Analysis of radiation-pressure induced mechanical oscillation of an optical microcavity

The theoretical work of Braginsky predicted that radiation pressure can couple the mechanical, mirror eigenmodes of a Fabry-Pérot resonator to its optical modes, leading to a parametric oscillation instability. This regime is characterized by regenerative mechanical oscillation of the mechanical mirror eigenmodes. We have recently observed the excitation of mechanical modes in an ultrahigh Q optical microcavity. Here, we present a detailed experimental analysis of this effect and demonstrate that radiation pressure is the excitation mechanism of the observed mechanical oscillations.     

Radial magnetosonic eigenmodes in a toroidal plasma with an ion-ion hybrid layer

The conditions for excitation of a standing magnetosonic wave structure in the region between the ion-ion hybrid cut-off layer and an antenna situated near the wall on the outside of a toroidal plasma have been derived. It is shown that low-order radial eigenmodes may be excited under usual conditions, but the order of the mode increases as the plasma density and its size increase. Such radial eigenmodes are shown to be more easily tracked than the usual magnetosonic toroidal eigenmodes.     

Quantum corrals, eigenmodes, and quantum mirages in s-wave superconductors

We study the electronic structure of magnetic and nonmagnetic quantum corrals embedded in two-dimensional s-wave superconductors. We demonstrate that a quantum mirage of an impurity bound state is projected from the occupied into the empty focus of a nonmagnetic quantum corral via the excitation of the corral's eigenmodes. We show that quantum corrals provide a new tool for manipulating the interaction between magnetic impurities by exciting oscillations in the corral's impurity potential. Finally, we discuss the form of eigenmodes in magnetic quantum corrals.     

Self-consistent nonlinear analysis of overmoded gyrotron oscillators

The self-consistent nonlinear analysis is presented for an overmoded gyrotron, in which the gyrotropic beam interacts with more than one cavity eigenmodes. The nonlinear equations are obtained in the slow time scale for the motion of each individual particle and for the evolution of the amplitude and frequency of each individual cavity eigenmode. A numerically efficient algebraic longtime-step algorithm is developed, which includes magnetostatic field tapering and time transients. Numerical examples are presented for the excitation and competition of the cavity eigenmodes.Work supported by the U.S. Naval Research Laboratory, Plasma Physics Division, under Contract No. N00173-79-C-0200.     

Integration of optical pulses by resonant diffraction gratings

The possibility of integrating optical pulses by resonant diffraction gratings has been considered. It has been shown that a diffraction grating provides integration of the pulse envelope in the vicinity of quasiguided-mode resonances. The integration is performed with an exponential weight function, whose decay rate is deter-mined by the quality factor of the resonance. Metallic diffraction gratings for integration of picosecond pulses have been computed. The calculation of the grating eigenmodes with the use of the scattering-matrix method has shown that the integration is performed in the vicinity of the resonances corresponding to the excitation of surface plasmon polaritons at the grating boundary. According to the results of numerical simulation, the integration quality is quite high.     

Spin remagnetization excitations in semiconductors with Rashba and Dresselhaus spin–orbit coupling

Spin remagnetization modes in paramagnetic materials with Rashba and Dresselhaus spin–orbit interaction are studied by analytically solving the kinetic equations for the spin-density matrix. These eigenmodes, which are induced by an in-plane electric field, lead to a rotation of the spin magnetic moment. The specific character of the spin remagnetization modes depends on the details of the excitation mechanism. By applying the approach to another system, namely to a model for graphene, pseudospin excitations are identified.     

Theory of space-charge waves in semiconductors with negative differential conductivity

Phenomena that accompany optical excitation of eigenmodes of electron gas oscillation in semiconductors with an N-shaped current-voltage (I-U) characteristic in a strong electric field are investigated theoretically. The dependence of the current flowing through a sample on the oscillation frequency of the interference pattern of light illuminating the sample is analyzed. Nonsteady-state and nonuniform illumination produces an internal electric field, which interacts resonantly with the eigenmodes when the oscillation frequency of the interference pattern coincides with an eigenfrequency of electronic gas oscillation. As the maximum of the I-U curve is approached, the interaction becomes nonlinear in character.     

On the resonant scattering at guide dielectric windows

The effect of output wave resonant scattering at vacuum window of a microwave device caused by high-quality dielectric window eigenmodes excitation is studied. These negative resonant effects can seriously influence the device operation. The numerical calculation results are confirmed by a model experiment.     

A WAVENUMBER APPROACH TO MODELLING THE RESPONSE OF A RANDOMLY EXCITED PANEL, PART I: GENERAL THEORY

Part I of this paper presents a self-contained analytical framework for determining the vibro-acoustic response of a plate to a large class of random excitations. The wavenumber approach is used, which provides an insight into the physical properties of the panel response and enables us to evaluate efficiently the validity of several simplifying assumptions. This formulation is used in Part II for predicting the statistical response of an aircraft panel excited by a turbulent boundary layer. In this paper, we first provide a general statement of the problem and describe how the spectral densities of the panel response can be obtained from an analysis of the system response to a harmonic deterministic excitation and a statistical model for the forcing field. The harmonic response of the system is then expanded as a series of the eigenmodes of the fluid-loaded panel and these fluid-loaded eigenmodes are approximated by a perturbation method. Then, we evaluate the conditions under which this series simplifies into a classical modal formulation in terms of the in vacuo eigenmodes.To illustrate the use of a wavenumber approach, we consider three examples, namely, the vibro-acoustic response of a panel excited by an incidence diffuse acoustic field, by a fully developed turbulent flow and by a pressure field which is spatially uncorrelated from one point to another. Convergence properties of the modal formulations are also examined.     

Magnetic response of planar dielectric rings

Magnetic response of a planar dielectric ring to an axially applied time-harmonic magnetic field is analyzed. We find the self-consistent distribution of the polarization current in the ring and its magnetic moment. It is shown that the magnetic moment exhibits multiple resonances corresponding to the excitation of different eigenmodes in the ring. The properties of the fundamental eigenmode are used to analyze the performance and limitations of an equivalent LCR circuit model.     

磁绝缘线振荡器中模式竞争问题的数值模拟

为理解磁绝缘线振荡器(MILO)实验中频频出现的模式竞争问题,利用3维全电磁粒子模拟程序对C波段MILO的实验模型进行研究,探索各种非对称激励机制对产生微波模式的影响,结果显示:阴极电子随机发射、电压的慢上升前沿、较低的电压等因素都可导致非对称高阶模式的产生,并使输出微波功率大大降低。模拟计算得出MILO中存在频率为3.6 GHz左右的基模和频率分别为3.7,4.1,4.6 GHz左右的3种高阶模式,与Karat计算结果基本一致。     

Generation of Coupled Modes in an Unmatched Three-Mirror Laser Cavity

An extraordinary phenomenon of generation of coupled types of oscillations with a transverse field distribution corresponding to the ТЕМ _pq eigenmodes with different pairs of indices p and q in the main laser cavity and in an external cavity has been experimentally detected. The excitation of coupled modes depends on the configuration and tuning of partial cavities. To solve the system of integral equations for a three-mirror cavity with mismatched spherical mirrors in the quasioptical approximation, it has been proposed to use modified boundary conditions including the coupling coefficients for eigenmodes in partial cavities.     

Noninvasive protein structural flexibility mapping by bimodal dynamic force microscopy

Mapping of the protein structural flexibility with sub-2-nm spatial resolution in liquid is achieved by combining bimodal excitation and frequency modulation force microscopy. The excitation of two cantilever eigenmodes in dynamic force microscopy enables the separation between topography and flexibility mapping. We have measured variations of the elastic modulus in a single antibody pentamer from 8 to 18 MPa when the probe is moved from the end of the protein arm to the central protrusion. Bimodal dynamic force microscopy enables us to perform the measurements under very small repulsive loads (30-40 pN).     

Impurity-induced local modes in one-dimensional dusty plasma chains

The effects of impurity on eigenmodes in one-dimensional dusty plasma lattices are studied.It is found that local modes can be excited besides lattice waves,due to the existence of an impurity particle.The dispersion relations of the modes are derived accordingly.Properties of the lattice and local modes are also analyzed and discussed,particularly for their symmetric features and conditions of the mode excitation.     

The influence of spread of excitation on the detection of amplitude modulation imposed on sinusoidal carriers at high levels

The improvement in amplitude modulation (AM) detection thresholds with increasing level of a sinusoidal carrier has been attributed to listening on the high-frequency side of the excitation pattern, where the growth of excitation is more linear, or to an increase in the number of "channels" via spread of excitation. In the present study, AM detection thresholds were measured using a 1000-Hz sinusoidal carrier. Thresholds for modulation frequencies of 4-64 Hz improved by about 10-20 dB as the carrier level increased from 10 dB SL (14.5 dB SPL on average) to 80 dB SPL. To minimize the use of spread of excitation with an 80-dB carrier, tonal "restrictors" with frequencies of 501, 801, 1210, and 1510 Hz were used alone and in combination. High-frequency restrictors elevated AM detection thresholds, whereas low-frequency restrictors did not, indicating that excitation on the high side is more important for detecting AM. Results of modeling suggest that the improvement in AM detection thresholds at high levels is likely due to the use of a relatively linear growth of response on the high-frequency side of the excitation pattern.     

Fundamentals and model of photonic-force microscopy

Exact calculations of the near-field electromagnetic force on a nanoparticle exerted by the presence of a corrugated dielectric interface are carried out. The illumination of this system excites the particle eigenmodes. The calculation is two-dimensional, so the nanoparticle is actually a nanocylinder that scans parallel to the interface. This system constitutes a model of force transduction and surface topography imaging for a photonic-force microscope with signal enhancement owing to morphological resonance excitation of the probe.     

JT-60U ��JT-60SA ���������¸��������Ӽ�������ɢ�����ұ���ģ

运用线性回旋动力学与磁流体力学的混合模拟程序,研究了JT-60U和JT-60SA装置中高能量粒子对离散阿尔芬本征模的共振激发.发现了丰富的αTAE动力学不稳定模式,研究了它的不稳定特性对高能量粒子速度的依赖关系.发现在JT-60U高βp ELMy H模运行中有grassy ELM的放电比有gaint ELM的放电更容易被高能量粒子激发成不稳定模式,在有边缘L模存在的负剪切运行下的各个势阱中都存在高能量粒子激发的αTAE不稳定模式.另外在JT-60SA中高βp全非感应电流驱动下的模拟实验放电下也发现了丰富的αTAE不稳定模式,观察了αTAE在该装置中沿磁场线和径向两个方向的二维广域本征模特性.     

Resonance breakdown of a Coulomb blockade due to the mechanical vibrations of a quantum dot

The effect of forced mechanical vibrations of a suspended single-electron transistor on Coulomb-blockade limited electron tunneling through a quantum dot has been studied. The mechanical vibrations of the quantum dot have been shown to result in the Coulomb blockade breakdown, which is manifested by narrow resonance peaks of the transistor conductance as a function of the excitation frequency at the frequencies corresponding to the eigenmodes of the mechanical vibrations. The mechanism of the observed effect presumably associated with the oscillations of the mutual electrical capacitances between the quantum dot and the surrounding electrodes is discussed.     

Excitations of thermoelastic waves in plates by a pulsed laser

The method of the eigenfunction expansion, also known as the expansion in normal modes, is employed to study numerically the axisymmetric excitation of the thermoelastic waves in plates by a pulsed laser. This method gives a systematic treatment and allows one to investigate not only the quasistatic and dynamic thermoelastic responses of pulsed photothermal deformation on the time scale of 1 s, but also the thermoelastic generation of longitudinal, transverse, and surface acoustic waves in thick materials, as well as the excitations of the Rayleigh-Lamb wave modes in thin plates. The formalism is particularly suitable for waveform analyses of the excitations of transient Lamb waves in thin plates because one needs only to calculate the contributions of several lower eigenmodes. The numerical technique provides a quantitative tool for the experimental determination of material properties, especially the mechanical and elastic properties of free-standing films and thicker sheet materials by thermoelastic detection.     

加速100 mA质子束的低β超导半波长谐振腔内的高阶模（英）

基于超导器的连续波运行的高流强质子/氘束被越来越多的大科学装置所采用。在流强低于10 mA情况下,用于加速低段粒子的超导腔的高阶模影响基本可以忽略,但是对于加速百mA强流的低超导腔,其高阶模损耗情况有待研究。近期北京大学设计并加工了一支=0.09、运行频率162.5 MHz的超导半波长谐振腔,用于研究非相对论低超导半波长谐振腔加速100 mA强流质子束时可能涉及到的关键物理问题。重点研究了这支半波长谐振腔内部高阶模损耗的问题,用时域和频域两种方法分别计算了腔的高阶模损失因子,同时计算了考虑加工误差下腔内发生高阶模共振激发的概率。