波导自由电子激光振荡器的三维数值模拟

 建立了带波导的自由电子激光振荡器方程组，能够描述光场衍射、孔耦合输出以及电子运动、腔镜倾斜等三维问题。采用整体数值（INEX）模拟方法，研究了中国工程物理研究院（CAEP）远红外自由电子激光装置的三维问题与横模结构。结果表明：激光器的横模品质好，孔耦合输出方式下仍然是基模为主，在腔功率中所占份额约87%。研究了电子束偏入射、斜入射、腔镜倾斜等不同轴（misalignment）因素对激光器的增益、功率、输出、横模结构等的影响，并给出了最大允许值。     

Simulation of a Single-Mode Tunnel-Junction-Based Long-Wavelength VCSEL

We investigate the physics of an internal device for a high-performance, vertical-cavity surface-emitting laser operating at 1.305 μm. Experimental results are analyzed using as the simulation software a photonic-integrated-circuit simulator in 3D (PICS3D), which is a state-of-the-art 3D simulator for surface- and edge-emitting laser diodes, semiconductor optical amplifiers, and other similar active waveguide devices. The 2D/3D semiconductor equations are coupled to the optical modes in both lateral and longitudinal directions. Optical properties such as the quantum well/wire/dot optical gain and spontaneous emission rates are computed self-consistently. Careful adjustments of material parameters led to an excellent agreement between simulation and measurements. Simulation results show that the maximum output power is limited by electron leakage from quantum wells.     

(2+1)维光学孤子在饱和非线性介质中的模式特征

从非线性Schrdinger方程出发,应用数学解析的方法,详细讨论了在饱和非线性介质中(2+1)维空间光学孤子存在满足物理意义的自洽解的条件,给出数值计算所需要的边界条件。通过数值计算,给出了基模和一阶模在某一组参数下的部分模式的光场慢变包络、光强度的二维和三维分布的直观图形,以及相应能量(无量纲)。结果表明,孤子的存在不是任意的,而是依赖于一定的能量。当光脉冲能量不足以支持孤子的存在时,其解呈振荡形式,说明不存在孤子解。同时还给出介质的饱和参数、孤子在传播方向上的波矢k对孤子模式的影响等有意义的结论。     

Wavelength tuning characteristics of a fabry-perot semiconductor laser with an external short cavity

Wavelength tuning characteristics of a Fabry-Perot semiconductor laser with an external short cavity are analyzed, in which the oscillation wavelength can be changed by slightly altering the external cavity length. Analysis is based on rate equations for an optical power and carrier density. It is shown that the wavelength tuning range is dominated by a change of carrier density through the effect of carrier-induced refractive index change in the active layer of a laser diode. This depends on effective coupling coefficients of the optical field iteratively reflected back to the laser diode by the external mirror, and on reflection coefficients of an anti-reflection coated laser facet and the external mirror which compose the external cavity. The effective coupling coefficient is also derived using the waveguide theory and Kirchhoff ’s theory. Finally, an unstable condition which may limit a stable wavelength tuning range is shown by results of a linear stability analysis of rate equations.     

数值模拟辐射驱动2维内爆压缩过程

采用2维三温非平衡辐射流体力学程序LARED-H数值模拟辐射驱动内爆过程。针对2维三温能量方程九点差分格式离散后的线性方程组,采用了高效的Krysolv子空间迭代解法,改进了代数解法器。将1维间接驱动内爆总体程序CFJ与LARED-H程序的计算结果进行比对,验证了LARED-H程序数值模拟1维内爆问题的正确性。并数值模拟了不同腔长辐射温度源驱动下的2维靶球运动,数值结果显示：随着腔长的增加,高压缩内爆燃料区分别被压缩成香肠形、球形和铁饼形,数值模拟结果与神光Ⅱ的实验结果定性上相同。     

Third-harmonic generation in focused beams as a method of 3D microscopy of a laser-produced plasma

Analysis of the phase-matching integral for third-harmonic generation in focused laser beams shows that this process can be used as a method of 3D microscopy, allowing one to characterize the location and magnitude of inhomogeneities of linear and nonlinear optical characteristics of a medium. The potentialities of this method are illustrated by the results of experiments on 3D microscopy of an optical breakdown plasma.     

Effective dynamic properties of 3D composite materials containing rigid penny-shaped inclusions

The propagation of time-harmonic plane elastic waves in infinite elastic composite materials consisting of linear elastic matrix and rigid penny-shaped inclusions is investigated in this paper. The inclusions are allowed to translate and rotate in the matrix. First, the three-dimensional (3D) wave scattering problem by a single inclusion is reduced to a system of boundary integral equations for the stress jumps across the inclusion surfaces. A boundary element method (BEM) is developed for solving the boundary integral equations numerically. Far-field scattering amplitudes and complex wavenumbers are computed by using the stress jumps. Then the solution of the single scattering problem is applied to estimate the effective dynamic parameters of the composite materials containing randomly distributed inclusions of dilute concentration. Numerical results for the attenuation coefficient and the effective velocity of longitudinal and transverse waves in infinite elastic composites containing parallel and randomly oriented rigid penny-shaped inclusions of equal size and equal mass are presented and discussed. The effects of the wave frequency, the inclusion mass, the inclusion density, and the inclusion orientation or the direction of the wave incidence on the attenuation coefficient and the effective wave velocities are analysed. The results presented in this paper are compared with the available analytical results in the low-frequency range.     

Impurity-related optical response in a 2D and 3D quantum dot with Gaussian confinement under intense laser field

ABSTRACT

Using the two-dimensional (2D) diagonalisation method, the impurity-related electronic states and optical response in a 2D quantum dot with Gaussian confinement potential under nonresonant intense laser field are investigated. The effects of a hydrogenic impurity on the energy spectrum and binding energy of the electron and also intersubband optical absorption are calculated. The obtained numerical results show that the degeneracies of the excited electron states are broken and the absorption spectrum exhibits a redshift with the values of the laser field. The findings indicate a new degree of freedom to tune the performance of novel optoelectronic devices, based on the quantum dots and to control their specific properties by means of intense laser field and hydrogenic donor impurity. Using the same Gaussian confinement model, the electronic properties of a confined electron in the region of a spherical quantum dot are studied under the combined effects of on-centre donor impurity and a linearly polarised intense laser radiation. The three-dimensional problem is used to theoretically model, with very good agreement, some experimental findings reported in the literature related to the photoluminescence peak energy transition.     

Sensitivity improvement of broadband electro-optic polymer-based optical phase modulator using 1D and 2D photonic crystal structures

This Letter introduces the design and simulation of a microstrip-line-based electro-optic(EO) polymer optical phase modulator(PM) that is further enhanced by the addition of photonic crystal(PhC) structures that are in close proximity to the optical core. The slow-wave PhC structure is designed for two different material configurations and placed in the modulator as a superstrate to the optical core; simulation results are depicted for both1 D and 2D PhC structures. The PM characteristics are modeled using a combination of the finite element method and the optical beam propagation method in both the RF and optical domains, respectively.The phase-shift simulation results show a factor of 1.7 increase in an effective EO coefficient(120 pm/V) while maintaining a broadband bandwidth of 40 GHz.     

激光线聚焦驱动平面银靶的二维数值模拟

介绍新研制的二维非平衡辐射流体力学程序XRL2D的物理方程以及计算方法,并对神光Ⅱ上典型的类镍银X光激光实验条件,用3种ALE计算方法模拟了预主脉冲线聚焦驱动银平面靶的流体运动.几种方法模拟给出的物理图像清晰且相似,类镍离子丰度分布呈弯月形,同实验上XRL场图呈弯月形分布一致.对3种计算方法给出的结果进行了细致的比较分析.     

3D raman sideband cooling of cesium atoms at high density

We laser cool 5x10(7) Cs atoms to a spin-polarized phase space density of 1/30, the highest ever obtained by laser cooling. It is achieved by compression and polarization gradient cooling in a 3D far-off-resonant optical lattice, followed by 3D Raman sideband cooling optimized at a density of 1.5x10(12) atoms/cm(3), and adiabatic release. In the lattice, 23% of the sites are occupied, 95% of the atoms are in the lowest energy magnetic sublevel, and 37% are in the lowest 3D vibrational state.     

线结构激光-机器视觉三角测量光路设计

给出了线结构激光 -机器视觉三角测量的通用光路计算公式。公式考虑了激光入射角、CCD面阵与光轴的各种变化情况 ,对激光机器视觉测量系统的光路结构设计有一定的指导意义。     

Bose-Einstein condensates in 1D optical lattices

We discuss the Bloch-state solutions of the stationary Gross-Pitaevskii equation and of the Bogoliubov equations for a Bose-Einstein condensate in the presence of a one-dimensional optical lattice. The results for the compressibility, effective mass and velocity of sound are analysed as a function of the lattice depth and of the strength of the two-body interaction. The band structure of the spectrum of elementary excitations is compared with the one exhibited by the stationary solutions (Bloch bands). Moreover, the numerical calculations are compared with the analytic predictions of the tight binding approximation. We also discuss the role of quantum fluctuations and show that the condensate exhibits 3D, 2D or 1D features depending on the lattice depth and on the number of particles occupying each potential well. We finally show how, using a local density approximation, our results can be applied to study the behaviour of the gas in the presence of harmonic trapping.Received: 15 July 2003, Published online: 8 October 2003PACS: 03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow - 03.75.Lm Tunneling, Josephson effect, Bose-Einstein condensates in periodic potentials, solitons, vortices and topological excitations     

波导自由电子激光振荡器的三维数值模拟

建立了带波导的自由电子激光振荡器方程组,能够描述光场衍射、孔耦合输出以及电子运动、腔镜倾斜等三维问题。采用整体数值（INEX）模拟方法,研究了中国工程物理研究院（CAEP）远红外自由电子激光装置的三维问题与横模结构。结果表明：激光器的横模品质好,孔耦合输出方式下仍然是基模为主,在腔功率中所占份额约87%。研究了电子束偏入射、斜入射、腔镜倾斜等不同轴（misalignment）因素对激光器的增益、功率、输出、横模结构等的影响,并给出了最大允许值。     

等离子体波背景下的光子Berry相位

利用光学度规将强激光脉冲激发的电子等离子体波描述为有效几何背景.借助于广义相对论中弯曲时空下的Maxwell方程组得到了探针光子在等离子体中电子等离子体波背景下(被处理为有效度规)所满足的运动方程及光子的Hamilton表达式.导出了电子等离子体波对光子Berry相位贡献的解析表达式并且对光子在真空中Berry相位的修正做了数值估算. 关键词： 电子等离子体波 等离子体 Berry相位     

Theory of carrier gain dynamics in InGaAs/AlGaAs strained-layer single-quantum-well diode lasers

Calculations of the femtosecond gain dynamics in InGaAs/AlGaAs strained-layer single-quantum-well diode lasers are presented and compared to experiments which use a novel multiple-wavelength pump probe technique. We develop a detailed theoretical model for the gain dynamics in a quantum well laser diode structure to aid in the interpretation of gain dynamics induced by both interband absorption and stimulated emission of photons. In the model, transient gain and differential transmission are computed in a multiband effective mass model including biaxial strain, valence subband mixing, and scattering both within and between subbands. The transient photogeneration of electron-hole pairs by the pump pulse and subsequent relaxation of carriers by both polar optical phonon scattering and carrier-carrier scattering are calculated within a Boltzmann equation framework. A relaxation approximation for the carrier-carrier scattering is made making the coupled Boltzmann equations an effective one dimensional model which are then solved using an adaptive Runge-Kutta technique rather than a more computationally intensive Monte Carlo approach.     

Bound states and Cooper pairs of molecules in 2D optical lattices bilayer

We investigate the formation of Cooper pairs, bound dimers and the dimer‐dimer elastic scattering of ultracold dipolar Fermi molecules confined in a 2D optical lattice bilayer configuration. While the energy and their associated bound states are determined in a variational way, the correlated two‐molecule pair is addressed as in the original Cooper formulation. We demonstrate that the 2D lattice confinement favors the formation of zero center mass momentum bound states. Regarding the Cooper pairs binding energy, this depends on the molecule populations in each layer. Maximum binding energies occur for non‐zero (zero) pair momentum when the Fermi system is polarized (unpolarized). We find an analytic expression for the dimer‐dimer effective interaction in the deep BEC regime. The present analysis represents a route for addressing the BCS‐BEC crossover in dipolar Fermi gases confined in 2D optical lattices within the current experimental panorama.     

The effects of hydrostatic pressure and intense laser field on the linear and nonlinear optical properties of a square quantum well

In this paper, the effects of hydrostatic pressure, temperature and intense laser field on the linear and nonlinear optical processes in the conduction band of a square quantum well are numerically investigated in the effective mass approximation. The analytical expressions of optical properties are obtained by using the compact density-matrix approach. The numerical results are presented for typical square GaAs/Al_xGa_1?xAs single quantum well system. The nonlinear optical absorption and refractive index changes depending on the hydrostatic pressure and intense laser field are investigated for two different temperature values. The results show that the intense laser field, the hydrostatic pressure and the temperature have a significant effect on the optical characteristics of these structures.     

Angle extended linear MEMS scanning system for 3D laser vision sensor

Scanning system is often considered as the most important part for 3D laser vision sensor. In this paper, we propose a method for the optical system design of angle extended linear MEMS scanning system, which has features of huge scanning degree, small beam divergence angle and small spot size for 3D laser vision sensor. The principle of design and theoretical formulas are derived strictly. With the help of software ZEMAX, a linear scanning optical system based on MEMS has been designed. Results show that the designed system can extend scanning angle from ±8° to ±26.5° with a divergence angle small than 3.5 mr, and the spot size is reduced for 4.545 times.     

Generating a quasiellipsoidal electron beam by 3D laser-pulse shaping

A generic 3D laser-pulse-shaping scheme is proposed towards the generation of a uniform ellipsoidal particle distribution, an ideal distribution due to the linear dependence of the space-charge force on the particle position. The shaping is accomplished via spatiotemporal coupling of the laser dynamics via chromatic aberration in an optical lens. Particle tracking simulations show that the electron beam initiated by such a laser pulse in a high-gradient radio-frequency photoinjector delivers very low emittance, ideal for beam-based light sources such as the x-ray free-electron laser.