Magnetic quantum dot: a magnetic transmission barrier and resonator

We study the ballistic edge-channel transport in quantum wires with a magnetic quantum dot, which is formed by two different magnetic fields B(*) and B0 inside and outside the dot, respectively. We find that the electron states located near the dot and the scattering of edge channels by the dot strongly depend on whether B(*) is parallel or antiparallel to B0. For parallel fields, two-terminal conductance as a function of channel energy is quantized except for resonances, while, for antiparallel fields, it is not quantized and all channels can be completely reflected in some energy ranges. All these features are attributed to the characteristic magnetic confinements caused by nonuniform fields.     

Magnetic resonance in an atomic vapor excited by a mechanical resonator

We demonstrate a direct resonant interaction between the mechanical motion of a mesoscopic resonator and the spin degrees of freedom of a sample of neutral atoms in the gas phase. This coupling, mediated by a magnetic particle attached to the tip of the miniature mechanical resonator, excites a coherent precession of the atomic spins about a static magnetic field. The novel coupled atom-resonator system may enable development of low-power, high-performance sensors, and enhance research efforts connected with the manipulation of cold atoms, quantum control, and high-resolution microscopy.     

Magnetic modes in a resonator built around a circular evanescent waveguide and coaxial line

The eigenfrequencies of magnetic modes in a resonator made up of two segments of a circular evanescent waveguide and a coaxial line are found by solving an electrodynamic problem. For the fundamental H_11dH_{11\delta } mode, the performance of the resonator is studied analytically and experimentally over a wide range of its parameters. The feasibility of a high-power microwave semiconductor oscillator based on the resonator under study is demonstrated.     

Magnetic response of split ring resonator metamaterials: From effective medium dispersion to photonic band gaps

On systematically investigating the electromagnetic response of periodic split-ring resonator (SRR) metamaterials as a function of the size-to-wavelength (a/λ) ratio, we find that the stop bands due to the geometric resonances of the SRR weaken with increasing (a/λ) ratio, and are eventually replaced by stop bands due to Bragg scattering. Our study traces the behaviour of SRR-based metamaterials as the resonance frequency increases and the wavelength of the radiation finally becomes comparable to the size of the unit cell of the metamaterial. In the intermediate stages, the dispersion of the SRR metamaterial can still be described as due to a localized magnetic resonances while Bragg scattering finally becomes the dominant phenomenon as a/λ∼1/2.     

Spatial resonator solitons

Spatial solitons can exist in various kinds of nonlinear optical resonators with and without amplification. In the past years different types of these localized structures such as vortices, bright, dark solitons, and phase solitons have been experimentally shown to exist. Many links appear to exist to fields different from optics, such as fluids, phase transitions, or particle physics. These spatial resonator solitons are bistable and due to their mobility suggest schemes of information processing not possible with the fixed bistable elements forming the basic ingredient of traditional electronic processing. The recent demonstration of existence and manipulation of spatial solitons in semiconductor microresonators represents a step in the direction of such optical parallel processing applications. We review some proof of principle soliton experiments on slow systems, and describe in more detail the experiments on semiconductor resonator solitons which are aimed at applications.     

Dual Helmholtz resonator

Acoustic characteristics of a dual Helmholtz resonator which consists of a pair of cylindrical neck and cavity connected in series (neck-cavity-neck-cavity) are established primarily in terms of a lumped-parameter theory. The results are then compared to (a) a two-dimensional analytical approach by applying a pressure/velocity matching technique for a piston-driven model; (b) a three-dimensional boundary element method for a pipe-mounted model; and (c) experiments on an impedance-tube test setup with one fabricated prototype installed in a sidebranch orientation (pipe-mounted model). Closed-form expressions have been developed in the present study for the resonance frequencies and the transmission loss of this two degree-of-freedom system based on the Newton’s second law of motion for a lumped system. The resonance frequencies and the transmission loss from this theory agree well with the analytical results, while showing a reasonable comparison with both the numerical predictions and the measurements.     

Sensitivity of surface resistance measurement of HTS thin films by cavity resonator, dielectric resonator and microstrip line resonator

Microwave surface resistance (R _s) of silver-doped YBa₂Cu₃O_7-δ (YBCO) thin film, deposited by laser ablation technique on 10 mm × 10 mm LaAlO₃ substrate, has been measured by resonant techniques in the frequency range from 5 GHz to 20 GHz. The geometrical factor of the sample and the resonator has been determined theoretically by the knowledge of the electromagnetic field distribution in the resonators. The microwave surface resistance of the superconducting sample is then extracted from the measured Q value as a function of temperature. The sensitivity of the R _s measurement, that is, the relative change in the Q value with the change in the R _s value is determined for each resonator.     

Diffraction losses of an asymmetric stable laser resonator using an equivalent resonator

An asymmetric stable laser resonator with one large mirror and the other mirror apertured is considered. An equivalent symmetric resonator is derived which enables the determination of the theoretical diffraction losses from Li's computations. Experiments are done to test the validity of the predictions. The experimental diffraction losses agree very well with the theoretical values and the usefulness of the concept of equivalent resonator is therefore confirmed.     

Germanium microsphere high-Q resonator

In this Letter, the fabrication and characterization of a microsphere resonator from the semiconductor germanium is demonstrated. Whispering gallery modes are excited in a 46 μm diameter germanium microsphere resonator using evanescent coupling from a tapered silica optical fiber with a waist diameter of 2 μm. Resonances with Q factors as high as 3.8×10(4) at wavelengths near 2 μm are observed. Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, in particular at long wavelengths, such as around 2 μm.     

Single-input spherical microbubble resonator

A single-input whispering gallery optical microbubble resonator is presented. Spherical microbubbles with diameters less than 100 μm, micrometer-sized wall thicknesses, and a single opening or input were fabricated by heating the tapered tip of a pressurized glass capillary using a CO(2) laser. Optical whispering gallery modes with Q factors of ～10(5) were obtained. The bubbles were filled with water and mode shifts of ～20 GHz were observed. Fano-type resonances were detected when the coupling optical fiber diameter was less than 1 μm, causing the microresonator to switch from being a band-stop filter to a bandpass filter. Larger bubbles with submicrometer wall thickness were also fabricated.     

On the Helmholtz resonator

This paper develops the theory of the excitation of a Helmholtz resonator by external disturbances located arbitrarily close to the mouth of the resonator. The classical approach of Rayleigh is thereby extended to situations in which the disturbance at the mouth is not necessarily equivalent to a uniform, time dependent pressure perturbation. The analysis involves the derivation of the Green function of the resonator in a manner similar to that described in an earlier paper. The use of the Green function is illustrated by two examples in which the resonator is excited by a low Mach number stream of air. In the first case the air stream has a periodic large scale structure such as may be caused by a Kelvin-Helmholtz type of instability. The second example models the case of excitation by a shear layer possessing a continuous spectrum of turbulent eddies. In both of these applications the orders of magnitude of the sound pressure levels involved are illustrated for a typical resonator.     

A differential graphene-based resonator

We describe a new, in principle, layout of a graphene resonator—a differential resonator, which makes it possible to increase substantially its sensitivity to the mass deposited on it. The differential resonator consists of two parallel graphene films, which are fastened in insulating supports; the lower film is arranged over the conducting surface. The force coupling between the films is performed by the electrostatic field in the space between them. Several equilibrium positions are possible in such a mechanical system. Small free oscillations near the stable equilibrium position are considered. The field strength is selected so that the mechanical system of two graphene films would have two close eigenfrequencies. The free oscillations of such a system have the form of intrinsic frequencies of the system much lower that the partial frequency of each film. When depositing the particle on the upper film, the partial eigenfrequency of this film decreases. In this case, the characteristic envelope frequency also decreases, and a small variation in the partial eigenfrequency leads to considerable variation in the characteristic envelope frequency. This provides higher sensitivity to the mass of the revealed particle for the differential resonator compared with the resonator based on one film.     

深度热稳定望远镜腔

本文从理论上详细讨论了当g~*参数满足条件g_1~*g_2~*=1/2的望远镜腔的深度热稳特性.解析地推导出补偿热扰的望远镜失调量(?)的精确表示式.并且证明,采用适当的假设,就可从精确公式推导出文献[4,5]中失调量(?)的简化近似公式.计算机模拟和数值计算证实了我们的理论结果,并给出光斑大小随望远镜腔参数变化的曲线.     

Photonic-band-gap resonator gyrotron.

We report the design and experimental demonstration of a gyrotron oscillator using a photonic-band-gap (PBG) structure to eliminate mode competition in a highly overmoded resonator. The PBG cavity supports a TE(041)-like mode at 140 GHz and is designed to have no competing modes over a minimum frequency range delta omega/omega of 30% about the design mode. Experimental operation of a PBG gyrotron at 68 kV and 5 A produced 25 kW of peak power in the design mode. No other modes were observed over the full predicted operating range about the design mode. PBG cavities show great promise for applications in vacuum electron devices in the millimeter- and submillimeter-wave bands.     

The degenerate multimode confocal resonator

The simultaneous excitation of the fundamental and higher order radial modes in a degenerate confocal resonator leads to destructive interference between modes on the optic axis and hence reduces the power coupled by an axial iris. This mode competition may be reduced drastically by proper control of the aperture flux distribution and is of particular significance when the resonator is used for the power combining of solid-state sources.     

A simple ring resonator system

A simple technique for the alignment of a three mirror ring cavity system is described. It is also shown that walk-off and astigmatism problems can be eliminated with relative ease, providing notable advantages over alternative travelling wave cavity configurations.     

一种新型巨脉冲锁模激光器谐振腔

利用变换圆图解分析方法,分析了一种新型锁模激光谐振腔,它不同于通常Ti宝石锁模激光谐振腔,在这种新型锁模激光谐振腔中使用了分离的激活介质与克尔介质,可输出能量达23mJ的基频脉冲序列以及13.5mJ的倍频脉冲序列。