利用喇曼光谱测量氧碘化学激光器氯气利用率的实验研究

 介绍了利用自发喇曼散射光谱测量氧碘化学激光器单态氧发生器氯气利用率的原理及实验装置，并给出了在以氮气作为稀释气的0.1mol/s射流式氧发生器上测试的结果，测试相对误差小于12%。由于该方法只需要通过测量喇曼谱线相对强度之比，即可算出氯的利用率，因此不需要另外的标定实验，从而避免了因标定带来的影响。该方法减小了测试误差，简化了实验过程，提高了测试效率。     

Inelastic light scattering by collective excitations in the fractional quantum Hall regime

We report an inelastic light scattering study of long wavelength collective gap excitations of fractional quantum Hall (FQH) states at ν=p/(2p+1) for . The ν-dependence of the gap energy suggests a collapse of the collective excitation gap near . In a range of filling factors close to , where the FQH gap is believed to collapse, we observe a collective excitation mode that exists only at temperatures below 150 mK.     

976 nm激光抽运二氧化硅微球级联拉曼散射激光的研究

利用电极放电产生的电弧高温熔融二氧化硅单锥细纤, 熔融的二氧化硅在表面张力作用下形成表面光滑的微球, 完成高品质因子微球腔的制备. 将976 nm激光通过锥光纤以倏逝场方式高效耦合入微球, 研究具有高能量密度回廊模的微球腔中的三阶非线性现象——受激拉曼散射现象. 在实验中测得了六级级联的拉曼散射激光, 各级拉曼散射激光分别测得单纵模或多纵模; 在抽运光功率不少于582.6 μW时, 测得位于1200 nm附近的拉曼散射激光; 当抽运光功率为3.014 mW时, 测得位于1287.04 nm附近的第六级拉曼散射激光. 关键词： 微球腔 锥光纤 高品质因子 拉曼散射激光     

基于增强拉曼散射的光子-原子双模压缩态的实现

拉曼散射过程中利用原子系综中初始制备的自旋激发(原子相干性),以及注入与原子系综中初始制备的自旋激发相关联的种子光场都可以极大的提高光场频率转换的效率,实现增强拉曼散射.本文理论上计算了增强拉曼散射过程中原子-光场量子界面的正交分量的量子起伏,得到了相干性导致的增强拉曼散射,只能在一定的范围内稍微提高初始光子-原子的压缩度;而关联增强拉曼散射,能够制备很强的光子-原子间的双模压缩.这样强压缩度的光子-原子量子界面,对于利用光场和原子系统实现量子精密测量研究有着非常重要的应用.     

分子极性对类胡萝卜素共振拉曼光谱的影响

测量了非极性分子β胡萝卜素和极性分子角黄素, 在非极性溶剂CS₂和极性溶 剂1,2二氯乙烷中243–293 K的温度范围内的共振拉曼光谱. 结果表明, 溶质和溶剂的极性对拉曼光谱影响很大. 非极性分子β胡萝卜素在非极性溶剂CS₂中的拉曼散射截面最大, 线宽最窄, 而极性分子角黄素在极性溶剂1,2二氯乙烷中的拉曼散射截面最小, 线宽最大. 用溶剂效应及线性多烯分子的“相干弱阻尼电子-晶格振动”, “有效共轭长度”模型给予了解释.     

Theory of two-phonon modes in layered charge-density-wave systems

A theoretical model with electron-phonon and anharmonic interactions is proposed to explain the two-phonon mode observed in the Raman spectra of layered transition metal dichalcogenides, which exhibit charge density wave (cdw) phase transition. The phonon self-energy, which involves the electron response function and the two-phonon Green’s function, is calculated using the double-time Green’s function formalism. It is shown that in these low-dimensional systems there exists an anharmonicity-mediated two-phonon mode in the phonon spectral function both in the normal and in thecdw phases. In the normal phase since the phonon Raman scattering proceeds through a single optic phonon the calculations are carried out for zero wave vector and hence the contribution of the electron response function to the self-energy vanishes. On the other hand explicit evaluation of the two-phonon Green’s function shows that the frequency of the two-phonon mode is twice that of the Kohn anomaly phonon and decreases with decreasing temperature. The strength of two-phonon peak is found to be comparable to that of the original optic phonon. In thecdw phase the phonon which enters into the Raman scattering is taken to be the one with thecdw wave vectorQ, which when zone-folded becomes equivalent to zero wave vector. The evaluation of the electron response function in this phase generates a phonon corresponding to thecdw-amplitude mode. The two-phonon Green’s function is assumed to be of similar form as in the normal phase. The spectral function evaluated at zero temperature shows a weak two-phonon peak besides the prominentcdw-amplitude mode. Numerical results are presented for the system 2H-NbSe₂ and are found to be in qualitative agreement with the experimental data.     

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应用多光子非线性Compton散射模型和时域有限差分法,对Compton散射对时变非磁化等离子体光子晶体禁带的影响进行了研究,提出了将多光子非线性Compton散射电磁波和入射电磁波作为等离子体光子晶体产生光子禁带的新机制,给出了电磁场的Maxwell方程组和叠代方程的修正方程,并进行了数值模拟。结果表明,Compton散射使等离子体禁带宽随等离子体上升时间的增大比散射前有明显减小而最后趋于定值,均匀等离子体透射率峰值比线性等离子体增大得更多,利用Compton散射可实现对光子禁带的控制。     

激光等离子体受激Raman散射光谱的时间分辨测量

采用光学多道谱仪和光学条纹相机耦合,组成时间分辨的Raman散射光谱测量系统,可实现0.5nm的光谱分辨和好于10ps的时间分辨。采用该测量系统,在神光Ⅱ装置上开展了脉宽1ns、波长351nm的激光与两种不同尺寸柱腔靶相互作用的物理实验,获得了时间分辨的SRS光谱实验结果。研究表明,SRS光谱在时间上相对于入射激光有一定的延迟,腔靶尺寸减小时,延迟时间随之减小。通过长、短波截止波长分析电子密度方法,计算得出了Ⅰ型和Ⅱ型腔靶SRS散射光最短波长光谱发生的密度区分别为0.069nc和0.027nc。     

The role of CDW gap on the magnetic phase transition in CMR materials

We propose a model to study the magnetic phase transition in the Colossal-Magneto-Resistance (CMR) material of general type R_1−x A _x MnO₃ (R = La, Sm, Nd; A = Ca, Sr, Ba). The model Hamiltonian consists of a Charge Density Wave (CDW) gap in the e _g -band and the strong magnetic field due to the spin ordering in the localized t _g core electrons. The Hamiltonian is solved by using Zubarev’s Green’s function technique to calculate CDW gap (Δ) and magnetization (M ^d ) in t _2g band. Both of them are solved self-consistently. Their combined effect on the temperature dependent magnetization (M ^c ) due to the e _g band electrons is investigated. Both the magnitude and the transition temperature of (M ^c ) are strongly influenced by both Δ and M ^d . Hence the hopping of the band electrons are strongly controlled by these two long range interactions. The results are discussed by varying the model parameters of the manganite system.      

Vibronic scheme of the franck-condon state of F centers that consistently elucidates MCD and resonance raman scattering

Abstract

The resonance Raman scattering (RRS) of F centers, particularly the photon-energy dependence of linear polarization of the RRS, has been studied on the basis of a vibronic viewpoint. With combinination of previous results that have explained magnetic circular dichroism (MCD) spectra, a vibronic scheme of the Franck-Condon state of F centers for KCl, KBr and KI crystals is established.     

Selective excitation and suppression of coherent anti-Stokes Raman scattering by shaping femtosecond pulses

Femtosecond coherent anti-Stokes Raman scattering (CARS) suffers from poor selectivity between neighbouring Raman levels due to the large bandwidth of the femtosecond pulses. This paper provides a new method to realize the selective excitation and suppression of femtosecond CARS by manipulating both the probe and pump (or Stokes) spectra. These theoretical results indicate that the CARS signals between neighbouring Raman levels are differentiated from their indistinguishable femtosecond CARS spectra by tailoring the probe spectrum, and then their selective excitation and suppression can be realized by supplementally manipulating the pump (or Stokes) spectrum with the $\pi $ spectral phase step.     

Nd:YAG四倍频激光抽运甲烷后的受激拉曼效应及其物理机制分析

从理论上分析了激光被聚焦到高压气体内可能发生各种非线性现象的规律及其相互作用和相互干扰.在实验中把Nd:YAG四倍频激光聚焦到充有甲烷的拉曼管内,测各阶斯特克斯光输出能量与气压pa、透镜焦距f和输入能量Ep之间的关系.实验结果与理论分析定性地相符合，这就为我们优化和利用受激拉曼过程提供了理论和实验依据. 关键词： 非线性过程 受激拉曼散射 四波混频 激光诱导离解     

用变温霍尔效应估测锑化铟的禁带宽度

通过变温霍尔效应实验获得锑化铟的霍尔系数随温度变化的数据,根据半导体的霍尔系数随温度的变化规律,计算出禁带宽度,并且着重讨论禁带宽度的两种求法,比较了两种方法的计算精度.     

Effect of a fluorescing impurity on the characteristics of stimulated Raman scattering from acetone

Asymmetry in the intensities between backward and forward stimulated Raman scattered radiations (BSRS and FSRS respectively) in acetone is investigated in the presence of a fluorescing impurity (rhodamine 6G). In the case of pure acetone above a threshold pump power, BSRS becomes more intense than FSRS. On the other hand intensity of BSRS decreases with concentration of the fluorophore in solution, while that of FSRS is found to increase. It is observed that absorption saturation also affects the asymmetry between FSRS and BSRS.     

Effect of 6H-SiC （1120） substrate on epitaxial graphene revealed by Raman scattering

A nonpolar SiC(1120) substrate has been used to fabricate epitaxial graphene (EG). Two EGs with layer numbers of 8-10 (referred to as MLG) and 2-3 (referred to as FLG) were used as representative to study the substrate effect on EG through temperature dependent Raman scattering. It is found that Raman lineshifts of G and 2D peaks of the MLG with temperature are consistent with that of a free graphene predicted by theory calculation, indicating that the substrate influence on the MLG is undetectable. While Raman G peak lineshifts of the FLG to that of the free graphene are obvious, however, its lineshift rate (-0.016 cm^-1/K) is almost one third of that (-0.043 cm^-1/K) of a EG on 6H-SiC (0001) in the temperature range from 300 K to 400 K, indicating a weak substrate effect from SiC (1120) on the FLG. This renders the FLG a high mobility around 1812 cm²- ·V^-1-·s^-1 at room temperature even with a very high carrier concentration about 2.95× 10¹³ cm^-2 (p-type). These suggest SiC (1120) is more suitable for fabricating EG with high performance.     

Effect of spontaneous Raman scattering on quantum channel wavelength-multiplexed with classical channel

We quantitatively estimate the effect of spontaneous Raman scattering on a quantum channel wavelength-multiplexed with a classical channel. Based on an experiment that measured the generation power of spontaneous Raman scattering in a fiber, the performance of wavelength-multiplexed quantum key distribution (QKD) systems using the differential-phase-shift protocol is evaluated for various system conditions.