基于anti-Stokes Raman散射温度效应的温度解调理论研究

激光脉冲进入光纤中,与光纤分子相互作用,产生Raman散射和Raylei曲散射。由于Raman散射具有温度效应,其散射光强度受温度调制,可作为温度信息的载体,用于温度解调及测温系统设计。本文提出了可行的温度解调方法及理论推导,并推导出单通道和双通道条件下的测温关系,设计出两种条件下的传感器系统。

椭圆偏振激光抽运应变光纤的受激anti-Stokes拉曼散射

研究不同椭圆偏振激光抽运应变光纤产生的anti-Stokes拉曼光谱特征。0 Pa压力时,椭圆偏振光相差180°~360°,激发anti-Stokes光出现几率大于0°~180°的anti-Stokes光。对光纤施加水平单边压力,在一定的压力值下,两种椭圆偏振相差的anti-Stokes光出现几率几乎相等;进一步增大压力,破坏了光纤传输条件,高阶anti-Stokes光消失。椭圆偏振光相差与压力引起的光纤双折射,共同导致了频移和峰值半高全宽的变化。同时,高阶anti-Stokes光谱也存在缺级现象,拉曼响应时间、简并四波混频的出现及其响应时间是引起这种现象的根源。这为光纤激光中抑制、增强或选择某一阶anti-Stokes光谱提供了一种新方法。

火灾烟颗粒Stokes散射矩阵的实验研究

针对火灾烟颗粒的Stokes散射矩阵,利用电光调制器、1/4波片、偏振片及锁相放大器等设计与搭建了火灾烟颗粒光散射实验平台;并基于该平台测量了棉绳阴燃、正庚烷明火及檀香阴燃生成的3种烟颗粒的Stokes散射矩阵中16个元素的角度分布.实验结果表明,这些烟颗粒在光散射过程中都体现出明显的非球形效应,尤其是阴燃过程生成的灰烟颗粒.这说明基于球形模型的Lorenz-Mie散射理论对于分析烟颗粒光散射特征存在一定的局限性,而为了进一步挖掘火灾烟颗粒光散射过程中的光强与偏振等信息,需要建立合理的非球形模型,从而为光电感烟火灾探测技术的发展提供指导与支撑.

FPM DOFS中stokes或anti-stokes的频移分析

近年来分布式光纤传感器（DOFS）发展很快，利用四波混频脉冲移位的分布式光纤传感器（FPMDOFS）是最近提出的一种新型分布式光纤传感技术，本文对FPMDOFS中stokes／anti－stokes频移进行了理论分析，给出频移计算公式，并指出在激励光脉冲功率衰减较大的情况下，应考虑由自相位调制引起的stokes／anti－stokes中心频率偏移。

受激布里渊散射中Stokes光的反Stokes散射与慢光效应

为研究受激布里渊散射(SBS)慢光效应的物理机制,研究了Stokes光与布里渊声场之间的反Stokes散射,以及它与SBS慢光之间的内在联系。理论上证明了在SBS中除了泵浦光外,Stokes散射光与布里渊声场之间也满足散射条件,可发生反Stokes散射。该散射过程是泵浦光的Stokes散射的逆过程,因此泵浦光和Stokes光在布里渊声场中经历往返式散射。在此物理前提下建立了SBS慢光模型,其中Stokes光经历多次散射而光程变大,从而产生了慢光。模型所给出的Stokes脉冲的慢光延迟量与前人得到的结果吻合,表明SBS中存在Stokes光的反Stokes散射,多次散射导致的光程变大是产生SBS慢光效应的物理根源。

基于瑞利散射的大气偏振模式Stokes矢量建模仿真

瑞利散射模型是一种经典的大气偏振模式表征模型,在实际中得到了广泛的应用,但不能通过Stokes矢量描述大气偏振模式的分布特性。基于瑞利单次散射原理,对经典的瑞利模型进行推广,建立一种理想条件下的大气偏振模式Stokes矢量仿真模型。该模型能够对理想条件下大气偏振模式Stokes矢量的分布变化进行建模仿真,利用Stokes矢量可以完备地表征大气光偏振态分布情况,并描述出不同类型偏振光的具体分布特性。通过仿真发现,大气偏振模式的Stokes矢量具有"十"字形的分布形态,整体分布始终保持相对于太阳子午线对称特性,随着太阳高度角的升高各矢量分量逐渐减弱。

随机分布群粒子侧向散射特性Muller-Stokes算法的描述

该文用矩阵元素表示偏振激光束入射时与入射方向垂直的平面上散射光的偏振特征,介绍了使用Muller-Stokes算法来研究随机分布群粒子场侧向散射光性质的方法。用此算法对实验得到的数据进行计算得到的结果表明,散射光强的分布是呈轴对称的,散射光各种偏振特性的变化及用于表示各种特性的矩阵元素主要决定于散射粒子的大小。另外,散射系数亦随粒子直径的变化而变化。

用液芯光纤研究stokes/anti-stokes拉曼强度比测温

液芯光纤可以使拉曼光谱强度提高103倍。研究了在stokes/anti stokes拉曼光谱强度比测温中如何获得理想测温结果的方法。用长为5.20m、内径为50μm的含C6H6和CCl4混合液体的液芯光纤,获得了高强度CCl4的±218cm-1,±314cm-1和±459cm-1的拉曼光谱。利用各光谱带的stokes与anti stokes的强度比(Is/Ia),确定了液芯光纤所在处的温度。实验结果表明,±459cm-1的强度比的实验值与理论值符合得很好,±218cm-1为较好,±314cm-1稍差一些。从理论和实验两方面总结了拉曼频移、光纤损耗、溶剂效应、仪器响应等对测温结果的影响。

受激布里渊散射中Stokes光高频调制的抑制

受激布里渊散射中Ｓｔｏｋｅｓ光高频调制的抑制哈元清杨经国（四川大学物理系成都６１００６４）ＲｅｄｕｃｅｔｈｅＳｔｒｏｎｇＦｒｅｑｕｅｎｃｙＭｏｄｕｌａｔｉｏｎｏｆＳｔｏｋｅｓｉｎＳＢＳＨａＹｕａｎｑｉｎｇ，ＹａｎｇＪｉｎｇｇｕｏ（Ｄｅｐｔ．ｏｆＰｈｙ...

单模光纤中受激布里渊散射的Stokes光频移的温度传感特性研究

首先从单模光纤中声学声子、泵浦光子和stokes光子的频率之间的波矢关系出发,理论推导了单模光纤中的stokes光频移与工作环境温度之间的传感模型。接着设计了一个基于受激布里渊散射(SBS)效应的多波长掺铒光纤激光器的结构装置,并实验测试了该多波长光纤激光器的Stokes光频移随外界温度的变化曲线。实验结果表明:Stokes光频率漂移量和温度之间存在很好的线性关系,且随着温度的升高,高阶Stokes光频移对温度的频移系数高于低阶Stokes光。

受激布里渊散射Stokes脉冲展宽现象抑制研究

针对高泵浦强度下受激布里渊散射(stimulated brillouin scattering,SBS)脉宽压缩过程中出现的Stokes展宽现象,提出了一种抑制展宽、提高压缩率的新方法——驻波驱动SBS压缩结构。此方法以驻波驱动声波场代替传统的噪声起振,加强声波场的同时,固定Stokes产生位置,从根源上抑制了Stokes光展宽现象。通过对照试验,证实了该方法的有效性,抑制Stokes展宽的同时获得了亚声子寿命输出。

Stokes与Antistokes喇曼散截面的温度依赖关系

论述了stokes与antistokes过程喇曼散射截面的温度依赖关系.将这种关系应用于LiNbO_3晶体样品温度的原位测量,发现这种测量温度的方法有较高的精度,对于一些难于直接测温的样品很有效.通过对BaTiO_3喇曼散射514cm^(-1)峰stokes及antistokes相对散射强度的比较,结果BaTiO_3的铁电相变更接近于有序-无序型机制.

Selective excitation of molecular mode in a mixture by femtosecond resonance-enhanced coherent anti-Stokes Raman scattering spectroscopy

Femtosecond time-resolved coherent anti-Stokes Raman scattering （CARS） spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm （corresponding to a saturation iodine vapour as low as about 35 Pa）. The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies （vacuum, heated and pure iodine） in the femtoseeond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.

Simultaneous measurements of global vibrational spectra and dephasing times of molecular vibrational modes by broadband time-resolved coherent anti-Stokes Raman scattering spectrography

In broadband coherent anti-Stokes Raman scattering （CARS） spectroscopy with supercontinuum （SC）, the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of various spectral components of SC in an enough bandwidth. By numerical simulations, the optimal experimental conditions for improving the SC are obtained. The broadband time-resolved CARS spectrography based on the SC with required temporal and spectral distributions is realised. The global molecular vibrational spectrum with well suppressed nonresonant background noise can be obtained in a single measurement. At the same time, the measurements of dephasing times of various molecular vibrational modes can be conveniently achieved from intensities of a sequence of time-resolved CARS signals. It will be more helpful to provide a complete picture of molecular vibrations, and to exhibit a potential to understand not only both the solvent dynamics and the solute-solvent interactions, but also the mechanisms of chemical reactions in the fields of biology, chemistry and material science.

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 π spectral phase step.

Laser Cooling Using Anti-Stokes Fluorescence in Yb^(3+)-Doped Fluorozirconate Glasses

The fluorozirconate glasses ZBLANP( ZrF\-4-BaF\-2-LaF\-3-AlF\-3-NaF-PbF\-2) doped with different Yb\+ 3+ concentration were prepared. The Raman spectra and absorption spectra are measured to substantiate the existence of phonon-assisted emission. After analyzing the normalized absorption spectra of samples with different Yb\+ 3+-doped concentration, we calculated the maximum cooling effect in the 3 wt% Yb\+ 3+-doped sample pumped at 1 012.5 nm. The corresponding cooling capability is about -4.09 ℃/W and the cooling efficiency reaches 1.76%.

Coherent coupling between vibrational modes of C-H bonds at different positions studied by femtosecond time-resolved coherent anti-Stokes Raman scattering

We performed femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） measurements on liquid toluene and PVK film. For both samples, we selectively excited the CH stretching vibrational modes and observed the expected quantum beat signals. The frequency of the well-defined beats is in good agreement with the energy difference between the two simultaneously excited modes, which demonstrates that a coherent coupling between the vibrational modes of the C H chemical bonds exists at the different positions of the molecules. The dephasing times of the excited modes are obtained simultaneously.

NaYF_4:Eu^(3+),Tm^(3+),Yb^(3+)材料中Stokes和反Stokes发光研究

合成了Eu3+,Tm3+和Yb3+掺杂的NaYF4材料。360 nm光激发呈蓝色发光,峰值位于452 nm,对应Tm3+的1D2→3F4跃迁;395 nm光激发呈橙色发光,峰值位于591 nm,对应Eu3+的5D0→7F1跃迁;409 nm光激发呈红色发光,峰值位于613 nm,对应Eu3+的5D0→7F2跃迁;980 nm光激发呈蓝色和红色发光,发光峰位于474和646 nm。蓝光来源Tm3+的1G4→3H6跃迁,红光来源Tm3+的1G4→3F4跃迁。在双对数曲线中,蓝光474 nm和红光646 nm的斜率分别为2.1和2.4,在980 nm光激发下,蓝光和红光发射都是双光子过程。还研究了材料的吸收光谱,并利用X射线衍射,扫描电镜测试了材料的物相结构和微观形貌。结果表明:NaYF4∶Eu3+,Tm3+,Yb3+材料具有较规则的六方相结构,结晶良好。

Theoretical and experimental investigations of coherent phonon dynamics in sapphire crystal using femto-second time-resolved coherent anti-Stokes Raman scattering

We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） technique. The temporal chirped white-light continuum （WLC） is used for the Stokes pulse, therefore we can perform the selective excitation of the phonon modes without using a complicated laser system. The expected quantum beat phenomenon is clearly observed. The theoretical formulas consist very well with the experimental results. The dephasing times of the excited phonon modes, the wavenumber difference, and the phase shift between the simultaneously excited modes are obtained and discussed. This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons.

Analysis of detection limit to time-resolved coherent anti-Stokes Raman scattering nanoscopy

In the implementation of CARS nanoscopy, signal strength decreases with focal volume size decreasing. A crucial problem that remains to be solved is whether the reduced signal generated in the suppressed focal volume can be detected. Here reported is a theoretical analysis of detection limit （DL） to time-resolved CARS （T-CARS） nanoscopy based on our proposed additional probe-beam-induced phonon depletion （APIPD） method for the low concentration samples. In order to acquire a detailed shot-noise limited signal-to-noise （SNR） and the involved parameters to evaluate DL, the T-CARS process is described with full quantum theory to estimate the extreme power density levels of the pump and Stokes beams determined by saturation behavior of coherent phonons, which are both actually on the order of ~ 109 W/cm2. When the pump and Stokes intensities reach such values and the total intensity of the excitation beams arrives at a maximum tolerable by most biological samples in a certain suppressed focal volume （40-nm suppressed focal scale in APIPD method）, the DL correspondingly varies with exposure time, for example, DL values are 103 and 102 when exposure times are 20 ms and 200 ms respectively.