THz技术的应用及展望

自20世纪80年代中期以来，THz辐射的研究取得了重要的进展，文章介绍和讨论了以THz辐射为探测光源的时域光谱测量在基础物理，信息材料，化学和生物材料研究中的应用，以及THz成像和THz“雷达”技术在材料研究，安全检查和生物医学等领域的应用前景。     

OPTICAL PROPERTIES OF ZnO COMPOSITE NANOPARTICLES

We have synthesized core/shell structure ZnO composite nanoparticles by surface chemical modification. This new composite material shows a large optical gap redshift compared with the homogeneous ZnO nanoparticles. The visible photoluminescence ranging from blue to red in color with fast decay time may be as signed to the interfacial bound-exciton-like emission.     

从光子晶体效应到表面等离子波的实时演变

文章报道了激光诱导太赫兹表面等离子谐振效应。采用激光抽运-太赫兹波探测技术，实时改变单晶硅中的载流子浓度，使其介电特性从类绝缘体演变为类金属导体，以支持表面等离子谐振效应，进而实现太赫兹波在周期性亚波长单晶硅孔阵列中的实时可控制谐振增强传输。同时还通过实验观测到太赫兹波从光子晶体效应到表面等离子波的实时演变。文章作者采用Fano模型对实验结果进行模拟分析，获得了与实验数据一致的理论拟合。     

Entanglement evolution of three-qubit mixed states in multipartite cavity—reservoir systems

We analyze the multipartite entanglement evolution of three-qubit mixed states composed of a GHZ state and a W state.For a composite system consisting of three cavities interacting with independent reservoirs,it is shown that the entanglement evolution is restricted by a set of monogamy relations.Furthermore,as quantified by the negativity,the entanglement dynamical property of the mixed entangled state of cavity photons is investigated.It is found that the three cavity photons can exhibit the phenomenon of entanglement sudden death(ESD).However,compared with the evolution of a generalized three-qubit GHZ state which has the equal initial entanglement,the ESD time of mixed states is later than that of the pure state.Finally,we discuss the entanglement distribution in the multipartite system,and point out the intrinsic relation between the ESD of cavity photons and the entanglement sudden birth of reservoirs.     

使用太赫兹技术研究航天飞机失事的原因

太赫兹脉冲成像技术被应用于航天飞机隔热层泡沫材料中缺陷的探测．通过对泡沫样品的各个层面进行逐点扫描，得到每个点太赫兹脉冲的时域波形，然后利用多种图像处理手段分析波形的变化，判断出不同层面缺陷的大小、形状、位置和种类．太赫兹成像技术作为一种可以提供多维信息的新兴无损探伤技术，将可能被美国宇航局应用到以后的发射过程中的安全检查中。     

Terahertz Radiation from Large Aperture Bulk Semi-insulating GaAs Photoconductive Dipole Antenna

We report the experimental results of a large-aperture biased semi-insulating GaAs photoconductive dipole antenna, with a gap of 3mm between two Au/Ge/Ni electrodes, triggered by 80Ohm Ti-sapphire laser pulses with 82 MHz repetition rate. A direct comparison is made between insulated GaAs dipole antenna with a Si3N4 layer and bare GaAs dipole antenna. Both the current in the antenna and the radiation amplitude present as linear to the exciting power when the applied, voltage is fixed. The Si3N4 insulated GaAs dipole antenna can hold higher biased voltage than a normal GaAs dipole antenna; its terahertz radiation generation efficiency is significantly higher than that of a normal GaAs dipole antenna.     

SPECTROSCOPIC INVESTIGATION ON THE PROPERTIES OF VISIBLE AND NEAR INFRARED EMISSIONS IN Tm3+, Ho3+ Co-DOPED YVO4 CRYSTALS

With the help of absorption and fluorescence spectra, the spectroscopic properties of Tm³⁺, Ho³⁺:YVO₄ crystals have been investigated under different dopant concentrations. The absorption results show that the maximum absorption in the spectral range of currently available powerful laser diodes (LD) is at 796 nm, corresponding to the transition ³H₆→³H₄ of Tm³⁺ in the crystals. Upon the excitation with a LD at 808 nm, we have detected ten fluorescence bands in the spectral range spanning from visible to infrared. In visible region 4 upconversion bands have been observed centered at 475, 547, 660, and 701 nm. Discussions of the energy transfer processes suggest that cross relaxations and excited absorptions with the involvement of Tm^{3+ 3}F₄, ³H₅ and Ho^{3+ 7}I₅ states are responsible for the four upconversion emissions. Comprising the relative integrated intersities of 2 μm (Ho³⁺: ⁵I₇→⁵I₈) and 1.8 μm (Tm³⁺: ³F_4→³H₆) bands we have observed an efficient energy transfer from Tm³⁺ (³F₄) to Ho³⁺ (⁵I₇). Examination of the ratios of the intensity of 2 μm band to that of 1.8 μm band as a function of the ratios of Tm³⁺ concentration (c_Tm) to Ho³⁺ concentration (c_Ho) indicates that small concentration ratios (c_Tm/c_Ho) lead to high efficient energy transfers of Tm³⁺(³F₄)→Ho³⁺(⁵I₇).