Atomic dynamics in the mode－mode competition system

The atomic dynamical properties in the system with competing k-photon and l-photon transitions are studied fully by means of quantum theory. We discuss the influences of the mode－mode competition, the relative competing strengths of the atom and the two-mode field, and the initial state of the system on the atomic dynamics. We show that the presence of the mode－mode competition can result in quite a periodical collapses-revivals of the atomic inversion and the increase of the initial photons of the system can lead to the collapse－revival phenomenon and prolong the revival time of the atomic inversion.     

Denisov-type quasi-optical mode converter forhigher-order asymmetric volume mode gyrotron北大核心CSCD

The principle and design method of Denisov-type quasi-optical mode converter is investigated indetail. The operation process of the Denisov-type launcher is analyzed by applying the geometrical optics, andthe Gaussian-like field distribution achieved on the waveguide wall is also derived. The method for designing arippled-wall launcher is proposed on the basis of coupled mode theory. A simulation code for Denisov-type qua-si-optical mode converter GQOMC-D is developed based on coupled mode theory, vector diffraction integrationand physical optics, which is compared to the design parameters and experimental results reported in literaturefor its validity. According to this code, a Denisov-type quasi-optical mode converter used in 110 GHz TE22.6mode gyrotron oscillators is designed. Simulation results indicate that a Gaussian-like beam is obtained at theoutput window with a scalar content of 98.4 % and a conversion efficiency of 94.7 %.     

Inversion of acoustic mode coupling coefficient matrix

It is found that the normal mode amplitude time series consist of multi-frequency component by analyzing the structure of acoustical signal when internal wave propagation exists, and each frequency is the product of internal wave speed and the normal mode wave number difference between acoustical receivers and source. The amplitude of each component is proportional to the acoustic mode coupling coefficient. The structure of the normal mode coefficient time series is still complex even the internal waves do not reshape when they propagate from the acoustical receivers to the source. A method is presented to compute the AMCCM by the feature of IWs' motion and the relation between the AMCCM and the acoustical signal fluctuation amplitude. The IWs data measured in the 2001 Asia experiment (ASIAEX2001) is used to check the accuracy of this method by numerical simulation. It is show that the method is accurate to compute the AMCCM.     

Effect of mode mode-competition on atom-atom entanglement

A system consisting of two atoms interacting with a two-mode vacuum is considered, where each atom is resonant with the two cavity modes through two different competing transitions. The effect of mode--mode competition on the atom--atom entanglement is investigated. We find that the entanglement between the two atoms can be induced by the mode--mode competition. For the initial atomic state |\varPsi(0)\rangle, whether the atoms are initially separated or entangled, a large or even maximal entanglement between them can be obtained periodically by introducing the mode--mode competition. For the initial atomic state |\varPhi(0)\rangle, the strong mode--mode competition can prevent the two atoms entangled initially from suffering entanglement sudden death; besides, it makes them in a more stable and longer-lived entanglement than in the non-competition case.     

Research on algorithms for ultrasonic reflection mode tomography

In this paper,mathematical analysis shows that the reconstruction ofultrasonic reflection mode tomography using a single transducer acting as bothsource and receiver far from the object can be obtained by employingfiltered-backprojection algorithm which is widely used in X-ray tomography;but when the transducer is near to the object,this algorithm will result in imagedistortion.On the basis of mathematical analysis,we propose a new algorithm.Computer simulation demonstrates an obvious improvement in the reconstruct-ed images employing this algorithm over the conventionalfiltered-backprojection method of X-ray tomography.     

New amplitude equation of single—mode laser

The white-gain model and the white-loss model of a single-mode laser are investigated in the presence of cross-correlations between the real and imaginary parts of quantum noise as well as pump noise. It was found that, like the white cubic model (2001 Chin. Phys. Lett. 18 370), the amplitude equations are all decoupled from the phase equations for the two models, and the same novel term appears in the amplitude equations of the two models. So we can put the amplitude equations of all the models into a general form, that is, the new amplitude equation. We further use this new amplitude equation to study specifically the stationary properties of the laser intensity for the white-gain model.     

Behavior of single mode optic-fiber ring resonant hydrophone

1IlltroductionSevera.linvestigatorshavestudiedthiskindofopticalfiberinterferometrichydrophone.InterferometricconfigurationsusedforacousticdetectionaretheMadsZehnder,theFabryPerotandthemng-resonator.TheMach-Zehaderconsistsoftwoopticfibers,oneusedassigfialarm)theotherforanacousticallydesensitizedreferencea-rm,andthatleadstocomplexunderwaterdesign.Thesingle-cavityFbary-PerotisthesimplestconfigUIation,butitshighbackreflectancetowardthelasertendstodestabilizedthesource,thuSitrequiressomeisolat…     

Test of BESⅢ RPC in the avalanche mode

The installation of the BESⅢ RPC system has been completed. Cosmic ray test results show that they perform very well in streamer mode and meet the BESⅢ requirements. We have tested several RPCs in the avalanche mode with the addition of extra SF₆ in the gas mixture. We find an efficiency plateau that reaches ～95%, and a time resolution of 1.8 ns. This demonstrates that the BESⅢ-type RPC can work in the avalanche mode as well.     

Compact first and second order polarization mode dispersion emulator

Polarization mode dispersion (PMD) is becoming major system impairment in high speed and long distance opti- cal fiber transmission systems. Since the PMD-induced pulse spreading is a frequency-dependent statistic pa- rameter and varies randomly over time, it is difficult to be compensated[1-3]. Large length of single mode opti- cal fiber is needed to generate certain amount of PMD in laboratory, and the PMD effect in the fiber varies slightly and slowly over time. Therefore, PMD emula- …     

Guiding mode in elliptical core microstructured polymer optical fiber

A kind of microstructured polymer optical fiber with elliptical core has been fabricated by adopting in- situ chemical polymerization technology and the secondary sleeving draw-stretching technique.Microscope photography demonstrates the clear hole-structure retained in the fiber.Though the holes distortion is visible,initial laser experiment indicates that light can be strongly confined in the elliptical core region, and the mode field is split obviously and presents the multi-mode characteristic.Numerical modeling is carried out for the real fiber with the measured parameters,including the external diameter of 150μm,the average holes diameter of 3.3μm,and the average hole spacing of 6.3μm by using full-vector plane wave method.The guided mode fields of the numerical simulation are consistent with the experiment result. This fiber shows the strong multi-mode and weak birefringence in the visible and near-infrared band,and has possibility for achieving the fiber mode convertors,mode selective couplers and so on.     

Normal mode propagation of impulsive soundwith moving source and receiver

A representation of impulsive sound propagation with a moving source and receiver in an ocean waveguide is derived based on the normal mode theory. The Doppler shift of individual normal mode of narrow-band pulse is analyzed. A Doppler matched condition and Doppler compensation intervals are obtained based on the analysis of the correlation between the emitted and received signals. An experiment of long-range impulse propagation at 55km in a shallow water is used to verify the theoretical results of the Doppler shift compensation.     

Compact all-optical switches based on photon-induced suppression of mode interference

An optically activated optical switch based on suppression of mode interference (SMI) is presented. The imaging properties of multi-mode interference (MMI) section in the switch with Y-branch can be modified by a controlling light injection. The switch was simulated by finite difference beam propagation method (FD-BPM) and fabricated on GaAlAs/GaAs epitaxial materials. At the wavelength of 1.31 μm, the primary experiment showed an extinction ratio of about 8 dB with controlling light power density of 73.5 W/mm2.     

The WKBZ mode approach to pulsed propagation in ocean channels

In the paper, the WKBZ normal mode approach has been applied to the propagation of the pulsed energy and waveform in ocean channels. The numerical results in two different channels are given. Comparison between the WKBZ and conventional normal mode codes shows that the WKBZ mode approach is a fast and accurate method and the running time by the WKBZ approach is reduced by about two orders of magnitude.     

Simulation of radio-frequency atmospheric pressure glow discharge in γ mode

The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.     

Error detection using mode information of macroblocks for video transmission

When video signals are transmitted over noisy chan-nels such as wireless networks, there will be errors inthe transmitted bit stream. Traditional coding methodsmake video more sensitive to channel errors because ofspatial and temporal propagation due to using variablelength codes (VLC) and motion compensation, respec-tively. Error detection and concealment are extremelyimportant components of error robust video codec. Theprocess of error detection can be divided into two steps.First, video b…     

A theory of the weakly pinned Fröhlich mode

Extending earlier work of Littlewood (1987) a theory for the collective mode (Fröhlich mode) response of weakly pinned charge density waves (CDW) is given. Long range Coulomb interaction is incorporated in both a proper definition of the measured ac conductivity _CDW() and in the Fukuyama-Lee-Rice treatment of phason dynamics. The frequency and wave number dependent quasi particle resistivity is shown to appear only in the internal phason lines in the perturbation expansion of the impurity averaged phason propagatorD _ren. Quantitative results for _CDW() are evaluated within the self-consistent Born approximation toD _ren in three spatial dimensions taking anisotropy into account. Besides the low frequency relaxation mode we find a significant effect of the longitudinal optical phason _LO on the Fröhlich mode pinning frequency when descreening sets in at low temperatures. This is yet another manifestation of selection rule breaking by inhomogeneous pinning and establishes the special role that _LO plays in the dynamics of CDW. An explicit analytical formula for _CDW() is given and discussed in some detail including the important analyticity properties. Available measurements of the linear ac response in a wide range of frequencies and conductivities are compared with the theory and found to agree with the theoretical predictions supporting the concept of weak pinning in CDW.     

Filter control polarization mode dispersion in dispersion managed soliton systems

In this paper, the dispersion managed soliton (DMS) transmission equation is built on considering the effects of polarization mode dispersion (PMD) and filter control. The DMS transmission of filtering control in constant birefringence fibers is firstly analyzed by varitional method, from which the evolving rules of characteristical DMS parameters are obtained. Secondly, the stability of DMS transmission and its timing jitter are investigated in the random varying birefringence fibers with the conventional model of PMD. The results reveal that filter control DMS system has powerful robustness to PMD effects and DMS's timing jitter can be decreased considerably with the help of filters.     

10-W cladding-pumped fiber laser with single transverse mode output

A Yb-doped double-clad fiber laser is demonstrated with a measured power output of 10.6 W and a fundamental spatial mode. The optical-to-optical conversion efficiency is 44% and the slope efficiency is 86% closed to quantum efficiency of optical conversion. In our laser system, a D-shape (340 μm/400 μm) inner cladding Yb-doped fiber is used as the gain material within the Fabry-Perot cavity. Multimode diode pump radiation is injected into the cladding through an end facet of the composite fiber.