基于随机并行梯度下降算法的多波长激光相干合成

由于受到受激布里渊散射(SBS)等非线性效应的限制,单频激光放大器的功率在百瓦量级,以非单频激光多波长激光作为种子源能够有效地抑制SBS并提高放大器功率.与单频激光相干合成相比,非单频率、多波长激光的相干合成有望将输出激光功率成量级地提高.基于随机并行梯度下降(stochastic parallel gradient descent,SPGD)算法,实现了四波长激光的相干合成.在系统闭环时,四路多波长激光合成后的主瓣能量能够提高3倍,达到理想值的75%.验证了多波长、非单频激光相干合成的可行性,为高功率相干合成的发展提供了新的途径.     

基于波叠加法的近场声全息空间分辨率增强方法

提出一种基于波叠加法的近场声全息空间分辨率增强方法. 该方法在波叠加法的基础上,利用全息面声压信号求得布置在全息面附近的虚源面上的简单源源强,再根据求得的简单源源强实现对全息面声压的插值,进而利用插值后的全息面声压数据进行重建. 该方法可以提高近场声全息重建图像的空间分辨率,减少测量工作量,简化测量过程. 通过仿真对影响插值结果的参数进行了分析,给出了合理的选取范围;通过仿真和实验研究验证了该方法的有效性. 关键词： 波叠加法 近场声全息 空间分辨率     

强脉冲激光在AZ31B镁合金中诱导冲击波的实验研究

为了研究强脉冲激光在镁合金中诱导冲击波的衰减,采用Nd:Glass脉冲激光(1054 nm,23 ns)对AZ31B变形镁合金试样表面进行冲击,并利用响应快、测量范围大的PVDF压电膜传感器以及示波器实时测量了强脉冲激光在镁合金靶中诱导激光冲击波的相对压力.根据冲击波每次在靶材背面反射时,所经过距离的不同得到激光冲击波在镁合金中的衰减规律.结果表明,在激光能量为5J的强脉冲激光作用下,镁合金中冲击波衰减的平均速度为5.83×10³ m/s,与镁合金中应力波纵波的传播速度相符;强脉冲激光诱导冲击波在镁合金中是以指数规律衰减的.试验所得分析结果对激光冲击强化镁合金的应用具有重要意义. 关键词： 激光 镁合金 压电膜传感器 衰减规律     

局域椭圆偏振光束强聚焦性质的研究

数值计算了局域椭圆偏振光束强聚焦时在焦平面上的横向场强分布、纵向场强分布、横向能流以及纵向角动量分布.结果显示在焦平面上光束总的纵向角动量为零,但在不同象限光束具有不同方向的纵向角动量.当相位延迟角度在0到π之间变化时横向场强分布基本不变,但纵向场强分布有很明显的变化.液晶相位延迟器由外部电压控制,使其相位延迟角度能在0到π之间可以连续取值.因而液晶相位延迟器的外接电压可以实现对焦平面上的纵向场强以及纵向角动量的实时调控.     

基于闪锌矿晶体中受激电磁耦子散射产生可调谐太赫兹波的理论研究

基于受激电磁耦子散射原理,采用已报道的利用非线性光学参量振荡方法产生可调谐太赫兹波的实验条件作为理论分析的实验模型,以GaAs,GaP, InP,ZnTe晶体为代表,计算分析了在闪锌矿晶体中参量振荡产生太赫兹波的吸收、增益特性,对输出THz波的调谐特性给出了详尽分析.分析太赫兹波高效耦合输出的腔型结构,并与掺氧化镁铌酸锂晶体组成的太赫兹波参量振荡器做对比. 关键词： 太赫兹波 太赫兹波参量振荡 电磁耦子 闪锌矿晶体     

弹性波通过一维复合材料系统的透射性质

提出了不同结构的一维弹性波复合材料系统模型,包括一维周期结构声子晶体、标准Fibonacci准周期结构声子晶体、广义Fibonacci准周期结构声子晶体以及完全无序结构的复合材料系统. 采用模式匹配理论法,数值计算了弹性波通过一维复合材料系统的透射系数. 计算结果表明,利用特殊的准周期结构声子晶体可获得比周期结构声子晶体更宽的带隙范围,准周期结构排列的复合材料系统相当于在周期结构中引入了缺陷体一样,带隙内出现了丰富的局域模式. 对弹性波/声波在复合材料系统中局域态性质的研究有助于弹性波/声波滤波器、导波器 关键词： 弹性波复合材料 局域化     

高迁移率聚合物薄膜晶体管

以高掺杂Si单晶片作为栅电极, 热生长SiO₂作为栅介质层, 聚三己基噻吩薄膜作为半导体活性层, Au作为源、漏电极, 并采用十八烷基三氯硅烷（OTS）对栅介质表面改性, 在空气环境下成功地制备出高性能聚合物薄膜晶体管. 结果表明, 通过采用OTS对栅介质层表面修饰大幅度地改善了聚合物薄膜晶体管的电性能, 器件的场效应迁移率高达0.02 cm²/（Vs）, 开关电流比大于10⁵. 关键词： 聚合物薄膜晶体管 聚三己基噻吩 场效应迁移率 表面修饰     

Strain distributions and electronic structure of three-dimensional InAs/GaAs quantum rings

This paper presents a finite element calculation for the electronic structure and strain distribution of self-organized InAs/GaAs quantum rings. The strain distribution calculations are based on the continuum elastic theory. An ideal three-dimensional circular quantum ring model is adopted in this work. The electron and heavy-hole energy levels of the InAs/GaAs quantum rings are calculated by solving the three-dimensional effective mass Schr?dinger equation including the deformation potential and piezoelectric potential up to the second order induced by the strain. The calculated results show the importance of strain and piezoelectric effects, and these effects should be taken into consideration in analysis of the optoelectronic characteristics of strain quantum rings.     

Mǒsbauer study of the field induced uniaxial anisotropy in electro-deposited FeCo alloy films

Thin ferromagnetic films with in-plane magnetic anisotropy are promising materials for obtaining high microwave permeability.The paper reports a Mo¨ssbauer study of the field induced in-plane uniaxial anisotropy in electro-deposited FeCo alloy films.The FeCo alloy films were prepared by the electro-deposition method with and without an external magnetic field applied parallel to the film plane during deposition.Vibrating sample magnetometry and Mo¨ssbauer spectroscopy measurements at room temperature indicate that the film deposited in external field shows an in-plane uniaxial anisotropy with an easy direction coinciding with the external field direction and a hard direction perpendicular to the field direction,whereas the film deposited without external field does not show any in-plane anisotropy.Mo¨ssbauer spectra taken in three geometric arrangements show that the magnetic moments are almost constrained in the film plane for the film deposited with applied magnetic field.Also,the magnetic moments tend to align in the direction of the applied external magnetic field during deposition,indicating that the observed anisotropy should be attributed to directional ordering of atomic pairs.     

Analysis and finite element simulation of electromagnetic heating in the nitride MOCVD reactor

Electromagnetic field distribution in the vertical metal organic chemical vapour deposition (MOCVD) reactor is simulated by using the finite element method (FEM). The effects of alternating current frequency, intensity, coil turn number and the distance between the coil turns on the distribution of the Joule heat are analysed separately, and their relations to the value of Joule heat are also investigated. The temperature distribution on the susceptor is also obtained. It is observed that the results of the simulation are in good agreement with previous measurements.