Wireless terahertz light transmission based on digitally-modulated terahertz quantum-cascade laser

A wireless terahertz digital transmission link is demonstrated, in which a quantum-cascade laser and a spectrally-matched quantum-well photodetector serve as the emitter and receiver, respectively. An on-off modulation scheme is used. By directly amplitude modulating the laser emitting at 4.13 THz, a 1.0-Mbps pseudorandom signal is transmitted over a distance of 2.2 m.     

基于太赫兹时域光谱技术的伪色彩太赫兹成像的实验研究

提出了一种伪色彩太赫兹成像技术. 通过引入频域色彩区间积分, 建立了一套基于太赫兹时域光谱技术的伪色彩太赫兹成像系统, 实验分别研究了乳糖和对氨基苯甲酸两种不同白色化学粉末的伪色彩成像和灰度成像, 研究了不同颜色区间定义对伪色彩图像的影响, 讨论了利用不同频率信息成像系统所能达到的空间分辨率. 研究结果表明, 伪色彩成像技术可以将不同的物质信息同时成像在一张太赫兹图像中, 通过不同物质在太赫兹图像中呈现出的颜色差别来区分不同的物质及其分布. 克服了传统的太赫兹灰度成像技术中, 需要多张图像来区分不同的物质的问题, 提高了成像速度, 降低了筛选难度. 利用高频信息进行伪色彩成像, 可以将系统成像的空间分辨率提高到0.4 mm. 伪色彩成像方式可以更直观快捷地显示样品的基本属性, 对于实现太赫兹安检的初检和快速筛选具有重大的现实意义.     

Broadband terahertz spectroscopy

An overview of the major techniques to generate and detect THz radiation so far,especially the major approaches to generate and detect coherent ultra-short THz pulses using ultra-short pulsed laser,has been presented.And also,this paper,in particularly,focuses on broadband THz spectroscopy and addresses on a number of issues relevant to generation and detection of broadband pulsed THz radiation as well as broadband time-domain THz spectroscopy (THz-TDS) with the help of ultra-short pulsed laser.The time-dom...     

Ion-nanotube terahertz oscillator

We report the intriguing dynamics of a potassium ion interacting with a 16 A carbon nanotube. The ion induces a strong dielectric response in the nanotube wall that can be described through a self-consistent tight-binding method. The polarization of the nanotube was found to play a critical role in the ion-nanotube interaction, which exhibits a low access barrier of only 1.05 kcal/mol and a deep, attractive well with a depth of about 30 kcal/mol. An ion bound in the nanotube is predicted to oscillate at a frequency of about 0.4 terahertz, dragging the electrons of the nanotube along. Besides its appealing nature in low-dimensional physics, such a nano-oscillator may serve as a room temperature terahertz wave detector.     

Optical terahertz bullets

Optical generation of broadband terahertz radiation in a system of resonant anisotropic molecules with a permanent dipole moment has been investigated taking into account the transverse dynamics of pulses. It has been shown that, if the carrier frequency of a femtosecond optical signal is higher than the eigenfrequency of a selected molecular transition by such a value that the spectrum of the pulse, owing to its finite length, covers the resonance transition, the generation occurs in the filamentation regime followed by transformation of the filaments into stable optical terahertz bullets localized in all directions. In this case, the energy generation efficiency can be as high as ～10^?3.     

Active terahertz metamaterials

In this paper we present an overview of research in our group in terahertz (THz) metamaterials and their applications. We have developed a series of planar metamaterials operating at THz frequencies, all of which exhibit a strong resonant response. By incorporating natural materials, e.g., semiconductors, as the substrates or as critical regions of metamaterial elements, we are able to effectively control the metamaterial resonance by the application of external stimuli, e.g., photoexcitation and electrical bias. Such actively controllable metamaterials provide novel functionalities for solid-state device applications with unprecedented performance, such as THz spectroscopy, imaging, and many others.     

Superluminal terahertz pulses

In femtosecond terahertz-pulse (T-ray) imaging of metal structures with dimensions of the order of the wavelength, it is observed that the T rays propagate faster than the vacuum speed of light. In the case of apertures this can be understood as a waveguide effect in which superluminal velocities are expected close to the cutoff frequency. However, the effect is also observed close to knife edges and in propagation past thin metal wires.     

Quasi-optic terahertz imaging

We demonstrate quasi-optical, diffraction-limited two-dimensional image production by means of reflected pulses of terahertz (THz) radiation. A spherical mirror is used to form a real one-to-one THz image of two 1-mm-diameter steel spheres, which is then scanned over a THz receiver. Diffraction-limited spatial (cross-range) resolution and THz pulse range resolution are simultaneously observed.     

高速太赫兹探测器

太赫兹(terahertz,THz)技术在高速空间通信、外差探测、生物医学、无损检测和国家安全等领域具有广阔的应用前景.能响应1 GHz调制速率以上THz光的高速THz探测器是快速成像、THz高速空间通信、超快光谱学应用技术和THz外差探测等领域的核心器件.传统的THz热探测器难以实现高速工作,而基于半导体的THz探测器在理论上可实现高速工作.光导天线具有超快的响应速度,可实现常温和宽谱探测;肖特基势垒二极管混频器、超导-绝缘体-超导混频器和超导热电子混频器具有转换效率高、噪声低等优点,可用于高速THz空间外差和直接探测;基于高迁移率二维电子气的天线耦合场效应晶体管灵敏度高、阻抗低,可实现常温高速THz探测;THz量子阱探测器是一种基于子带间跃迁原理的单极器件,非常适合高频和高速探测应用,亚波长金属微腔耦合机理可显著提高器件的工作温度及光子吸收效率.本文对上述几种高速THz探测器进行了综述并分析了各种探测器的优缺点.     

Rapid-phase modulation of terahertz radiation for high-speed terahertz imaging and spectroscopy

Rapid voltage-controlled phase modulation of cw terahertz (THz) radiation is demonstrated. By transmitting an infrared beam through a lithium niobate phase modulator the phase of the THz radiation, which is generated by the photomixing of two infrared beams, can be directly modulated through a 2pi phase shift. The 100 kHz modulation rate that is demonstrated with this technique is approximately 3 orders of magnitude faster than what can be achieved by mechanical scanning.     

New terahertz dispersive device for single-shot spectral measurements of terahertz pulse

A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.     

基于太赫兹量子阱探测器的太赫兹量子级联激光器发射谱研究

采用一个光谱匹配的太赫兹(THz)量子阱探测器(QWP)研究了一激射频率约为41 THz的THz量子级联激光器(QCL)在不同驱动电流下的发射谱,分析了测量得到的发射谱谱型和谱峰位置,根据测量的发射谱估算了太赫兹量子级联激光器发射功率随驱动电流变化的情况,从而得到了THz QCL激射的电流密度范围及其阈值电流密度.文中还研究了THz QWP在不同温度下对THz QCL 激光辐射的响应特性.研究结果表明,THz QWP在表征THz QCL的发射谱方面是一种很好的探测器,并有望成为未来THz通信中的接收装置. 关键词： 太赫兹量子阱探测器 太赫兹量子级联激光器 太赫兹通信 Fourier变换红外光谱     

Typesetting of terahertz waveforms

We demonstrate programmable generation of temporally shaped terahertz waveforms in LiNbO3 by spatially shaping the beam profile of femtosecond excitation laser pulses with a spatial light modulator. The generated terahertz waveforms have amplitudes that are approximately proportional to the first spatial derivative of the excitation beam profile.     

Dynamically phase-matched terahertz generation

We present the generation of intense terahertz pulses by optical rectification of 780 nm pulses in a large area gallium phosphide crystal. The velocity mismatch between optical and terahertz pulses thereby limits the bandwidth of the terahertz pulses. We show that this limitation can be overcome by a dynamic modification of the refractive index of the gallium phosphide crystal through generation of hot phonons. This is confirmed by excellent agreement between experimental results and model calculations.     

基于太赫兹量子阱探测器的太赫兹量子级联激光器发射谱研究

采用一个光谱匹配的太赫兹(THz)量子阱探测器(QWP)研究了一激射频率约为41 THz的THz量子级联激光器(QCL)在不同驱动电流下的发射谱,分析了测量得到的发射谱谱型和谱峰位置,根据测量的发射谱估算了太赫兹量子级联激光器发射功率随驱动电流变化的情况,从而得到了THz QCL激射的电流密度范围及其阈值电流密度.文中还研究了THz QWP在不同温度下对THz QCL 激光辐射的响应特性.研究结果表明,THz QWP在表征THz QCL的发射谱方面是一种很好的探测器,并有望成为未来THz通信中的接收装置.     

Synthetic phased-array terahertz imaging

We demonstrate terahertz (THz) imaging with enhanced spatial resolution by a synthetic phased array. A single mirror is used to separately form two different coherent, diffraction-limited THz images of the same point source. The two images are combined to yield a 4x resolution-enhanced image of the source in one dimension.     

High-performance fiber-laser-based terahertz spectrometer

We have developed a rapid scanning terahertz (THz) spectrometer based on a synchronized two-fiber-laser system. When the system is set to the asynchronous optical sampling mode, THz spectra extending to 3 THz can be acquired within 1 μs at a signal-to-noise ratio of the electric field of better than 20. Signal averaging results in a dynamic range of more than 60 dB, and frequency components of more than 4 THz can be detected. When the lasers are set to the same repetition rate, electronically controlled optical sampling at a rate of 2.5 kHz is demonstrated, making the system versatile for different spectroscopic applications. Finally, we compare the THz emission spectra of a photoconductive switch that is pumped at 780 nm and a nonlinear DAST crystal excited at 1550 nm. We find that the spectral range of the spectrometer is significantly enhanced at higher frequencies, while the dynamic range remains constant.     

太赫兹人工电磁媒质研究进展

近年来, 随着太赫兹科学技术的发展, 越来越多的科学家向太赫兹间隙这一传统空白领域发起挑战. 其中, 人工电磁媒质因为能够设计太赫兹波段中紧缺的功能器件而受到广泛关注. 近年来, 对人工电磁媒质尤其是太赫兹方面的研究进展突飞猛进. 人工电磁媒质的性质不仅仅由其构成材料决定, 更与其结构单元的形状和空间排布密切相关. 本文介绍了人工电磁媒质在太赫兹波段的发展、原理、设计和应用, 并着重介绍完美吸波器和人工表面等离激元, 为太赫兹波段功能器件的研究提供了参考, 并对可能的发展方向予以展望.     

Whispering-gallery mode terahertz pulses

We report what is to our knowledge the first observation of a subpicosecond terahertz (THz) pulse propagating as a superposition of the whispering-gallery modes (WGMs) of a dielectric cylinder. The WGM THz pulses are coupled into and out of a 5-mm-diameter silicon cylinder via a 100-mum -thick, single-mode silicon slab waveguide. We observed two round-trip cylindrical cavity pulses from this coupling structure, which cover a continuous frequency range from 0.4 to 1.8 THz. The coupled-mode equations are used to analyze this system and give reasonably good agreement with the experiment in both the frequency and the time domains.