High-resolution Infrared Spectroscopy of ^15N2^16O in 1650-3450 cm-1

High-resolution ro-vibrational spectroscopy of ^15N2^16O in 1650-3450 cm-1 region is studied using highly enriched isotopologue sample. The positions of more than 7300 lines of ^15N2^16O isotopologue were measured with a typical accuracy of 5.0×10-4 cm-1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian model. The band by band analysis allowed for the determination of the rovibrational parameters of a total of 73 bands. 29 of them are newly reported and more rotational transitions have been observed for the others. The maximum deviation of the preidictions of the effective Hamiltonian model is up to 0.70 cm-1 for the ^15N2^16O species.

High-Resolution Rb Two-Photon Transition Spectroscopy by a Femtosecond Frequency Comb via Pulses Control

We experimentally observe the high resolution direct frequency comb spectroscopy using counter-propagating broadband femtosecond pulses on two-photon transitions in room-temperature ^87 Rb atoms. The Doppler broad- ened background is effectively eliminated with the pulse shaping method and the spectrum modulation technique. The combination of the pulse shaping method and the spectra modulation technique provides a potential approachto reduce background of at least 99%.

High-Resolution Mass Spectroscopy for Revealing the Charge Storage Mechanism in Batteries: Oxamide Materials as an Example

The pursuit of high-performance electrode materials is highly desired to meet the demand of batteries with high energy and power density.However,a deep understanding of the charge storage mechanism is always challenging,which limits the development of advanced electrode materials.Herein,high-resolution mass spectroscopy(HR-MS)is employed to detect the evolution of organic electrode materials during the redox process and reveal the charge storage mechanism,by using small molecular oxamides as an example,which have ortho-carbonyls and are therefore potential electrochemical active materials for batteries.The HR-MS results adequately proved that the oxamides could reversibly store lithium ions in the voltage window of 1.5–3.8 V.Upon deeper reduction,the oxamides would decompose due to the cleavage of the C–N bonds in oxamide structures,which could be proved by the fragments detected by HR-MS,^(1)H NMR,and the generation of NH_(3)after the reduction of oxamide by Li.This work provides a strategy to deeply understand the charge storage mechanism of organic electrode materials and will stimulate the further development of characterization techniques to reveal the charge storage mechanism for developing high-performance electrode materials.

Large Amplitude Motion in 9-Methylanthracene:High-Resolution Spectroscopy and Ab Initio Theoretical Calculation

CH3 internal rotation is one of the typical large amplitude motions in polyatomic molecules,the spectral analysis and theoretical calculations of which,were developed by Li-Hong Xu and Jon Hougen.We observed a Doppler-free high-resolution and high-precision spectrum of 9-methylanthracene(9MA)by using the collimated supersonic jet and optical frequency comb techniques.The potential energy curve of CH3 internal rotation is expressed by a six-fold symmetric sinusoidal function.It was previously shown that the barrier height(V6)of 9MA-d12 was considerably smaller than that of 9MA-h12[M.Baba,et al.,J.Phys.Chem.A 113,2366(2009)].We performed ab initio theoretical calculations of the multicomponent molecular orbital method.The barrier reduction by deuterium substitution was partly attributed to the difference between the wave functions of H and D atomic nuclei.

Coherent Vibrational Dynamics and High-resolution Nonlinear Spectroscopy： A Comparison with the Air/DMSO Liquid Interface

We present a comparative study on the C-H stretching vibrations at air/DMSO （dimethyl sulfoxide） interface with both the free-induction decay （FID） coherent vibrational dynamics and the sub-wavenumber high resolution sum-frequency generation vibrational spectroscopy measurements. In principle the frequency-domain and time-domain spectroscopic measurements should generate identical information for a given molecular system. However, when the molecular systems are with several coupled or overlapping vibrational modes, obtain- ing detailed spectroscopic and coherent dynamics information is not as straightforward and rather difficult from either the time-domain or the frequency domain measurements. For the case of air/DMSO interface that is with moderately complex vibrational spectra, we show that the frequency-domain measurement with sub-wavenumber high-resolution sum-frequency generation vibrational spectroscopy is probably more advantageous than the time- domain measurement in obtaining quantitative understanding of the structure and coherent dynamics of the molecular interface.

Evidence of Electron-Hole Imbalance in WTe2 from High-Resolution Angle-Resolved Photoemission Spectroscopy

WTe2 has attracted a great deal of attention because it exhibits extremely large and non-saturating magnetore- sistance. The underlying origin of such a giant magnetoresistance is still under debate. Utilizing laser-based angle-resolved photoemission spectroscopy with high energy and momentum resolutions, we reveal the complete electronic structure of WTe2. This makes it possible to determine accurately the electron and hole concentrations and their temperature dependence. We find that, with increasing the temperature, the overall electron concen- tration increases while the total hole concentration decreases. It indicates that the electron-hole compensation, if it exists, can only occur in a narrow temperature range,and in most of the temperature range there is an electron-hole imbalance. Our results are not consistent with the perfect electron-hole compensation picture that is commonly considered to be the cause of the unusual magnetoresistance in WTe2. We identify a fiat band near the Brillouin zone center that is close to the Fermi level and exhibits a pronounced temperature dependence. Such a fiat band can play an important role in dictating the transport properties of WTe2. Our results provide new insight on understanding the origin of the unusual magnetoresistance in WTe2.

Terahertz radiation of a butterfly-shaped photoconductive antenna(invited)

The terahertz(THz) far-field radiation properties of a butterfly-shaped photoconductive antenna(PCA) were experimentally studied using a home-built THz time-domain spectroscopy(THz-TDS) setup.To distinguish the contribution of in-gap photocurrent and antenna structure to far-field radiation,polarization-dependent THz field was measured and quantified as the illuminating laser beam moved along the bias field within the gap region of electrodes. The result suggests that, although the far-field THz radiation originates from the in-gap photocurrent, the antenna structure of butterfly-shaped PCA dominates the overall THz radiation. In addition, to explore the impact of photoconductive material,radiation properties of butterfly-shaped PCAs fabricated on both low-temperature-grown GaAs(LT-GaAs) and semi-insulating GaAs(Si-GaAs) were characterized and compared. Consistent with previous experiments, it is observed that while Si-GaAs-based PCA can emit higher THz field than LT-GaAs-based PCA at low laser power, it would saturate more severely as laser power increased and eventually be surpassed by LT-GaAs-based PCA. Beyond that, it is found the severe saturation effect of Si-GaAs was due to the longer carrier lifetime and higher carrier mobility, which was confirmed by the numerical simulation.

A new nonlinear photoconductive terahertz radiation source based on photon-activated charge domain quenched mode

We present a high-performance terahertz(THz)radiation source based on the photon-activated charge domain(PACD)quenched mode of GaAs photoconductive antennas(GaAs PCA).The THz radiation characteristics of the GaAs PCA under different operating modes are studied.Compared with the linear mode,the intensity of THz wave radiated by the GaAs PCA can be greatly enhanced due to the avalanche multiplication effect of carriers in the PACD quenched mode.The results show that when the carrier multiplication ratio is 16.92,the peak-to-peak value of THz field radiated in the PACD quenched mode increases by as much as about 4.19 times compared to the maximum values in the linear mode.

<i>In-Situ</i>Measurements of the Photoconductivity of Multi-Layered Organic Photovoltaic Devices Using Impedance Spectroscopy

In-situ impedance spectroscopy (IS) observations of the photoconductivity of the carriers induced by photo-irradiation in organic hetero-junction structured photovoltaic devices are presented. In the IS measurements, the externally applied voltage and the dependence of the light intensity applied to the device were investigated. Analysis of the frequency characteristics which was measured by changing the light intensity shows there is a proportional relationship between the changes in the conductivities of the two components. The mobilities of the CuPc and C60 layers were calculated from the conductivities and were in the orders of 10﹣4 and 10﹣3 cm2/Vs, respectively.

Metabonomic studies of pancreatic cancer response to radiotherapy in a mouse xenograft model using magnetic resonance spectroscopy and principal components analysis

AIM: To investigate the metabolic profiles of xenograft pancreatic cancer before and after radiotherapy by high-resolution magic angle spinning proton magnetic resonance spectroscopy (HRMAS 1H NMR) combined with principal components analysis (PCA) and evaluate the radiotherapeutic effect. METHODS: The nude mouse xenograft model of human pancreatic cancer was established by injecting human pancreatic cancer cell SW1990 subcutaneously into the nude mice. When the tumors volume reached 800 mm3 , the mice received various radiation doses. Two weeks later, tumor tissue sections were prepared for running the NMR measurements. 1H NMR and PCA were used to determine the changes in the metabolic profiles of tumor tissues after radiotherapy. Metabolic profiles of normal pancreas, pancreatic tumor tissues, and radiationtreated pancreatic tumor tissues were compared. RESULTS: Compared with 1H NMR spectra of the normal nude mouse pancreas, the levels of choline, taurine, alanine, isoleucine, leucine, valine, lactate, and glutamic acid of the pancreatic cancer group were increased, whereas an opposite trend for phosphocholine, glycerophosphocholine, and betaine was observed. The ratio of phosphocholine to creatine, and glycerophosphocholine to creatine showed noticeable decrease in the pancreatic cancer group. After further evaluation of the tissue metabolic profile after treatment with three different radiation doses, no significant change in metabolites was observed in the 1H NMR spectra, while the inhibition of tumor growth was in proportion to the radiation doses. However, PCA results showed that the levels of choline and betaine were decreased with the increased radiation dose, and conversely, the level of acetic acid was dramatically increased. CONCLUSION: The combined methods were demonstrated to have the potential for allowing early diagnosis and assessment of pancreatic cancer response to radiotherapy.

Highly sensitive photoassociation spectroscopy of ultracold 23Na133Cs molecular long-range states below the 3S1/2＋6P3/2 limit

We present high resolution photoassociation spectroscopy of ultracold 23Na133Cs molecules in a long-range c3∑＋ state below the （3S1/2 ＋ 6P3/2） asymptote. We perform photoassociation spectroscopy in a dual-species magneto-optical trap （MOT） and detect the photoassociation resonances using trap-loss spectroscopy. By fitting the experimental data with the semi-classical LeRoy-Bernstein formula, we deduce the long-range molecular coefficient C6 and derive the empirical potential energy curve in the long-range region.

全光纤耦合式太赫兹近场探针光谱成像系统

通过对太赫兹光电导探针天线与飞秒倍频光路进行光纤模块化封装,并结合光纤耦合式太赫兹光电导天线辐射源,以及自主研制设计的光纤飞秒激光光源和光纤式高速光学延时线,开发了一种全光纤耦合式太赫兹近场探针光谱成像系统,其光谱范围覆盖0.1~2.0 THz,动态范围达到60 dB,光谱采样速度高达0.1 s/谱,近场成像分辨率优于20μm的全光纤耦合式太赫兹近场探针光谱成像系统。得益于整套系统的全光纤结构设计,太赫兹辐射源和探针式探测器之间可以根据测量需求灵活调节而不需要重新校准光路,极大地提高了系统的工作稳定性和使用方便性。该研究为太赫兹科学研究提供了一种高性能且实用性强的太赫兹近场光谱成像测量系统。

In_(0.52)Al_(0.48)As/InP的正向和反向异质结在带隙附近的不同光谱现象

应用光电导谱(PC)和光致发光谱(PL)研究了由分子束外延在InP(100)衬底上生长In_(0.52)Al_(0.48)As获得的两种异质结外延结构,分别是在InP衬底上生长InAlAs形成的正向异质结样品(样品A:In_(0.52)Al_(0.48)As/InP)和InAlAs层继续生长InP形成的上层为反向异质结的双异质结样品(样品B:InP/In_(0.52)Al_(0.48)As/InP).PL和PC实验采用光从表面入射激发的测量构型,样品测量温度为77 K.样品A的PC谱显示,在激发光能量大于表面In_(0.52)Al_(0.48)As层的带隙时出现了电导陡降的反常变化,还在916 nm波长处呈现一小的电导峰结构.PL谱对应此波长位置则出现很强的发光峰.样品B则未观察到上述光谱特征,该差异可从两类异质结不同的界面电子结构获得解释.

Grade classification of neuroepithelial tumors using high-resolution magic-angle spinning proton nuclear magnetic resonance spectroscopy and pattern recognition

Clinical data have shown that survival rates vary considerably among brain tumor patients,according to the type and grade of the tumor.Metabolite profiles of intact tumor tissues measured with high-resolution magic-angle spinning proton nuclear magnetic resonance spectroscopy (HRMAS 1H NMRS) can provide important information on tumor biology and metabolism.These metabolic fingerprints can then be used for tumor classification and grading,with great potential value for tumor diagnosis.We studied the metabolic characteristics of 30 neuroepithelial tumor biopsies,including two astrocytomas (grade I),12 astrocytomas (grade II),eight anaplastic astrocytomas (grade III),three glioblastomas (grade IV) and five medulloblastomas (grade IV) from 30 patients using HRMAS 1H NMRS.The results were correlated with pathological features using multivariate data analysis,including principal component analysis (PCA).There were significant differences in the levels of N-acetyl-aspartate (NAA),creatine,myo-inositol,glycine and lactate between tumors of different grades (P<0.05).There were also significant differences in the ratios of NAA/creatine,lactate/creatine,myo-inositol/creatine,glycine/creatine,scyllo-inositol/creatine and alanine/creatine (P<0.05).A soft independent modeling of class analogy model produced a predictive accuracy of 87% for high-grade (grade III-IV) brain tumors with a sensitivity of 87% and a specificity of 93%.HRMAS 1H NMR spectroscopy in conjunction with pattern recognition thus provides a potentially useful tool for the rapid and accurate classification of human brain tumor grades.

Photoconductive devices for terahertz pulsed spectroscopy:a review[Invited]

Photoconductive switches were the key components that allowed the generation and detection of coherent broadband electromagnetic pulses at terahertz frequencies, opening the possibility for performing spectroscopy and,therefore, measuring complex dielectric properties of materials in this band, which was mostly unexplored. In this paper, we present a brief introduction to the operation principles of these devices. Subsequently, we present a review of the current state-of-the-art in this field and discuss the challenges to be faced in future development of these devices.

Ordering effects of cholesterol on sphingomyelin monolayers investigated by high-resolution broadband sum-frequency generation vibrational spectroscopy

This report investigated the ordering of the alky chain of sphingomyelin （SMs） monolayers induced by cholesterol at the air/water interface using high-resolution broadband sum frequency generation vibrational spectroscopy （HR-BB-SFG-VS）. The SFG spectra of the three nature sphingomyelin/cholesterol mixture monolayers with two concentrations of the cholesterol at the air/water interface are performed under different polarization combination. A new resolved CH2 symmetric stretching （d＋, ~2834 cm-1） and the CH3 symmetric stretching （r＋, ~2874 cm-1） mode are applied to characterize the conformational order in the sphingomyelin/cholesterol mixture monolayers. It was found that the cholesterol make the sphingosine backbones more conformational order. During this process, the conformational order of the N-linked acyl chain remains unaltered. Moreover, the sphingosine backbones of SMs have much larger contributions to gauche defects of SMs than one in the N-linked acyl chain. These results presented here not only shed lights on understanding of the interactions of sphingomyelin molecules with cholesterol molecules at interface but also demonstrates the ability of HR-BB-SFG to probe such complicated molecular systems.

基于光导开关脉冲偏置电压的太赫兹时域光谱系统

利用光导开关产生脉冲偏置电压的方式改进了基于光电导天线的太赫兹时域光谱系统。在分析光电导天线产生THz波原理的基础上,重点研究了目前基于光电导天线的太赫兹时域光谱系统存在的问题,探讨了解决斩波器引起的机械噪声和光电导天线脉冲偏置电压之间矛盾的途径。最后,通过对光导开关的特性测试,提出了利用高压直流电源、光导开关和纳秒激光器产生0～9kV脉冲偏置电压消除机械噪声、提高脉冲偏置电压幅度的方法,改进了太赫兹时域光谱系统。

基于飞秒激光的超快太赫兹特征波谱技术及其应用(特邀)

太赫兹特征波谱技术作为一种太赫兹波段的相干测量技术,具有高灵敏、快速、无损检测等显著特点,可以有效获得来源于物质分子的低频集体振动、转动模式以及与周围分子的弱相互作用(氢键、范德华力等)而产生的特征“指纹谱”信息,已在生化分子检测、材料分析与辨识等方面展现出非常广阔的应用前景。太赫兹光电导天线作为一类应用广泛的太赫兹波源,能够产生宽频带的太赫兹辐射,由其构成的超快太赫兹特征波谱系统在生化分子和材料分析等方面已显现重要应用。本文首先介绍了基于超短脉冲激光的太赫兹光电导天线的工作原理及其发展现状,包括理论模型、衬底材料以及不同结构形式。随后,介绍了由太赫兹光电导天线作为宽频带太赫兹波源而构建的超快太赫兹特征波谱系统及其工作机理,详细阐述了基于飞秒激光的超快太赫兹特征波谱技术及其应用取得的一些最新研究进展,并分析讨论了该技术在实际应用过程中面临的挑战和应对策略。

不同光功率激励下石墨烯的太赫兹波吸收特性（英文）

基于太赫兹时域光谱系统和德鲁德模型,测量并分析了少层石墨烯在600nm CW红光和两种衬底下的透过率及电导率.结果发现,高阻硅衬底的石墨烯样品在光场激励下对太赫兹信号的吸收显著增强,而PET(Polyethylene terephthalate)衬底的石墨烯样品在光场激励下对太赫兹信号的吸收则有微弱减少.相较于无激励光场条件,在0.5THz处,高阻硅衬底石墨烯的电导率提升了7倍,PET衬底石墨烯的电导率下降了23%.同时实验也验证了在太赫兹波段少层石墨烯的电导为各层石墨烯电导的线性叠加.

CuPc/ZnS多层复合薄膜的制备及光电性能的研究

为了找到制备具有最佳光电导性能的CuPc/ZnS多层复合薄膜的工艺参数 ,研究了CuPc/ZnS多层复合膜的层数系列、CuPc膜层的厚度系列、ZnS膜层的厚度系列和基板温度系列的光电导性能和结构。利用表面电位衰减、紫外 可见光谱和X射线衍射分析了复合薄膜的光电导性能和结构及其关系 ,探讨了改变复合膜层数。