双模纠缠相干光与Bell态原子系统的光子统计

运用全量子理论并结合数值计算方法,研究了处于Bell态的两个全同二能级纠缠原子与双模纠缠相干光场相互作用系统的光子统计性质.分析了双原子体系的初态、光场的平均光子数、双模纠缠相干光场的纠缠程度以及双原子体系的原子间耦合强度对双模光场的光子统计性质的影响.结果表明：双原子体系的初态为｜β00〉、｜β10〉时,光场在其演化过程中不出现光子的反聚束效应;而当原子初态为｜β01〉或｜β11〉时,在一定的条件下可出现光子的反聚束效应.并且在光场的演化过程中,光子的反聚束效应出现的次数、时间和深度极其敏感地依赖于初始光场的平均光子数,而受到双模纠缠光场的纠缠程度以及双原子间偶极作用强度的影响很微弱.     

Optical nonlinearity measurement of 4-（N-methyl,N-hydroxyethl）amino,4＇-nitroazobenzene using a transmittance technique with a phase object（T-PO） with top-hat beams at 600-nm wavelength

The transmittance technique with a phase object（T-PO）,for measuring optical nonlinear coefficients is proposed with a top-hat beam.The sensitivity of the T-PO with a top-hat beam is a factor of 4 greater than that with a Gaussian beam.The validity of this method is verified by measuring the nonlinearity of a well-characterized liquid,CS 2 at 532-nm wavelength.The ease of use of this method has been proved by measuring a new compound 4-（N-methyl,N-hydroxyethyl）amino,4＇-nitroazobenzene（ANAB） at 600-nm wavelength,indicating that this method can be extended to the measurement of optical nonlinearities in a wide-band spectrum.     

An asymptotic solving method for the periodic solution of a class of disturbed nonlinear evolution equation

<正>A class of disturbed evolution equation is considered using a simple and valid technique.We first introduce the periodic traveling-wave solution of a corresponding typical evolution equation.Then the approximate solution for an original disturbed evolution equation is obtained using the asymptotic method.We point out that the series of approximate solution is convergent and the accuracy of the asymptotic solution is studied using the fixed point theorem for the functional analysis.     

二维复式声子晶体中基元配置对声学能带结构的影响

研究了二维复式声子晶体中基元配置对其声学能带结构的影响,发现当声子晶体的基元配置改变时,声子晶体的不可约布里渊区也会改变,而且部分能带的极值不再在高对称线上.特别地,在某些基元配置下,不可约布里渊区扩大为整个第一布里渊区.因此,对于对称性较高的复式晶格声子晶体,可用通常的方法得到能带结构,而对于对称性较低的复式晶格结构声子晶体,只有采用对整个第一布里渊区进行研究的方法,才能获得可信的能带结构及带隙.     

Friction phenomena in a two-dimensional Frenkel-Kontorova model

By using the molecular dynamic simulation method with a fourth-order Runge--Kutta algorithm, a two-dimensional dc- and ac-driven Frenkel--Kontorova (FK) model with a square symmetry substrate potential for a square lattice layer has been investigated in this paper. For this system, the effects of many different parameters on the average velocity and the static friction force have been studied. It is found that not only the amplitude and frequency of ac-driven force, but also the direction of the external driving force and the misfit angle between two layers have some strong influences on the static friction force. It can be concluded that the superlubricity phenomenon appears easily with a larger ac amplitude and lower ac frequency for some special direction of the external force and misfit angle.     

Frenkel-Kontorova模型中垫底势对最大静摩擦力的影响

用一维Frenkel-Kontorova模型,对相互接触的两个单原子分子链具有相对运动趋势时所产生的最大静摩擦力进行了研究.分别在相邻原子的距离与周期势场的周期比b/a为可公度(commensurate)、黄金分割(golden mean)、螺旋分割(spiral mean)三种情况下,描述了特殊垫底势力的振幅A与分子链静摩擦力的关系,在特殊垫底势力的作用下上层原子链弹性系数K对静摩擦力的影响.研究表明,垫底势力的形式对静摩擦力的大小有很重要的影响. 关键词： Frenkel-Kontorova模型 静摩擦力     

Planar waveguides in neodymium-doped calcium niobium gallium garnet crystals produced by proton implantation

In this work, the fabrication and optical properties of a planar waveguide in a neodymium-doped calcium niobium gallium garnet(Nd:CNGG) crystal are reported. The waveguide is produced by proton(H~+) implantation at 480 ke V and a fluence of 1.0×10~(17) ions/cm~2. The prism-coupling measurement is performed to obtain the dark mode of the waveguide at a wavelength of 632.8nm. The reflectivity calculation method(RCM) is used to reconstruct the refractive index profile. The finite-difference beam propagation method(FD-BPM) is employed to calculate the guided mode profile of the waveguide.The stopping and range of ions in matter 2010(SRIM 2010) code is used to simulate the damage profile induced by the ion implantation. The experimental and theoretical results indicate that the waveguide can confine the light propagation.     

带陡化间隙的触发真空开关触发源研制北大核心CSCD

针对主电极间距20mm以上的沿面击穿型多棒极触发真空开关(TVS),研制了开关触发源。触发源利用脉冲变压器产生脉冲高压输出,在脉冲变压器高压侧并联小容值电容并在电容后串联陡化间隙。陡化间隙的加入可以使触发源输出不受触发沿面金属蒸气沉积的影响。通过调节间隙击穿电压也可以提高电容充电电压及储存能量,从而增加TVS触发沿面被击穿时注入到其中的触发能量。使用该触发源对TVS进行导通实验,结果表明,加入陡化间隙后的触发源输出能量大幅提高且不受触发沿面金属蒸气沉积的影响,能够实现TVS的100%可靠导通。     

纳秒级脉冲激光自动跟踪积分式测量方法

介绍了一种纳秒级脉冲激光光斑能量分布测量电路的设计方法,采用自动跟踪积分方式,根据预测先将脉冲光电流积分并保存,然后用速度较低的A/D芯片进行A/D转换,该方法避免了采用高速A/D芯片,且可以获得较高的采样分辨率,特别是在需要采集的通道数较多时具有明显优势。     

海洋湍流中光波特征参量和短期光束扩展的研究

Nikishov等建立的海洋湍流功率谱模型中,假设了海水有着稳定的分层.但是,实际海水通常不是稳定分层的,温度与盐度的涡流扩散率是不相等的.2017年,Elamassie等建立了考虑这些因素的更合理的海洋湍流功率谱模型.湍流介质中光波空间相干长度等基本特征参量在表征湍流强度和光传输相位校正技术等方面起着重要作用.本文基于Elamassie海洋湍流功率谱模型,重新推导出了海洋湍流中光波结构函数、光波空间相干长度和Fried参数的解析公式,并校验了所得公式的正确性.研究发现：当温度变化引起的光学湍流占主导地位时,Nikishov海洋湍流功率谱模型把湍流强度低估了;当盐度变化引起的光学湍流占主导地位时,Nikishov海洋湍流功率谱模型把湍流强度高估了.基于Elamassie海洋湍流功率谱模型,本文推导出了高斯光束短期光束扩展的半解析公式,并验证了其正确性.研究还表明：海水稳定分层与否,短期光束扩展差异很大.本文研究结果对水下湍流环境中的光通信、成像和传感等应用具有重要意义.