Critical slowing down in a bistable model with squeezed vacuum environment

Critical slowing down effect in a bistable model of a two-level atomic medium in a ring cavity and in contact with squeezed vacuum field is examined within the mean field approximations in the high-, low- and arbitrary-Q cavity cases. Depending on the squeezed vacuum field phase parameter, the time response to linear perturbation of the incident field near the swtiching-on point can be enhanced or reduced compared with the normal vacuum case. In the low-Q cavity case with atomic collisional broadening switching time is both increased and become insensitive to the phase of the squeezed vacuum field. Analytical expressions are given and analysed for the critical (extermal) values of the incident field. In the high-Q cavity, Gaussian field feature causes lesser-steep transition between the stable states in both the normal and squeezed vacuum cases.Received: 25 April 2004, Published online: 24 August 2004PACS: 42.65.Pc Optical bistability, multistability, and switching, including local field effects - 42.65.-k Nonlinear optics     

Compression of terahertz radiation in resonant systems with a quantum superlattice

It is shown theoretically that ultrashort terahertz electromagnetic pulses can be generated in resonant systems containing a quantum semiconductor superlattice. This effect is due to the compression of radiation incident on a cavity as a result of ultrafast self-modulation of the cavity Q factor upon cyclic switching of the superlattice from the screening to the transparent state in a pump field.     

Diffusion coupling between a barrel-shaped resonant cavity and a coaxial waveguide

We consider a resonant cavity in the form of a section of a weakly irregular metal tube coupled with a waveguide of larger cross section. Eigenmodes of such a cavity with frequencies close to the cutoff frequency are described by the inhomogeneous-string equation. The solution of this equation obtained by the variational technique leads to standard formulas for interaction between the cavity and an incident wave.     

Surface plasmon resonance and field confinement in graphene nanoribbons in a nanocavity

In this work, we demonstrate surface plasmon resonance properties and field confinement under a strong interaction between a waveguide and graphene nanoribbons (GNRs), obtained by coupling with a nanocavity. The optical transmission of a waveguide–cavity–graphene structure is investigated by finite-difference time-domain simulations and coupled-mode theory. The resonant frequency and intensity of the GNR resonant modes can be precisely controlled by tuning the Fermi energy and carrier mobility of the graphene, respectively. Moreover, the refractive index of the cavity core, the susceptibility χ⁽³⁾ and the intensity of incident light have little effect on the GNR resonant modes, but have good tunability to the cavity resonant mode. The cavity length also has good tunability to the resonant mode of cavity. A strong interaction between the GNR resonant modes and the cavity resonant mode appears at a cavity length of L₁ = 350 nm. We also demonstrate the slow-light effect of this waveguide–cavity–graphene structure and an optical bistability effect in the plasmonic cavity mode by changing the intensity of the incident light. This waveguide–cavity–graphene structure can potentially be utilised to enhance optical confinement in graphene nano-integrated circuits for optical processing applications.     

非线性波导腔耦合特性研究

对一种非线性波导耦合腔进行了理论和实验研究。研究表明,该系统的透过率随入射光强变化。对于不同的初始偏置、耦合区长度和入射功率系统具有微分放大、限幅、反常耦合和双稳运行等不同的响应。     

Determination of wavefront aberrations using a Fabry-Perot cavity

A new method for detecting wavefront aberrations using a Fabry-Perot cavity is described. A Fabry-Perot cavity transmits the cavity eigenmode which satisfies a resonance condition, while the other modes are reflected from the cavity. Utilizing this mode discrimination property, we can extract aberration components from incident aberrated light as reflected light from the cavity. Under the condition of a weak aberration, the amplitude profile of the reflected light can be approximated to the wavefront aberration. We can therefore determine the wavefront aberrations in a visualized form with the technique. We present the detection scheme and the first experimental verification of the technique. The detected aberration using this technique was in good agreement with the result on the basis of a conventional wavefront sensor.     

Dispersive photon blockade in a superconducting circuit

Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These nonresonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots. This work differs from previous efforts in that the cavity-qubit excitations retain a photonic nature rather than a hybridization of qubit and photon and provides the needed tolerance to disorder for future condensed matter experiments.     

Observation of a nonlinear mode in a cylindrical Fabry-Perot cavity

We report what is believed to be the first observation of a nonlinear mode in a cylindrical nonlinear Fabry-Perot cavity. The field enhancement from cavity buildup, as well as the large chi((3)) optical nonlinearity that is due to resonantly excited (85)Rb vapor, allows the nonlinear mode to form at low incident optical powers of less than 1 mW. The mode is observed to occur for both self-focusing and self-defocusing nonlinearity.     

等离子体用于腔体的雷达散射截面减缩的实验研究

利用荧光灯等离子体管覆盖金属腔体内壁,测量了筒状等离子体覆盖的金属腔体对电磁波的回波衰减。测试结果表明:金属圆筒内壁的等离子体能够有效吸收0.80~1.75 GHz波段的入射波,入射电磁波的回波衰减值为5~25 dB;当入射电磁波频率接近1.75 GHz时,回波衰减最为强烈,在入射角度为10°时,吸收峰值可达26.71 dB,因此选择合适的电磁波入射角度,能够使等离子体对微波的吸收达到峰值。理论分析了影响等离子体对电磁波衰减的主要因素。结果表明：等离子体可有效缩减腔体结构的雷达散射截面面积,因此在进气道等腔体结构的隐身方面具有一定的应用前景。     

Light Squeezing in a Fabry–Perot Cavity

A quantum mechanical model for the study of quadrature squeezing in radiation coming out of Fabry–Perot cavity containing nonlinear Kerr medium has been proposed. We have incorporated the vacuum fluctuations entering in the cavity through unused ports. The analysis has been applied to a sample of GaAs filled in the Fabry–Perot cavity and irradiated by an off-resonant Co:MgF₂ laser. Limitations on achievable squeezing due to incident pump power, interaction time, nonlinear coupling parameter and facet reflectivities have been discussed and it is seen that low reflectivity of front facet and high reflectivity of rear facet of the cavity produces substantial squeezing.     

Reciprocity principle-based model for shielding effectiveness prediction of a rectangular cavity with a covered aperture

According to the reciprocity principle, we propose an efficient model to compute the shielding effectiveness of a rectangular cavity with apertures covered by conductive sheet against an external incident electromagnetic wave. This problem is converted into another problem of solving the electromagnetic field leakage from the cavity when the cavity is excited by an electric dipole placed within it. By the combination of the unperturbed cavity field and the transfer impedance of the sheet, the tangential electric field distribution on the outer surface of the sheet is obtained. Then, the field distribution is regarded as an equivalent surface magnetic current source responsible for the leakage field. The validation of this model is verified by a comparison with the circuital model and the full-wave simulations. This time-saving model can deal with arbitrary aperture shape, various wave propagation and polarization directions, and the near-field effect.     

Influence of the cross-phase modulation effect on the polarization states of waves transmitted through a non-linear Fabry–Pe´rot cavity

An analysis of the influence of the cross-phase modulation effect on the polarization states of waves transmitted through a non-linear Fabry–Pe′rot resonator with a self- focusing and self-defocusing Kerr medium is presented. The case is considered of two plane waves with different wavelengths incident on a non-linear Fabry–Pe′rot cavity. It is shown that the polarization states of the transmitted waves change bistably or multistably and depend on the parameters of incident waves and the resonator. This revised version was published online in November 2006 with corrections to the Cover Date.     

Engineering Two-Mode Squeezed Vacuum Motional State of a Single Intracavity Trapped Ion

We propose to generate two-mode squeezed vacuum motional state of an intracavity trapped ion by taking the advantage of the dissipation of the cavity mode. At the first step, the steady and pure two-mode motional entanglement between two motional degrees of the cold ion is obtained by engineering the couplings of both the motional modes of the ion to the cavity field. Based on the first step, a two-mode squeezed vacuum motional state is then generated by manipulating the phases of the external laser pulses incident on the ion.     

Parametric scattering of high-frequency elastic waves by a small spherical cavity oscillating under the action of a Rayleigh wave

Scattering of high-frequency transverse and longitudinal plane waves incident on a spherical cavity located at a small depth under the surface of a half-space is considered. The cavity oscillates as a whole in the field of a low-frequency Rayleigh surface wave, the oscillation vectors of the longitudinal, transverse, and surface waves being coplanar. The cavity radius is assumed to be small compared to the wavelengths of the sounding wave and the pumping surface wave. The scattered compression and shear waves at the combination frequencies ω±Ω are calculated in the dipole approximation. Expressions obtained describe the qualitative behavior of the combination-frequency signal levels produced at the outputs of horizontally and vertically oriented geophones moving over the free surface of the elastic half-space.     

Resonance theory of elastic wave scattering from a cylindrical cavity

Resonant excitation of a fluid-filled cylindrical cavity in an elastic medium by an incident compressional wave is investigated on the basis of the resonance theory of nuclear scattering. It is shown that the scattering amplitude consists of a series of narrow resonances super-imposed upon, and interfering with, a broad background that corresponds to the scattering from an empty cavity. The resonances may be analyzed in a most enlightening fashion by studying them separately in each partial wave of the normal-mode series. They are seen to correspond to excitations of the eigenvibrations of the cavity fluid caused by a phase-match of “creeping waves”, similar to the “Regge poles” of nuclear physics.     

Polarization and amplitude optical multistability in a nonlinear ring cavity

The stimulation of a ring cavity filled with an isotropic medium with third order nonlinearity by plane monochromatic arbitrary polarized light is studied. An evolution of the stationary transmission with the change of the polarization of the incident light from circular to linear is discussed. For the linear polarized incident light additional branches of high transmission corresponding to elliptically polarized transmitted light and degenerating with respect to the rotation of the polarization vector are found. The stability of the stationary solutions is discussed. The possibility of the transmitted light polarization and intensity control by changing the polarization ellipticity degree of the incident light is shown.     

半导体微腔中腔模、重空穴激子模和轻空穴激子模耦合

采用传输矩阵方法利用半经典的线性色散模型,计算半导体微腔内同时存在重空穴激子、轻空穴激子时,在不同入射角度下的反射谱,同时,利用三简谐振子耦合模型计算了在不同入射角度下,腔模同时和重空穴激子模、轻空穴激子模耦合所形成的三支腔极化激元的能量,以及腔模、重空穴激子模、轻空穴激子模分别在三支腔极化激元中所占的权重,结果表明随着入射角的增加腔极化激元的高能支和两个低能支之间存在明显的反交叉现象,同时,腔模和重空穴激子模、轻空穴激子模在腔极化激元中所占的权重呈现增加或减小的趋势 关键词： 半导体微腔 腔极化激元 激子     

The absorptivity of a specularly reflecting cone for oblique angles of view

The absorptivity of a specularly-reflecting conical cavity is a function only of the number of reflections, n, undergone by an incident ray before it is reflected out again. A simple general expression for n is derived which applies to oblique incident rays as well as paraxial rays. It is shown that as the point at which the incident ray first strikes the conical surface moves from the rim towards the apex. a point is reached beyond which n increases by one.     

Enission spectra Of aΞ-type three-1evel atom in a Kerr medium

We investigate the emission spectra of a Ξ-type three-level atom interacting with a single-mode optical field in an ideal cavity filled with a Kerr medium and discuss the structure of emission spectrum when the optical field is initially in a pure number state and a coherent state, respectively. It is shown that the structure of emission spectrum depends not only on the photon number distribution, but also on the strength of incident field and the coupling of Kerr medium to the field.     

Dissipative optical flow in a nonlinear Fabry-Pérot cavity

We describe a classical nonlinear optical system that displays superfluidity and its breakdown. The system consists of a self-defocusing refractive medium inside a Fabry-Pérot cavity with a cylindrical obstacle. We have numerically solved for the transmitted beam when an incident plane wave strikes the cavity at an oblique angle. The presence of the incident beam pins the steady-state phase of the output, preventing the formation of vortices or time-dependent flow. When the incident beam is switched off, a transient wake of moving optical vortices is produced. This is analogous to the breakdown of superfluidity above a critical velocity.