全息光栅实时显影监测曲线的理论模拟

在特定的工艺条件下,光刻胶的非线性效应非常显著;合理地利用非线性效应,能够制作出近似矩形的全息光栅掩模。为了分析清楚非线性效应对光栅沟槽成形的作用机理,有必要建立一个显影理论模型。模拟得到的光栅轮廓和实验样片的扫描电子显微镜照片结果很吻合。根据这个模型,进而使用光栅严格理论,得到其主要特征与实时监测实验曲线一致的理论模拟监测曲线。理论分析和实验证实,该模型基本表征了工艺条件对光栅沟槽形状的影响,并揭示了光刻胶呈现显著非线性效应时,必然对应着明暗条纹中心位置之间的显影刻蚀速率相差很大。这个模型为全息光栅的工艺研究提供了一个有效的理论分析工具。     

全息光栅制作中的实时潜像自监测技术

介绍了一种实时监测全息光栅曝光过程的新方法。在曝光过程中,光刻胶折射率的空间分布发生微小变化,由此形成的潜像光栅同时对记录光束产生衍射(自衍射),探测一个非零级次的衍射强度的变化就可对曝光过程实时监测。实验证明,这种技术能灵敏、客观地探测出样片之间由于个性差异所导致的最佳曝光量的漂移,制作者可以借此对曝光时间做实时补偿。发现自监测曲线之线性区的末端存在着一个明显的最佳曝光参考点,紧接其后是一个最佳曝光可选择区。采用了一个曝光模型,其模拟结果和实验中得到的自监测曲线能很好地吻合。理论分析证实,根据实时监测曲线的相对幅值来优化最佳曝光量的方法是很合理的,这种实时自监测是一种非常简单、能有效控制曝光量的技术。     

Cherenkov terahertz radiation from Dirac semimetals surface plasmon polaritons excited by an electron beam

We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band.     

亚太赫兹波折叠波导扩展互作用振荡器研究

对于亚太赫兹波段扩展互作用振荡器(EIO),本文采用折叠波导作为慢波谐振系统,研究了周期数对高频特性的影响,计算了特征阻抗、起振电流随周期数的变化规律,为有效降低起振电流提供了途径.在此基础上,采用PIC进行模拟研究,探讨了EIO在弱电流连续波和强电流脉冲工作方式下的注波互作用和输出特性,深入分析了EIO的周期数调谐、电压调谐的特性.在连续波工作时,EIO的输出功率约2.5 W;在脉冲工作方式下,通过电压调谐,EIO的输出功率约26-50 W,激发频率约105.26-105.31 GHz.采用慢走丝加工方法,探讨了高频系统的两种加工方式,测试了慢波系统的谐振特性、输出窗的传输特性,并与模拟结果进行了对比分析,验证了该加工方法在该频段的可行性和实用性,为实用型整管研究提高了重要依据.     

高电流密度圆柱状电子光学系统设计

设计了高电流密度圆柱状电子枪,并分析了枪体参数对电子注品质的影响;运用径向力平衡理论计算了聚焦磁场.三维模拟软件CSTPARTICLESTUDIO模拟显示,在枪体电极和空间电荷形成的静电场,以及聚焦磁场作用下,电子呈角向先变速后匀速螺旋状运动,其旋转半径始终与出射阴极面时的半径相同,从而在枪区和互作用通道内维持了注包络水平.模拟结果与设计理论相符.注平均电流密度达到24·4A/cm2,层流性良好,填充因子76·7%,流通率100%.     

扩展互作用谐振腔的模拟分析

 分析了扩展互作用谐振腔的工作原理、特点以及工作过程，并利用PIC粒子模拟程序对其进行了数值模拟，分析了阴极电压、电子注半径、谐振腔个数以及谐振腔周期长度对输出功率、频率及转换效率的影响。结果表明：当阴极电压为28.5~30.0 kV时，谐振腔能正常工作；当电子注半径为1.4 mm，谐振腔个数为4，阴极电压为29 kV时输出功率和转换效率最大，输出功率为128 kW，频率12.9 GHz，转换效率达37.93%；输出频率随谐振腔周期长度的变小而增大。     

Electron tunneling through double-electric barriers on HgTe/CdTe heterostructure interface

We investigate theoretically the carrier transport in a two-dimensional topological insulator of (001) HgTe/CdTe quantum-well heterostructure with inverted band, and find distinct switchable features of the transmission spectra in the topological edge states by designing the double-electric modulation potentials. The transmission spectra exhibit the significant Fabry-Pérot resonances for the double-electric transport system. Furthermore, the transmission properties show rich behaviors when the Fermi energy lies in the different locations in the energy spectrum and the double-electric barrier regions. The opacity and transparency of the double-modulated barrier regions can be controlled by tuning the modulated potentials, Fermi energy and the length of modulated regions. This electrical switching behavior can be realized by tuning the voltages applied on the metal gates. The Fabry-Pérot resonances leads to oscillations in the transmission which can be observed in experimentally. This electric modulated-mechanism provides us a realistic way to switch the transmission in edge states which can be constructed in low-power information processing devices.