partitioning due to linear diffraction can play a crucial role in the break up of high intensity apertured beams propagating in air. By investigating the way linear diffraction partitions power in these beams, we are able to predict the positions and relative powers of supercritical hot spots. PACS 42.65.k; 42.65.Jx     

From avalanches to fluid flow: A continuous picture of grain dynamics down a heap

Surface flows are excited by steadily adding spherical glass beads to the top of a heap. To simultaneously characterize the fast single-grain dynamics and the much slower collective intermittency of the flow, we extend photon-correlation spectroscopy via fourth-order temporal correlations in the scattered light intensity. We find that microscopic grain dynamics during an avalanche are similar to those in the continuous flow just above the transition. We also find that there is a minimum jamming time, even arbitrarily close to the transition.     

Interaction of counterpropagating discrete solitons in a nonlinear one-dimensional waveguide array

We experimentally investigate the interaction of counterpropagating discrete solitons in a one-dimensional waveguide array in photorefractive lithium niobate. While for low input powers only weak interaction and formation of counterpropagating vector solitons are observed, for higher input powers a growing instability results in discrete lateral shifting of the formed discrete solitons. Numerical modeling shows the existence of three different regimes: stable propagation of vector solitons at low power, instability for intermediate power levels leading to discrete shifting of the two discrete solitons, and an irregular temporal dynamic behavior of the two beams for high input power.     

Surface acoustic wave controlled charge dynamics in a thin InGaAs quantum well

We experimentally study the optical emission of a thin quantum well and its dynamic modulation by a surface acoustic wave (SAW). We observe a characteristic transition of the modulation from one maximum to two maxima per SAW cycle as the acoustic power is increased which we find in good agreement with numerical calculations of the SAW controlled carrier dynamics. At low acoustic powers the carrier mobilities limit electron-hole pair dissociation, whereas at high power levels the induced electric fields give rise to efficient acousto-electric carrier transport. The direct comparison between the experimental data and the numerical simulations provide an absolute calibration of the local SAW phase.     

强非局域正交偏振双厄米高斯光束的传输特性

依据非局域非线性介质中双光束传输时遵循的非局域非线性薛定谔耦合方程,在强非局域情形下,通过把响应函数作泰勒展开近似取到二阶,运用变分法求出了正交偏振、中心重合的双厄米高斯光束在强非局域介质中传输时各参量演化规律和一个临界功率,并运用分步傅里叶算法数值模拟出了束宽和相位的演化规律。当两光束以临界功率入射时,得到了正交偏振、中心重合的双厄米高斯空间光孤子及其大相移演化规律。当两光束以总临界功率入射,但两束光的入射功率不等时,光束可以形成呼吸子,但随着阶数的增加呼吸子将越来越不稳定。对于各阶呼吸子,功率大的束宽都作周期性压缩振荡变化,功率小的束宽都作周期性展宽振荡变化,且两呼吸子中功率大的相移随传输距离增加更快。在厄米高斯光束阶数小于5时,变分解得到的结果与数值解吻合较好。     

Charge distribution on annealed polyelectrolytes

We investigate the equilibrium charge distribution along a single annealed polyelectrolyte chain under different conditions. The coupling between the conformation of the chain and the local charge distribution is described for various solvent qualities and salt concentration. In salt free solution, we find a slight charge depletion in the central part of the chain: the charges accumulate at the ends. The effect is less important if salt is added to the solution since the charge inhomogeneity is localized close to the chain ends over a distance of order of the Debye length. In the case of poor solvent conditions we find a different charge per monomer in the beads and in the strings in the framework of the necklace model. This inhomogeneity leads to a charge instability and a first order transition between spherical globules and elongated chains. Received 19 March 1999 and Received in final form 2 August 1999     

Thermally induced self-focusing and optical beam interactions in planar strontium barium niobate waveguides

We present an experimental study of thermally induced self-focusing effects and interactions of incoherent light beams in strontium barium niobate waveguides. Depending on the input power, a single parallel beam is strongly focused inside the sample up to diameters of several micrometers. For higher input power we observe the splitting of the beam in a sequence of several spots. We demonstrate that these thermally induced refractive-index patterns can be used to focus and deflect an incoherent guided probe beam in the waveguide with time constants below 1 ms.     

Morphology and scaling of impact craters in granular media

We present the results of experiments on impact craters formed by dropping a steel ball vertically into a container of small glass beads. As the energy of impact increases, we observe a progression of crater morphologies analogous to that seen in craters on the moon. We find that both the diameter and the depth of the craters are proportional to the 1/4 power of the energy. The ratio of crater diameter to rim-to-floor depth is constant for low-energy impacts, but increases at higher energy, similar to what is observed for lunar craters.     

Optical bistability at low light level due to collective atomic recoil

We demonstrate optical nonlinearities due to the interaction of weak optical fields with the collective motion of a strongly dispersive ultracold gas. The combination of a recoil-induced resonance in the high gain regime and optical waveguiding within the dispersive medium enables us to achieve a collective atomic cooperativity of 275+/-50 even in the absence of a cavity. As a result, we observe optical bistability at input powers as low as 20 pW. The present scheme allows for dynamic optical control of the dispersive properties of the ultracold gas using very weak pulses of light. The experimental observations are in good agreement with a theoretical model.     

Transmittance of partially coherent flat topped beam with circular and elliptical symmetry in turbulence

Average relative power transmittance is evaluated, for partially coherent flat topped beams with circular and elliptical symmetry, propagated through turbulent atmosphere. We have shown that for partially coherent flat topped beams with the mentioned symmetry, power transmittance is enhanced as the order of flat topped beam increase, but the full coherent one does not show this behavior. Also we have shown that there is a transition region (R_C) for full and partial coherent flat topped beams with circular and elliptical symmetry. We investigated the dependency of the power transmittance in turbulent media with respect to the structure constant.     

Colloid particles in the interaction field of a disclination line in a nematic phase

On the basis of linear hydrodynamics, we analyze the trajectory of particle-hedgehog systems, attracted by a -1/2 disclination (defect line) in a nematic liquid crystal. We show that, as with the interactions between like-particles, the interaction between a particle and a disclination has an electrostatic analogue, the splay replacing the electric field, except for the symmetry properties. The disclination thus attracts the beads along nonradial tracks and in a self-assembling process, or template mechanism, may build a microscopic necklace with them.     

Superpositions of Laguerre-Gaussian Beams in Strongly Nonlocal Left-handed Materials

We present beam solutions of the strongly nonlocal nonlinear Schrödinger equation in left-handed materials (LHMs). Different Laguerre-Gaussian (LG) necklace beams, such as symmetric and asymmetric single layer and multilayernecklace beams are created by the superposition of two single beams with different topological charges. Such superpositions are then propagated through LHMs, displaying linear diffraction. It is found that the superposition of two LG_nm beams with opposite topological charges does not show rotational behavior and that there exists rotation for other topological charge combinations. Our theory predicts that the accessible solitons cannot exist in LHMs.     

High-cooperativity coupling of electron-spin ensembles to superconducting cavities

Electron spins in solids are promising candidates for quantum memories for superconducting qubits because they can have long coherence times, large collective couplings, and many qubits could be encoded into spin waves of a single ensemble. We demonstrate the coupling of electron-spin ensembles to a superconducting transmission-line cavity at strengths greatly exceeding the cavity decay rates and comparable to the spin linewidths. We also perform broadband spectroscopy of ruby (Al?O?:Cr(3+)) at millikelvin temperatures and low powers, using an on-chip feedline. In addition, we observe hyperfine structure in diamond P1 centers.     

Accessible solitons in three-dimensional parabolic cylindrical coordinates

A class of self-similar beams, named three-dimensional (3D) spatiotemporal parabolic accessible solitons, are introduced in the 3D highly nonlocal nonlinear media. We obtain exact solutions of the 3D spatiotemporal linear Schrödinger equation in parabolic cylindrical coordinates by using the method of separation of variables. The 3D localized structures are constructed with the help of the confluent hypergeometric Tricomi functions and the Hermite polynomials. Based on such an exact solution, we graphically display three different types of 3D beams: the Gaussian solitons, the ring necklace solitons, and the parabolic solitons, by choosing different mode parameters. We also perform direct numerical simulation to discuss the stability of local solutions. The procedure we follow provides a new method for the manipulation of spatiotemporal solitons.     

“Spin-orbit deformation” in inelastic scattering of protons at medium energies

Distorted-wave Born-approximation calculations for medium-energy proton inelastic scattering to collective states, which use microscopic, spin-dependent optical potentials that properly describe proton elastic analyzing powers, show that inclusion of the deformation or collectivity of the spin-orbit term in the inelastic transition matrix element has an important effect on predictions for the available inelastic angular distributions and analyzing powers.     

Propagation of coupled dipole-mode beams in nonlocal thermal media

The mutual trapping of two dipole-mode beams is investigated numerically in nonlocal thermal media. Results show that the incoherent attraction of perpendicularly aligned dipole-mode beams can enhance the stability of their composite structure. When the powers of the dipole components are identical, the larger the power, the shorter the stable distance. While when the powers are different, the closer the powers, and the longer the stable distance. Furthermore numerical results proved that the coupled solitary structures exhibit stable propagation for much larger distances than the corresponding scalar cases.     

基于减反膜外腔反馈半导体激光器拉曼光的产生

通过直接对减反膜外腔反馈半导体激光器进行电流调制的方法,得到了两束位相锁定且频率差在6.0-9.3GHz范围内连续可调的激光,其中6.835和9.192GHz分别对应Rb⁸⁷和Cs¹³³原子基态超精细能级之间的频率差,激光功率分别可以达到6.87mW和5.09mW. 根据减反膜外腔反馈半导体激光器的特点,通过调整外腔腔长、激光器工作温度、电流以及所加射频调制信号的功率和频率,在调制频率小于等于4.0GHz时可以将载波完全压制. 调制频率大于4.0GHz时,虽不能将载波完全压制,但由于外腔与调制频率共振时对调制的增强也得到了调制深度很高的激光,并对其中的物理机理作了分析. 通过后续滤波等方法处理以后,该拉曼光源可以广泛应用到原子的量子操控中. 关键词： 受激拉曼光 高频调制 调制增强     

Competitive localization of vortex lines and interacting bosons

We present a theory for the localization of three-dimensional vortex lines or two-dimensional bosons with a short-ranged repulsive interaction which are competing for a single columnar defect or potential well. For two vortices we use a necklace model approach to find a new kind of delocalization transition between two different states with a single bound particle. This exchange-delocalization transition is characterized by the onset of vortex exchange on the defect for sufficiently weak vortex-vortex repulsion or sufficiently weak binding energy corresponding to high temperature. We calculate the transition point and order of the exchange-delocalization transition. A generalization of this transition to an arbitrary vortex number is proposed.