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液芯光纤受激拉曼散射研究

Research about Stimulated Raman Scattering in Liquid Fiber

【作者】 陈建

【导师】 里佐威;

【作者基本信息】 吉林大学 , 光学, 2004, 硕士

【摘要】 激光拉曼光谱是研究分子结构的重要工具,在分子光谱中占有重要地位。拉曼光谱的强度、频移、线宽、特征峰数目,与分子的振动能态、转动能态、对称性等内部结构有紧密的联系,因此拉曼散射信号中包含了大量的分子内部信息。但是自发拉曼散射是一种十分微弱的效应,散射截面的典型数值要小于 10?30cm2 。虽然说,激光的问世使拉曼光谱在实践上发生了革命性的变化,但是拉曼效应是如此微弱,必须用特殊的检测手段才能观测到光谱,而且微弱的噪声光就能屏避掉所要观测的谱,这限制了拉曼光谱在很多领域的应用。 而有着由于增益高,有很强的信号,高泵浦光转换效率的受激拉曼散射的发现,使得拉曼效应可以应用到更多的领域。受激拉曼散射现象是属于非线性光学效应,最早是在 1962 年,由 E.J.Woodbury 和W.K.Ng 发现,自发现受激拉曼散射现象以来,利用受激拉曼比泵浦光的光谱范围宽、转换效率高及单色性好等特点,人们将受激拉曼技术广泛应用于包括信息技术、光通讯、光谱探测、激光技术、传感技术等多领域。 液芯光纤(Liquid-core optical fiber,LCOF)是一种新型结构的光传输元件,它采用液体材料作为内芯,石英、玻璃、聚合物材料等作为光学包层,硅橡胶等作为保护层,具有较大芯径、较大数值孔径,并且具有光谱传输范围广、光谱传输效率高、使用寿命长等特点。对于吸收光,根据郎伯-比尔定律增大光谱仪器中样品吸收池的长度,光谱仪器的灵敏度将随之等倍提高。液芯光纤技术自上世纪发明起,就广泛的应用于拉曼光谱的研究。而且对于散射光,当激光入射到液芯光纤内,被激发的拉曼光随入射光的传播不断地被累积加强,由于 第 55 页<WP=61>吉林大学硕士学位毕业论文液芯光纤可以很长,拉曼光在光纤内得到“放大”。本论文中结合了受激拉曼效应及液芯光纤技术,实验证明利用液芯光纤技术可以降低受激拉曼散射阈值两到三个数量级,这是一种新的光谱技术手段。结合液芯光纤技术,可以大幅度降低受激拉曼振荡发生的阈值,在一定程度上可避免普通的受激拉曼振荡对活性拉曼产生的选择性,从而使受激拉曼光谱也可作为一种有用的光谱工具应用于物质分析及生物分子探测等方面,发挥受激拉曼光谱增益高,信号强,泵浦光强的转换效率高,灵敏性强等长处。在实验中采用的液芯光纤是使用德国进口石英拉制的光纤,在两面加上优质石英玻璃耦合头,充入实验样品制作而成,使用的光谱仪器为(Dilor-Omars 89 光谱仪)。本论文对纯溶剂(二硫化碳)及在溶剂中掺入不同浓度的荧光染料(β-胡萝卜素)的受激拉曼谱进行了研究,共有 10-6~10-8mol l 及纯溶液四个样品,在实验中获得了在改变激发光功率时的受激峰变化曲线。从实验过程中,充分验证了液芯光纤可以降低受激拉曼散射阈值的设想,在对实验数据的研究过程中还发现,当在溶剂(二硫化碳)中掺入不同量的溶质(β-胡萝卜素),二硫化碳的受激拉曼阈值及受激拉曼峰的饱和强度,随着溶质浓度的变化而变化,总的变化规律为,二硫化碳的一阶受激拉曼 Stokes 线的受激阈值随溶液浓度的变小而变小,但是变化不是成线形关系,当浓度小到一定程度,受激阈值的变化就不是很明显,另外受激谱线的饱和值随溶液浓度的增大而变小。这种现象产生的原因是当某种拉曼散射液体的某阶 Stokes 谱线落入某种染料的荧光谱带内,而激发光谱线落入该荧光物质的吸收带内,则染料荧光可选择性增强该拉曼散射液体的该阶 Stokes 谱线,其它未落入荧光谱带内的谱线可被削弱。 第 56 页<WP=62>吉林大学硕士学位毕业论文在论文中还发现,随着光纤长度的增强,可以受激拉曼散射的阈值是可以降低的,但是光纤损耗等耗散效应也随着光纤长度的增强而增强,这说明有一个平衡点,使得光纤的累积作用同耗散作用达到平衡,这就是光纤的最佳长度,通过分析得到光纤最佳长度为2 αp ,αp为光纤及样品对斯托克斯光的损耗因子,可见随着光纤研制技术的发展,光纤最佳长度可以越来越长,而受激拉曼散射阈值会降的更低。液芯光纤受激拉曼散射研究提供了一种可以大幅度降低受激拉曼散射阈值的方法,从而可以在没有高功率的激发光时,能够得到受激拉曼谱,这在分子结构研究,光谱探测,传感技术等领域,有着很强的应用性。而且论文实验过程中,发现的受激拉曼阈值及受激光谱线的饱和值随着荧光染料浓度的不同而发生变化的现象,为实现可控的受激拉曼效应提供了一种可行的实验方法。根据光纤受激拉曼散射的效应制成的宽带可调谐的光纤拉曼激光器(RFL)用于光纤拉曼放大器(FRA),目前光纤拉曼激光器的研究正成为大功率单模激光器的一个研究热点。随着液芯光纤技术研究的深入,液芯光纤在这一领域将会得到更广阔的应用。本论文中所进行的受激拉曼阈值的研究,在国内外未见相关报道,是全新的研究,这种研究为分子探测,分子结构研究提供了一种全新的实验技术,随着技术手段的成熟必然会对各种领域中拉

【Abstract】 For many years laser Raman spectroscopy has been an importanttool for the investigation of microscopic molecular structure. Its intensity,frequency shift, line width, characteristic peaks and so on have closerelation with molecule’s vibration, rotation, symmetry property and otherelse information of fine-structure. But Spontaneous Raman Spectroscopy isa kind of weak spectroscopy, and a representative data of scattering sectionis below 10 ?30cm .Of course ,along with invention of laser ,Raman 2Spectroscopy be used in many fields .Raman Spectroscopy is still so weakthat we need special instrument to get Raman Spectroscopy and only littlenoise of light could shield correct Raman Spectroscopy .All of these haverestricted applications in many fields. Discover of Stimulated Raman Scattering (SRS)that hascharacteristic of high reciprocal coefficient ,strong signal , high transitionefficiency etc. ,let Raman Spectroscopy be used in a wider field .SRS isnon-linear optic phenomena ,and it be discovered by E.J.Woodbury andW.K.Ng at 1962.Since discover of SRS ,we utilize its wide range ofspectroscopy , high transition efficiency and homochromy to apply it in thefield of information technology ,optics communication , spectrumtechnology ,laser technology , sensor and otherwise. Liquid-core optical fiber(LCOF) is a new type component ofoptic ,and it be consisted of liquid core , envelope (quartzose ,glass orpolymer) ,and a safe-layer .LCOF has a bigger diameter and IA than solidfiber , and LCOF have some characteristics include wide range of spectrumtransmission ,high transmission efficiency and long used life .Toabsorption light ,longer length of absorption pool ,more delicacy fromLombard-Bill law .LCOF have been used for Raman Spectroscopy since itinvented .To scattering spectroscopy , intensity of spectrum will enhancewith that laser transmit in fiber .Because a fiber could be very long ,soRaman spectrum be “magnified” in fiber . Threshold value of SRS can be 102~103 lower if applying thetechnique of liquid core optics fiber (LCOF) together with stimulatedRaman effect . This is a new experiment technique .Through application ofLCOF ,we can get SRS spectrum at low laser power, and avoid the choiceof Raman matter that could bring SRS .So we can use SRS as a tool in thefield of matter analysis and biology molecule detect ,the strongpoint ofSRS could be exerted . 第 58 页<WP=64>吉林大学硕士学位毕业论文 The fiber used in my experiment is made of high quality quartz ,andits two side is enveloped with quartz coupling- component. Thespectrophotometer is a Dilor-Omars 89 made in France .In this paper ,sample that we used include a pure solvent(CS2) and 10-6~10-8 mol lβ-carotene in CS2, we get the SRS spectrum under different laser power . Through experiment data, we prove that threshold value of SRScould be reduced in LCOF. Analyses the data ,we detect that the thresholdvalue and the max peak value of SRS will change when the concentrationof β-carotene is different . Rule is :to 1st stokes SRS spectrum, thresholdvalue will reduce if the concentration of β-carotene in CS2 decrease, butthe relation is not linearity; the max peak value will increase whenconcentration decrease. Reason of this phenomenon is when Stokes line isin the fluorescence range of another matter, and the wavelength of laser isin the absorption range of this fluorescence matter. Then the Stokes line beenhanced and other Stokes lines out of the fluorescence range areweakened. In the experiment, we find that wasting in optical fiber is largeralong with longer fiber. So, there is a point that the enhance and ullagecould be balance, The value of this point, called the optimum length or theshortest length, can be computed by a formulae, which can give off aconclusion L = 2αF, namely the value of the sho

  • 【网络出版投稿人】 吉林大学
  • 【网络出版年期】2004年 04期
  • 【分类号】O436
  • 【被引频次】2
  • 【下载频次】428
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