Enhanced gain and narrow linewidth of an optical cavity by the Doppler effect in a four-level atomic system

Abstract

A scheme for high gain and narrow linewidth of an optical cavity with a four-level atomic system is proposed by the Doppler effect via active Raman gain (ARG) process. Atomic motion leads to Doppler frequency shift which induces constructive interference for the linear susceptibility. The enhanced normal dispersion greatly narrows the cavity linewidth, and the amplified gain gives rise to a high cavity transmission. Simulation results show that the cavity linewidth based on ARG is about one order of magnitude narrower than that based on electromagnetically-induced transparency under the same conditions, and the cavity transmission intensity could be enhanced by nearly 30 times.     

Fano resonances of a metal nanorod array with a symmetry breaking wedge and gain medium filling

Fano resonances of a metal nanorod array with a symmetry breaking wedge and gain medium filling have been explored using the finite-difference time-domain method. Results show that a periodic symmetry breaking nanorod array supports Fano resonance due to the interaction between a hybridized dipolar plasmon mode of the nanorod and a narrower quadrupolar mode of the slice. By a tiny increase of the imaginary part of the dielectric constant of the gain medium, the Ohmic loss can be counteracted, and Fano resonance dip gets deeper significantly. Additionally, the modulation depth can be improved by changing the real part of the gain medium dielectric constant. The results found are useful for further develop of the devices on the basis of the Fano resonance and its modulation.     

Tunneling-induced high gain and narrow linewidth of a cavity with an asymmetric quantum-well system

A scheme is proposed for obtaining high gain and narrow linewidth of a cavity with an asymmetric quantum-well system. Due to resonant tunneling, destructive interference for linear absorption leads to a tunneling-induced transparency window which compresses the cavity linewidth; moreover, constructive interference for cross-nonlinear susceptibility occurs, which introduces high gain and large dispersion, and the cavity linewidth is much compressed. In the latter case, the intensity of cavity transmission could be enhanced one order of magnitude larger than that of input field, and its linewidth could be one-seventieth of the empty cavity.     

A mixed integer programming model for a closed-loop supply-chain network

In this paper, a new mixed integer mathematical model for a closed-loop supply-chain network that includes both forward and reverse flows with multi-periods and multi-parts is proposed. The proposed model guarantees the optimal values of transportation amounts of manufactured and disassembled products in a closed-loop supply chain while determining the location of plants and retailers. Finally, computational results are presented for a number of scenarios to show and validate the applicability of the model.     

昆明地区直接受益式太阳房室内温度研究

为了直观了解昆明地区太阳房的室内温度分布情况,本文以昆明地区2012年11月实测气象数据为研究依据,利用太阳房热平衡计算辅助流体分析及仿真软件FLUENT计算和模拟出昆明地区直接受益式太阳房室内温度及温度场分布,得出室内温度分布不均可以通过改变南面窗墙比来改善的结论.     

提高弱电网中光伏并网逆变器稳定性的控制方法

随着电网中分布电源的增加,电网呈现出了弱电网特性。电网阻抗使得逆变器与电网之间存在相互作用,对逆变器的稳定性产生影响,威胁着系统的安全稳定运行。从相位角度分析了电网阻抗对系统稳定性的影响,电网阻抗的增加会导致系统相位降低,继而使系统进入不稳定状态。为增强系统在电网阻抗变化过程中的鲁棒性,提出一种基于神经网络的逆变器变增益控制方法。该方法采用一定的控制环节补偿系统相位,采用径向基函数神经网络建模的方法实时调整系统的开环截止频率,使相位裕度始终保持最大值。仿真结果验证了本文的理论分析。     

光纤光栅中心波长与设计波长偏移量对外腔LD的影响

本文在三腔镜模型近似的情况下,利用等效腔模型,完成了光纤光栅外腔半导体激光器（FBG-ECL）的理论建模。利用光纤布拉格光栅（fiber Bragg grating）相关理论,对FBG-ECL模型进行了修正,着重考虑了光纤Bragg光栅的折射率分布、中心波长偏移以及边模抑制比对FBG-ECL性能的影响。对FBG-ECL的等效反射率、阈值增益和线宽特性进行了数值分析。结果表明,在考虑光纤Bragg光栅中心波长与设计波长偏移量、光栅反射率分布以及边模抑制比后,等效腔理论模型更加符合实际情况,使得可以更加符合实际情况地分析光纤光栅外腔半导体激光器相关特性,并且对设计应用于FBG-ECL的光纤光栅有一定的指导意义。     

大功率五坐标机床A轴的新型控制算法设计

针对齿隙和非线性摩擦对A轴控制精度的影响,设计了增益自调节模糊控制器,通过引入基于连续指数函数的增益自调节策略,消除了传统模糊控制中增益切换引起的控制律突变.虽然增益自调节模糊控制可以实现良好的动态响应和较小的稳态误差,但其需要二维模糊控制规则表来计算控制律,这在一定程度上影响了控制系统的动态响应速度.因此,设计了增益自调节模糊滑模控制器,通过采用模糊控制来逼近滑模等效控制律中的非线性函数项,消除了传统滑模控制的抖振现象.实验结果表明,本文所设计的两种控制算法均能实现较快的零超调动态响应及较高的稳态精度,能有效提高整体叶盘型面的加工精度和表面一致性,并显著降低叶片表面粗糙度.     

Beam Driven Tokamak Fusion Reactors

The recent successes in neutral beam current drive experiments on large tokamaks prompt us to consider the prospect of a beam driven steady state tokamak fusion reactor. A neo-classical theory on the beam driven current, which fully includes the toroidal effects on the induced ion and electron currents and is the most reliable to date, is reviewed in this article. The prospect of steady state tokamaks predicted by the theory may be somewhat pessimistic if the plasma current is sustained only by the beam driven current, because too much beam power is necessary for the current drive. However, thanks to the bootstrap current which was discovered in many tokamaks in recent years, the feasibility of a continuous tokamak operation will probably be highly improved because several tens of percent of the current will be produced by the bootstrap current. The energy gain Q would attain 30 to 50 in the power reactor and about 10 even for next generation (demonstration size) tokamaks.     

Calcuiational Method for Neutron Heating in Dense Plasma Systems, (II)

Abstract

The effect of neutron heating on the burn characteristics of inertial confinement fusion pellets is investigated by applying the calcuiational method developed in an earlier paper (Part I). The basic equations are time-dependent transport equations for fusion neutrons and recoil ions, being written in terms of the modified Eulerian coordinates originally proposed by Wienke (1974). After incorporating these equations into the one-dimensional hydrodynamics code MEDUSA, burn simulations are made for isobaric D-T pellets models compressed to 1,000 times the liquid density. It is found that in reactor-grade pellets, the inclusion of neutron heating decreases the fuel gain from the values obtained by neglecting the neutron heating. Calculations neglecting the energy transport by recoil ions overestimate the neutron energy deposition to plasma ions. The energy spectrum of neutrons emitted out of a typical D-T burning pellet is also shown. These neutrons contain fast components whose energies reach more than 20MeV.