Sub-Doppler and Doppler spectroscopy of DCN isotopomers in the terahertz region: ground and first excited bending states (v1v2v3)=(0 1 0)

The rotational spectra of the deuterium cyanide isotopic species DCN, D¹³CN, DC¹⁵N, and D¹³C¹⁵N were recorded in the vibrational ground and first excited bending state (v₂=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3-10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the ¹⁴N nucleus in DCN and D¹³CN for transitions as high as J=10←9. Additional high JR-branch (J=25←24 to J=28←27) transitions around 2 THz and direct l-type (ΔJ=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D¹³C¹⁵N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin-rotation coupling constants of the ¹⁴N nucleus for DCN and D¹³CN. The hyperfine structure due to the D, ¹³C, and ¹⁵N nuclei have not been resolved, but led to a broadening of the observed saturation dips.     

WIDE RANGE DETECTOR USING PARABOLIC CYLINDRICAL MIRROR FOR THz APPLICATIONS

A new, wide-band, high-speed and high-sensitivity THz detector has been developed. The prototype detector consists of a parabolic cylindrical mirror, a long wire antenna and a Schottky barrier diode. Direct detection measurements have shown a stable sensitivity of 150 ± 50 V/W for 1–2 THz without any adjustments. The long wire antenna was fixed at the focus of parabolic cylindrical mirror then it has been realized less operation steps, easy coupling to the external THz signals and a dramatic enhancement in the practicality of this system. The optically polished mirror and frosted surface one showed comparable sensitivities, thus easy polishing and less cost mirror fabrication can be applied for this system. The radiation pattern showed a maximum radiation angle of approximately 23° with its dominant main lobe, which was attributed to the wire antenna character and confirmed good agreements with classical antenna theory.     

TERAHERTZ QUALITY CONTROL OF POLYMERIC PRODUCTS

We report on experiments that evaluate the potential of terahertz (THz) time-domain spectroscopy (TDS) for quality control of polymeric compounds. We investigate specimens out of a polyethylene compound with silver-coated titanium dioxide nanospheres and a glass-fiber reinforced epoxy composite. We further examine an industrial polymer product produced by injection molding. Our data demonstrates that THz imaging is a powerful tool for contactless quality control in the polymer industry.     

Charge transport in anodic TiO2 nanotubes studied by terahertz spectroscopy

We report on the photoelectrochemical and terahertz measurements, of the charge transport properties of 1 μm thick self‐organized TiO₂ nanotube layers, prepared by the anodization of titanium. We provide evidence regarding the complexity of electron transport, and dynamics in the nanotubes. Shortly after photoexcitation, charge mobilites in amorphous and crystalline nanotubes are similar, but still lower compared to the bulk anatase. The mobility subsequently decreases due to trapping‐detrapping processes. The recombination rate in anatase nanotubes is much slower than in the amorphous ones, enabling the material to reach an internal photon to electron conversion efficiency exceeding 60%.     

两个二亚胺-铜(Ⅰ)-膦配合物的合成、结构和太赫兹时域光谱（英文）

本文报道了2个新的Cu(Ⅰ)配合物:[Cu(PPh3)2(dppz)]I(1)(PPh3=三苯基膦,dppz=二吡啶并[3,2-a∶2′,3′-c]吩嗪)和[Cu2(dppm)2(dppz)2]Cl2(2)(dppm=双(二苯基膦)甲烷)的合成,并通过X射线单晶衍射、元素分析、核磁共振氢(膦)谱、荧光光谱和太赫兹时域光谱对其进行了分析和表征。分析结果显示配合物1是一个单核配合物,中心Cu(Ⅰ)离子与2个含膦配体(PPh3)和1个含氮配体(dppz)进行配位,形成了一个扭曲的四面体结构。与1不同的是,配合物2是由CuCl,dppm和dppz以1∶1∶1的比例混配得到的双核配合物。其中,双膦配体dppm作为桥联配体,连接了2个Cu(Ⅰ)离子。荧光光谱表明所有的发射峰均源于金属到配体的电荷转移跃迁(MLCT)。同时,使用太赫兹时域光谱技术表征了2种配合物以及相应的配体。     

Terahertz radiation generation by beating of two spatial-Gaussian lasers

Terahertz radiation generation is proposed based on beating of two spatial-Gaussian lasers in a periodic density plasma, where a transverse component of current is realized that resonantly excites the radiation with efficiency ∼10⁻³. Importance of laser-beam-width, amplitude and periodicity of density structure is discussed for the efficient THz generation.     

Vibrational spectra of chloroform, freon-11 and selected isotopomers in the terahertz region

The fundamental bands of the CCl₃ asymmetric deformation modes of selected isotopomers of chloroform (CHCl₃) and freon-11 (CFCl₃) have been measured in a static cell at ambient temperature using a laser-based source of tunable radiation in the terahertz region of the electromagnetic spectrum. The analysis of the rotational contours of the bands enabled the derivation of the fundamental frequencies with an accuracy of better than 3 GHz.     

不同中心波长飞秒脉冲激发InAs表面辐射太赫兹波的机理研究

研究了p型(100)InAs在不同中心波长飞秒激发光(750—850nm)作用下的太赫兹(THz)波辐射特性.这种太赫兹辐射的光谱性质与光学Dember效应密切相关，飞秒脉冲激发下产生的载流子在InAs表面的Dember场内做加速运动，从而辐射出THz电磁波.实验结果表明：不同中心波长的激发光作用下，InAs表面产生的Dember电场、光生载流子浓度、谷间散射效应以及处于不同状态的载流子数目都发生了变化，因而激发出太赫兹波的功率、振幅、频谱分布和有效谱宽是不同的.这项研究将有利于THz时域光谱技术以及实验     

Monte Carlo Study of Terahertz Radiation from InAs

In this paper we investigated the THz radiation dynamics in InAs using the ensemble Monte Carlo method. Our simulations indicated that THz pulse shapes (temporal waveforms) are closely related with the pump laser fluence. The sharp, negative peak of a THz pulse may result from the electron intervalley transfers from center valley to satellite valleys. Our numerical results show that higher laser fluence is an advantage in enhancing the output of high frequency components. The spato-temporal distributions of photo-Dember fields on the semiconductor surface were also analyzed.     

MgF2单晶的THz光谱研究

利用THz时域光谱技术对MgF₂晶体(样品1)和MgF₂：Co晶体(样品2)在0.5—2.5 THz的吸收特性进行了研究.在0.5—2.5 THz波段，样品1吸收系数α(ν)随频率ν增加而增大，最大值为24 cm^-1.样品2的吸收系数比样品1大得多，Co掺杂使晶格吸收带边向低频移动，而且样品2在1.9 THz有吸收峰，吸收系数达到70 cm^-1，由此求出F^--Co²⁺离子键伸缩振动的键力常数K为3.40×10^-2　N/cm.这一结果表明，THz光谱分析有可能成为研究晶体化学键的一种重要手段.利用光学常数之间的关系计算了两个样品在0.5—2.5 THz的介电函数的实部ε₁(ν)，得到样品1的ε₁(ν)值在4.67至4.73之间，样品2的ε₁(ν)值在4.62至5.01之间. 关键词： THz辐射 光谱 2晶体')" href="#">MgF₂晶体