Finite size effect on the Raman frequency of phonons in nano-semiconductors

A comprehensive study on Raman spectroscopy with different excitation wavelengths, sample sizes, and sample shapes for optic phonons (OPs) and acoustic phonons (APs) in polar and non-polar nano-semiconductors has been performed. The study affirms that the finite size effect does not appear in the OPs of polar nano-semiconductors, while it exists in all other types of phonons. The absence of the FSE is confirmed to originate from the long-range Fr¨ohlich interaction and the breaking of translation symmetry. The result indicates that the Raman spectra of OPs cannot be used as a method to characterize the scale and crystalline property of polar nano-semiconductors.     

基于隐马尔科夫模型的CPM信号盲Turbo均衡算法

针对高阶连续相位调制信号(CPM)盲均衡中存在的均衡性能较差以及不容易收敛等问题,从隐马尔科夫模型(HMM)的角度出发,建立一种新的EM-SOVA信道盲均衡方法,并结合Turbo均衡思想,提出了一种适用于高阶CPM信号的盲Turbo均衡算法。该算法通过将SOVA内嵌到EM算法的迭代过程中,有效改善了信道均衡效果,同时使用Turbo均衡的软信息迭代处理来进一步提高低信噪比条件下系统性能。理论分析和仿真结果表明,所提算法具有良好的盲均衡性能以及收敛性。     

基于SDR的5G功放数字预失真线性化平台

为了最大化信息吞吐量,信号带宽在不断增长,5G通信中RF发射器面临着一系列不断发展的挑战.对于射频收发链中数字预失真算法的研究,本文提出了一种基于软件定义无线电的功放数字预失真线性化平台,采用了宽带射频收发器ADRV9009和UltraScale+MPSoC,相对于传统的基于矢量信号发生器加矢量信号分析器构建的数字预失...     

高场磁共振成像1H/31P双调谐射频线圈研究进展

在众多可产生磁共振现象的原子核中,¹H核凭借其在生物体中含量高、磁共振信号强的优势,成为磁共振成像的主要研究对象．但其它杂核在生命科学相关研究中同样具有不可替代的独特性,如³¹P核广泛参与了生物体内的能量代谢过程,是非质子成像研究领域的重要内容．MRI向更高场强的发展使得杂核成像逐渐普及,其核心部件是高质量的¹H/³¹P双调谐射频线圈．本文总结了与¹H/³¹P双调谐射频线圈相关的研究与应用,展示了9.4 T下小鼠脑的质子磁共振成像及磁共振磷谱,并讨论了高场¹H/³¹P双调谐射频线圈的潜在应用价值．     

基于VO2的太赫兹各向异性编码超表面

设计了一种3层结构的太赫兹编码超表面,其顶部是嵌入VO₂的金属十字架结构,中间是聚酰亚胺,底部为纯金属.利用该编码超表面的各向异性特点,可以实现对正交极化波(x极化波和y极化波)的独立调控;通过在编码超表面中引入VO₂材料,改变其相变状态,可进一步增加调控的灵活性.对设计的超表面进行建模仿真和分析,结果表明:对于垂直入射的1 THz正交极化波, VO₂处于绝缘态时,设计的超表面可视为2 bit的各向异性编码超表面,产生模式为1和2的涡旋波; VO₂处于金属态时,设计的超表面可视为1 bit的各向异性编码超表面,产生对称的2束反射波和4束反射波.所提出的各向异性和相变材料结合的方法,实现了同一超表面上产生多种不同形式太赫兹波束的功能,一定程度上解决了超表面调控太赫兹波形式单一的问题,为实现能够灵活应用于多种场景的多功能编码超表面提供了参考.     

基于紫外激光瑞利散射大气密度测量的研究

大气密度的准确测量在气象、航空航天等领域都有重要的意义.本文介绍了一种适合于机载的基于紫外激光(波长266 nm)瑞利散射测量大气密度的系统,并针对平流层下层大气进行了分析、计算,讨论了激光器、ICCD参数以及系统结构对于测量结果的影响.     

基于GaSe差频产生8～19μm可调中红外辐射

利用Nd:YAG激光器抽运内腔KTP光学参量振荡器,得到了输出为2μm附近的双波长,并在满足Ι类相位匹配条件下,在GaSe中共线差频产生8～19μm连续宽调谐调的中红外辐射.在8.76μm处脉冲最大能量达33.66μJ,峰值功率7.4kW,光子转换效率达4.43%左右.分析了影响能量转化效率的原因,提出了补偿走离的措施.     

电光调Q 1064nm/532nm脉冲激光器

报道了一种用于产生THz波的电光调Q脉冲激光器,重复频率为1Hz、10Hz,输出1064nm、532nm可方便转换.当腔长310mm,输入能量为16J时,输出的1064nm调Q脉冲能量210mJ,电光转换效率1.3%,平均脉宽13ns,532nm脉冲能量110mJ,倍频效率50%,脉宽9~12ns.并对实验结果进行了分析和讨论.     

Efficient Compound-Cavity Eye-Safe KTP OPO at 1.57 μm Pumped by an Electro-Optic Q-Switched Nd：YAG Laser

An efficient high-energy eye-safe optical parametric oscillator （OPO） based on a type-Ⅱ non-critically phasematched KTP crystal is demonstrated. The KTP OPO is pumped by a quasi-cw diode side-pumped electrooptic Q-switched Nd：YAG laser in a compound-cavity configuration. The maximum output energy of the signal wavelength at 1.57 μm b 66.5 m J, corresponding to an electrical-to-optical conversion efficiency of 4.47% and an optical-to-optical conversion efficiency of 12.1%. The pulse width （FWHM） is about 3.6 ns with a peak power of 18.5 MW. The output energy is insensitive to repetition rate and demonstrates good stability.     

Low-loss terahertz waveguide with InAs-graphene-SiC structure

We demonstrate a low-loss terahertz waveguide based on the InAs-graphene-SiC structure. By analyzing the terahertz waveguide proposed in this paper, we can obtain that it is the characteristic of a low transmission loss coefficient(αloss≈0.55 dB/m) for fundamental mode(LP01) when the incident frequency is larger than 3.0 THz. The critical radii of the inside and outside cylinders have been found for the high-quality transmission. The large inside radius and the high transmission frequency result in a flat transmission loss coefficient curve. As a strictly two-dimensional material, the double graphene surface rings perform better to improve the quality of transmission mode. These results provide a new idea for the research of the long-distance THz waveguide.