ZnTe晶体对太赫兹波的电光响应及极化匹配

给出了ZnTe电光晶体折射率和吸收系数随太赫兹波频率而变化的计算曲线,比较了太赫兹波在ZnTe中传播时的相速度和群速度。通过与太赫兹频率和晶体厚度相关的电光效率响应函数,理论计算了ZnTe电光晶体对太赫兹脉冲的探测电光响应,得到了晶体厚度与探测到的太赫兹频谱宽度的定性关系,从计算结果中找到了ZnTe电光晶体在5.3 THz和6.2 THz等多个频点的探测盲点,这些探测盲点来自于ZnTe电光晶体与相应频点太赫兹波的栅格共振吸收。结合自制的大口径太赫兹光导天线和1 kHz脉冲重复频率的太赫兹时域光谱实验系统,通过差分探测技术,从实验上得到了太赫兹波极化方向与〈110〉型ZnTe晶体晶轴方向的六个最佳匹配角度,给出了太赫兹电场最大值随晶轴与太赫兹波极化方向之间夹角变化的曲线及经验公式,这将有利于在实践中对该现象的深入理解和对探测灵敏度的有效提高。     

二氧化钛光子晶体波导的太赫兹波传输特性

本文应用时域有限差分法研究了二维二氧化钛光 子晶体波导的禁带范围和太赫兹波的 传输特性,分别设计了带隙宽度为0.226 THz 、0.2728 THz和0.316 THz的直线型、直角型和T 型二氧化钛光子晶体波导结构。研究发现,相比传统波导,本文设计的二维二氧化钛光子晶 体波导不仅在直线路径中有较高的太赫兹波传输效率,而且在转角的路径中也有很高的太赫 兹波传输效率。此研究结果为太赫兹器件的设计和制作提供重要理论依据,为高速宽带无线 通信系统的发展提供重要理论借鉴。     

氧化铝晶体的太赫兹光谱特性研究

利用太赫兹时域光谱(THz-TDS)技术研究了氧化铝(Al2O3)在宽带太赫兹波范围(0.2～3.0 THz)内的光谱特性.改变晶体光轴与太赫兹脉冲偏振方向间的夹角(方位角),得到了Al2O3晶体在不同方位角下的太赫兹时域谱,计算了Al2O3晶体o光和e光的折射率和吸收系数,并画出了Al2O3晶体在太赫兹波段的折射率椭...     

基于LiNbO3光整流效应的高峰值功率太赫兹源

基于光整流效应,通过倾斜泵浦光波前(TPFP)在铌酸锂晶体中实现相位匹配,是一种有效的产生太赫兹辐射的方法。建立了一种更完备的基于波面倾斜的产生太赫兹波的理论模型,用于分析不同泵浦光偏振下产生太赫兹波的转换效率。搭建了基于铌酸锂晶体光整流效应的高峰值功率太赫兹源和太赫兹时域光谱系统,并利用太赫兹面阵探测器对获得的太赫兹辐射进行了分析。结果表明,所获得的太赫兹辐射单脉冲峰值功率达到0.56 MW,频谱宽度为0.1 THz~2 THz,转换效率为0.56‰,与理论模拟结果相符。     

基于太赫兹时域光谱技术的水蒸气传输特性研究

为了评估太赫兹波在空间通信、雷达、遥感等方面的潜在应用,需要研究太赫兹波在大气中的传输特性。由于0.1～2 THz的太赫兹波在大气中传输的主要衰减来自水蒸气,采用太赫兹时域光谱技术(THz Time-Domain Spectroscopy,THz-TDS),在2 m长的太赫兹传输行程中对不同湿度的空气进行了透射光谱测量,获得了水蒸气在0.1～2THz频率范围内的吸收谱、传输率和弱衰减窗口。     

光控光子晶体太赫兹波调制器消光比的研究

光控太赫兹波调制器在未来的THz通信中具有重要作用,消光比是太赫兹波调制器的主要性能指标,文中研究了基于二维正方晶格光子晶体太赫兹波调制器晶格变化对调制器消光比的影响,选取光子晶体介质柱的半径作为结构参量,利用基于FDTD的Rsoft软件进行仿真计算,结果表明,将谐振腔正上方介质柱的半径缩小一定数量时,可以提高调制器的消光比。     

消色差复合宽带太赫兹波片的优化设计

采用模拟退火算法设计了0.2～2.0THz和0.2～3.0THz两个波段下的消色差复合太赫兹λ/4波片,在0.2～2.0THz波段内实现了波片相位延迟偏差小于2%,在0.2～3.0THz波段内波片相位延迟偏差小于4%。系统分析了不同石英玻片个数对消色差复合太赫兹波片的消色差性能以及厚度和损耗等关键参量的影响。分析表明,随着石英玻片个数的增加,波片的消色差性能也会变好,在相应太赫兹波段相位延迟失谐量也随之减小;但同时,波片的厚度也随之增加,导致对太赫兹波的损耗增加。在0.2～2.0THz和0.2～3.0THz范围内,太赫兹λ/4波片采用5个玻片为最佳,此时可以获得较好的消色差性能,同时波片的厚度和损耗也在可实际应用范围内。     

太赫兹超常材料及应用

超常材料具有人工设计的结构,并有自然材料所不具备的超常物理性质。超常材料的电磁响应灵活可调,对太赫兹(THz)技术意义非凡。THz超常材料的实现和迅速发展为太赫兹技术的发展和应用带来了新的机遇。总结了THz波段超常材料的研究进展,包括THz波段超常材料的构造及制备、基于超常材料的THz波器件以及超常材料在THz波技术中的其他应用。     

基于全光纤高相干参量过程差频产生太赫兹

实现了基于全光纤参量过程的高相干光差频产生太赫兹波。采用超长腔锁模光纤激光器产生的窄谱宽、低重复 率的光做泵浦,利用光纤参量过程产生一对高相干的种子光。经功率放大后在DSTMS 有机晶体中差频产生1.25THz 的 太赫兹波,脉冲宽度小于700ps,谱宽小于512MHz。     

基于全光纤高相干参量过程差频产生太赫兹

实现了基于全光纤参量过程的高相干光差频产生太赫兹波。采用超长腔锁模光纤激光器产生的窄谱宽、低重复率的光做泵浦,利用光纤参量过程产生一对高相干的种子光。经功率放大后在DSTMS有机晶体中差频产生1.25THz的太赫兹波,脉冲宽度小于700ps,谱宽小于512MHz。     

硅棱镜耦合输出THz波参量振荡器的实验研究

利用一块MgO:LiNbO3晶体,采用Si棱镜耦合出射方式构成太赫兹(THz)波参量振荡器,实现了高效可调谐的THz波输出,调谐范围为0.95～2.10THz。在1.80THz处,当泵浦能量为101mJ时,产生的THz波平均功率为580nW,THz波单脉冲能量为58nJ,THz波能量转换效率为5.74×10-7;同时产生的Stokes能量为2.7mJ。实验中,观察到了一阶和二阶Stokes光,一阶Stokes光与泵浦光的频差等于产生的THz波的频率。     

Compact Tunable Narrowband Terahertz-Wave Source Based on Difference Frequency Generation Pumped by Dual Fiber Lasers in MgO:LiNbO<Subscript>3</Subscript>

We demonstrate a high-average-power, single longitudinal-mode, and tunable terahertz (THz)-wave source based on difference frequency generation (DFG) in a MgO:LiNbO₃ (MgO:LN) crystal. The waves for DFG are generated using a pair of Yb-doped pulsed fiber lasers with a master oscillator power fiber amplifier configuration. The average power of the THz-wave output reaches 450 μW at 1.07 THz (280 μm) at a linewidth of 7.2 GHz, and the tunability ranges from 0.35 to 1.07 THz under the pulse repetition frequency of 500 kHz. A short burn-in test of the THz wave is also carried out, and the output power stability is within ± 5% of the averaged power without any active stabilizing technique. The combination of MgO:LN-DFG and stable and robust fiber laser sources is highly promising for the development of high-average-power THz-wave sources, particularly in the high transmission sub-THz region. This approach may enable new applications of THz-wave spectroscopy in imaging and remote sensing.     

表面出射太赫兹波参量振荡器的设计与增强输出

利用一台多纵模调Q Nd:YAG激光器泵浦的浅表垂直发射太赫兹波参量振荡器参量产生了高功率可调谐太赫兹波辐射。推导了非共线相位匹配条件下的有效参量增益长度以优化太赫兹波参量振荡器参数。实验测得太赫兹波的调谐范围为0.77~2.83 THz。当泵浦功率密度为222.3 MW/cm2时,在1.78 THz处太赫兹波的最大输出能量为347.8 nJ/pulse,对应的能量转化效率为3.9110-6。太赫兹波在垂直方向上的远场发散角为0.020 4 rad,在水平方向上为0.006 8 rad。     

Kilowatt-peak Terahertz-wave Generation and Sub-femtojoule Terahertz-wave Pulse Detection Based on Nonlinear Optical Wavelength-conversion at Room Temperature

Intense Terahertz (THz)-wave generation and highly sensitive THz-wave detection were obtained by wavelength conversion with nonlinear optical susceptibility χ⁽²⁾ of LiNbO₃ crystals. Maximum peak output of about 50 kW (5 μJ/pulse) was demonstrated in an injection-seeded THz-wave parametric generator pumped by post-amplified emission from a microchip Nd:YAG laser. Using the sub-nanosecond pulse duration of the laser proposed herein provides effective mitigation of stimulated Brillouin scattering in LiNbO₃, producing higher gain for wavelength conversion between near-infrared (near-IR) pump light and THz waves. Monochromatic THz radiation was obtained in the continuous tuning range of 0.7–2.9 THz. Additionally, highly sensitive THz-wave detection was demonstrated based on up-conversion from THz waves to near-IR light as well as efficient THz-wave generation. The signal generated with non-collinear phase-matching condition showed spectroscopic detection on the screen apart from the LiNbO₃ crystal. Highly sensitive detection with minimum energy of about 80 aJ/pulse (0.8 μW at peak) and a large dynamic range of more than 100 dB were achieved in this experiment.     

Widely Frequency-Tunable Terahertz Wave Generation and Spectroscopic Application

The THz-wave generator based on the resonance of phonon-polaritons in GaP enabled THz spectral measurements of organic molecules like DNA/RNA-related molecules in wide frequency range (0.6–5.8 THz). High spectral purity of the generated THz-wave enables even the detection of defect structures of organic compounds, and will give a new tool for molecular sciences. We demonstrated THz imaging of a liver cancer. The THz-wave generator can be made small-size, light-weight system.     

337μm连续太赫兹激光透射成像

针对太赫兹面阵探测器件发展不成熟的现状,利用二维移动平台,对合作目标进行了连续太赫兹波的扫描成像实验.太赫兹波的扫描成像结果可以显示遮蔽物内的物件,这是可见光和红外所不能完成的.通过减小激光光斑、提高成像分辨率,可更清晰地表现隐藏物件的轮廓,有助于辨别该物件.实验还测量了337μm太赫兹激光对典型物质的穿透特性,其中包括对近红外和中红外具有很好屏蔽作用的伪装网材料.测量结果显示:337μm太赫兹激光对包装泡沫穿透能力很强,适合包装物的无损检查;对干枯树叶和新鲜树叶透射差别较大,对野外探测具有启示意义;对某些伪装网具有一定的穿透能力,为某些军事应用提供了可能.     

0.34 THz折叠波导行波管设计及流通管实验

以0.34 THz折叠波导行波管为研究对象,分析了慢波结构的色散特性、耦合阻抗、冷损耗特性和工作模式等,并按优化后折叠波导慢波结构的要求设计电子光学系统,进行流通管实验,得到电子注通过率大于80%的实验结果。最后对输入输出结构进行优化设计,满足中心频率为0.345 THz,带宽大于10 GHz,输出功率大于20 mW的0.34 THz折叠波导行波管设计要求。     

Enhancement of CW THz Wave Power Under Noncollinear Phase-Matching Conditions in Difference Frequency Generation

We investigated methods for improvement of continuous-wave (CW) terahertz (THz) output power by laser diode (LD) pumping in noncollinear phase-matched difference frequency generation (DFG). The effects of interaction length and beam spot size of input lasers (near-IR) in GaP crystals were studied. The THz wave power dependence on various sizes of GaP crystals was investigated and it was observed that an output power of 4 nW was obtained with a 20 mm long GaP crystal at 1.5 THz. Also, the THz wave absorption coefficient was dominant for longer GaP crystals at high frequencies (above 2.5 THz). The THz wave power dependence on beam spot size (1.2 mm–300 $mu{rm m}$) of near-IR lasers at 1.62 THz was studied, and an improvement of THz wave power being seen with a 500 $mu{rm m}$ beam spot size, while the beam divergence effect was dominant for beam spot sizes below 500 $mu{rm m}$.      

THz-wave absorption by field-induced carriers in pentacene thin-film transistors for THz imaging sensors

Innovative sensing systems based on THz electromagnetic waves have been attracting a great deal of attention. Although many THz detectors have been developed over the years, it is currently difficult to manufacture low-cost THz sensing/imaging devices. In the present study, we propose to use organic field-effect transistors (OFETs) and small potential fluctuation against the carriers within them (N. Ohashi, H. Tomii, R. Matsubara, M. Sakai, K. Kudo, M. Nakamura, Appl. Phys. Lett. 91 (2007) 162105). We use THz time-domain spectroscopy for OFETs in which the carrier density in the pentacene active layer is modulated by the gate bias. We found evidence that the accumulated free holes in pentacene films can be excited by THz photons to overcome the surrounding barriers in the fluctuating potential. The Drude–Lorentz model could not account for the shape of the absorption spectra, which suggests that the holes are weakly restricted by the potential fluctuation. The integrated absorption intensity was proportional to the transfer characteristics of the OFETs. The present findings represent an important step toward developing a new class of THz-wave sensors.