高压H_2的SRS中的参量与非参量过程

本文报道了在数十气压H_2中输出三级Stokes和六级anti-Stokes受激喇曼散射。着重研究了SRS能量转移中的受激喇曼过程(SRP)和四波参量过程(FWPP)。对前人报道得很少的高压H_2中的离轴Stokes圆环与轴上anti-Stokes圆斑进行了较系统的实验研究,并用非线性光学参量与非参量过程的有关理论对实验结果进行了讨论。     

高压H2的SRS中的参量与非参量过程

本文报道了在数十气压H₂中输出三级Stokes和六级anti-Stokes受激喇曼散射。着重研究了SRS能量转移中的受激喇曼过程(SRP)和四波参量过程(FWPP)。对前人报道得很少的高压H₂中的离轴Stokes圆环与轴上anti-Stokes圆斑进行了较系统的实验研究,并用非线性光学参量与非参量过程的有关理论对实验结果进行了讨论。 关键词：     

磁场中的拓扑绝缘体边缘态性质

用数值方法研究了拓扑绝缘体薄膜体系在外加垂直磁场 作用下其边缘态的性质. 磁场的加入通过耦合k+eA, 即Peierls势替换关系和 该作用导致的Zeeman交换场体现在哈密顿量中. 考虑窄条圆环状结构的二维InAs/GaSb/AlSb薄膜量子阱材料, 当其处于拓扑非平庸状态, 即量子自旋霍尔态时, 会出现受时间反演对称性保护的两支简并边缘态, 而在垂直磁场的作用下, 时间反演对称性被破坏, 这时能带将形成一条条的朗道能级, 原来简并的两支边缘态也会分开到朗道能级谱线的两侧, 从电子态密度的空间分布情况则可以看到边缘态分别局域在材料的两个边界. 随着磁场的增大, 位于同一边界上的不同 自旋极化的边缘态将出现分离: 一支仍然局域在边缘, 另一支则随外加磁场的增加而有逐渐演化到材料内部的趋势. 文中还计算了同一边界上的两支边缘态之间的散射, 结果表明由于两个边缘态在空间发生分离, 相互之间的散射被很大的压制, 得到了其散射随磁场增加没有明显变化的结论, 所以磁场并不会增强散射过程, 也没有破坏体拓扑材料的性质, 说明了量子自旋霍尔态在没有时间反演对称的情况下也可以有较强的稳定性.     

d波超导体NIS结中的时间反演对称态的破缺与准粒子寿命效应

考虑到d波超导表面时间反演对称态的破缺与准粒子的有限寿命效应,在BlonderTinkhamKlapwijk(BTK)理论框架下,通过求解BogoliubovdeGennes(BdG)方程,计算正常金属d波超导隧道结中的准粒子输运系数与隧道谱.研究表明:1)d波超导表面时间反演对称态的破缺会导致零偏压电导峰位移,位移的程度取决于分解d波超导表面时间反演对称态中s波分量的强度;2)准粒子的寿命效应与粗糙界面散射效应都能压低零偏压电导峰,其中粗糙界面散射还会阻碍零偏压电导峰的位移.这些结果能较好地解释Tc氧化 关键词：     

多色宽带相干反斯托克斯拉曼散射过程的理论与实验研究

宽带相干反斯托克斯拉曼散射(coherent anti-Stokes Raman scattering,CARS)光谱技术能够同时获取完整的分子CARS光谱信息,以准确识别和定量分析混合物中的不同成分或未知成分.在宽带CARS光谱技术中,由于超连续谱激光有效光谱范围内各光谱成分的作用不同,分别会产生双色和三色CARS过程.这里我们在理论上分析了宽带激发条件下两种CARS过程的产生条件,以及不同CARS光谱信号强度与各激发光功率之间的关系.在此基础上,搭建了基于SC激光的宽带CARS光谱系统,分别实现了双色和三色CARS过程.通过对获得的苯甲腈样品的CARS光谱信号进行函数拟合分析,实验验证了上述两个过程中CARS信号的强度与各激发光强度之间的函数关系.理论和实验研究结果为进一步优化宽带时间分辨CARS光谱探测和显微系统,实现同时获取物质分子完整的CARS光谱信号提供了指导.     

Non-classical correlation between a single photon and the collective spin excited state of a cold atomic ensemble

We experimentally establish a non-classical correlation between a single Stokes photon and the collective spin excited state of a cold atomic ensemble by using a spontaneous Raman scattering process. The correlation between them can be proved by transferring the spin excited state of the atomic ensemble into an anti-Stokes photon and checking the Cauchy-Schwarz inequality between the Stokes and the anti-Stokes photons. The non-classical correlation can be kept for at least 300 ns.     

冷原子系综中偏振关联光子对的产生和测量

我们在~(87)Rb冷原子系综中进行了关联光子对的产生和测量。通过自发拉曼散射过程,产生了一个Stokes光子和一个原子自旋波激发。利用电磁感应透明效应将存储在原子系综中的自旋波转化为一个anti-Stokes光子。在两相互正交的偏振基下,测量了Stokes光子和anti-Stokes光子之间的交叉关联函数。实验结果表明,交叉关联函数g~(2)达到~75,表现了强的非经典关联。基于现场可编程门阵列(FPGA)的自编程的多通道符合器被用于光子脉冲信号的采集和逻辑处理,大大提高了偏振关联光子对的产生和测量速度,为以后量子中继技术中的高效信息处理提供了重要基础。     

非简并拉曼过程中交流斯塔克位移对腔场谱的影响

研究了原子与双模光场非简并拉曼耦合过程中交流斯塔克位移对腔场谱的影响.给出了原子处于基态且双模初始场为光子数态、相干态和压缩真空态时光谱结构的数值结果.发现数态光场在弱场条件下每模腔场谱都是三峰结构，在强场条件下则为双峰或单峰结构，相干态和压缩真空态光场的腔场谱在弱场或强场条件下都是双峰结构.随着斯塔克位移参数的变化,双峰的高度此长彼消. 关键词： 交流斯塔克位移 非简并拉曼过程 腔场谱     

考虑地表反射类型的气溶胶散射偏振特性

采用逐次阶散射法求解矢量辐射传输方程来研究气溶胶在不同地表反射模型下的散射偏振特性.首先,选取单一地表反射模型和耦合地表反射模型两种地表反射模型.然后,根据地表反射模型计算得到相应的地表反射率,进而采用逐次阶散射法对矢量辐射传输方程进行求解,得到散射光的Stokes矢量.最后,由Stokes矢量计算得出散射光的偏振度.仿真结果表明,两种地表反射模型下气溶胶单次散射的散射辐射强度和线偏振度均相等;耦合地表反射模型的总散射辐射强度和线偏振度总是大于单一地表反射模型;单一地表反射模型的气溶胶单次散射相对总散射的贡献总是大于耦合地表反射模型.研究结果对气溶胶光学特性的反演具有一定意义.     

原子受激态的Stokes参数分析

根据密度矩阵理论，导出了受激原子态P态密度矩阵元和P态退激辐射的光子密度矩阵元的Stokes参数，它们之间存在一种非常简单直接的关系，说明在电子-光子符合散射实验中，通过测量光子的Stokes参数，就可以描述受激P态电荷云分布和散射过程的动力学。According to the density matrix theory, the density matrix of photon emitted from excited atom P state and of P state were introdued in this paper. There were a simple direct relation between the two density matrices, which shows that the electron cloud shape of excited atomic state and scattering dynamics can be described through the observable Stokes parameters of photon in electron-photon coincidence experiment.     

Tunable coherent radiation source covering a spectral range from 185 to 880 nm

We have studied experimentally stimulated Raman scattering and 4-wave-interaction processes occuring in hydrogen gas, which is excited by a Nd:YAG-pumped dye laser. The tuning ranges of the various Stokes and anti-Stokes lines, which are generated with high efficiency, cover the spectrum from 185 to 880 nm without a gap.     

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.     

强激光照射下,α-LiIO3晶体中晶格振动的多模激发和模之间的相互作用

本文叙述了用调Q倍频YAG脉冲激光照射α-LiIO₃晶体,在不同的散射配置下,获得了各种散射谱图。实验表明,当用e光入射时,可以比用o光入射激发起更多不同模的晶格振动;获得了E₂模的很强的一阶、二阶斯托克斯散射线和反斯托克斯散射线,E₁模Polariton的一阶、二阶、三阶斯托克斯线和反斯托克斯线,还获得了反斯托克斯频率区一条频移为469cm^-1的新线,认为是不同模的Polariton之间的相互作用引起的。最后,提到实验中初步观察到的晶体拉曼活性的“疲劳现象”。 关键词：     

Coherent anti-Stokes resonance Raman scattering of excited molecules

A theoretical investigation of the coherent anti-Stokes resonance Raman scattering (CARRS) of excited molecules is given. The calculation of the anti-Stokes intensity predicts the simultaneous appearance of the vibrational frequencies of the ground and the excited electronic state in the CARRS spectra. The line shape of these spectra and the optimum conditions for the anti-Stokes amplification are discussed.     

On stability of Raman and degenerate hyper-Raman scattering

The problem of the stationary generation by Raman and degenerate hyper-Raman scattering is solved by means of two methods: stationary solution of the generalized Fokker-Planck equation and linear analysis of stability of the Langevin equations. The conditions of stability and the corresponding stationary values for amplitudes of the Stokes, anti-Stokes or output laser modes are obtained for particular cases. A phenomenon analogous to the second order phase transition can occur for Stokes or anti-Stokes interaction of Raman scattering above the threshold value of the pump amplitude. The anti-Stokes interaction of degenerate hyper-Raman scattering can show bistable behaviour above the second threshold value of the pump amplitude.The author would like to express his sincere thanks to Dr. J. Peina for comments and stimulating discussions.     

水的低频受激拉曼散射

利用532 nm的脉冲激光进行了水的受激拉曼散射研究. 水的低激发光能量下主要表现为受激Stocks和反Stocks 3426 cm^-1谱线; 在能量大于140 mJ时出现低频率313 cm^-1受激Stocks谱线, 同时出现后向3389和3268 cm^-1 的受激Stocks谱线. 实验结果表明, 在较强的激光作用下, 水的结构表现为冰的Ⅷ相.     

Double resonance Raman scattering of second-order Raman modes from an individual graphite whisker

Resonant Raman scattering of second-order Raman modes from an individual graphite whisker synthesized by a high-temperature heat-treatment method at a special pressure was discussed here. The dependence of phonon frequencies on the incoming laser light and the frequency difference between Stokes and anti-Stokes scattering show their origin from double resonance Raman scattering. Our results show that all the experimental results of second-order Raman modes in graphite whiskers, such as the excitation-energy dependence on the mode frequency, the frequency shift between a second-order Raman mode and its fundamentals, and the frequency discrepancy between Stokes and anti-Stokes components of a second-order Raman mode can be well understood by double resonance Raman scattering.     

Broadband coherent anti-Stokes Raman scattering spectroscopy of nitrogen using a picosecond modeless dye laser

Broadband picosecond coherent anti-Stokes Raman scattering (CARS) spectroscopy of nitrogen is demonstrated using 145-ps pump and probe beams and a 115-ps Stokes beam with a spectral bandwidth of 5 nm. This is, to our knowledge, the first demonstration of broadband CARS using subnanosecond lasers. The short temporal envelope of the laser pulses and the broadband spectral nature of the Stokes beam will enable nonresonant-background-free, single-shot, or time-dependent spectroscopy in high-pressure or hydrocarbon-rich environments. Successful correlation of room-temperature broadband picosecond N2 CARS with a theoretical spectrum is presented.