【作者】 王梓；

【导师】 夏元钦；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2011， 硕士

【摘要】 相干反斯托克斯拉曼散射(Coherent Anti-Stokes Raman Scattering, CARS)是一种与分子内部振动能级相关的三阶非线性效应。CARS过程是一种相干过程,其具有信号强,方向性好等优点。因此CARS光谱技术经常被用来进行痕量分子探测,燃烧测温。将飞秒时间分辨技术引入到与CARS光谱技术中可以深入研究分子的超快振动过程。而将显微技术与CARS光谱技术相结合,可以实现对样本的无损伤高分辨率成像。这样可以使我们在时间上的动力学方面与空间上的结构两个方面更全面地了解样本信息。本文主要对时间分辨CARS与CARS显微技术应用进行研究。本文首先对飞秒时间分辨CARS光谱进行了理论研究,结合耦合波理论与微扰法得到时间分辨CARS信号强度的基本公式,并着重讨论了影响信号光强的决定性因素—三阶非线性极化率,讨论不同共振条件下的三阶非线性极化率的表达形式。在研究完CARS的基本理论之后,本文搭建了一套完整的时间分辨CARS实验系统,本系统结合了空间滤波,频域滤波与锁相放大技术,使本系统具有信噪比高,稳定性好的优点,可以有效的减弱光源漂移对实验系统的影响。并使用本系统测量了CARS信号输出特性,测量了乙醇和共掺固体染料的CARS光谱,并初步分析了固体染料内部的拉曼能级信息。同时证明了通过改变入射光的偏振方向,可以实现选择性的激发拉曼振动模,这种方法在显微成像中也有一定应用。随后使用双光束和三光束时间分辨CARS光谱分别研究了BBO晶体、二硫化碳溶液和若丹明590溶液的超快振动动力学过程。BBO晶体在3000cm-1附近有两个振动能级,两个振动模间能量无法传递,并且晶体对应均匀加宽的失相时间T2远长于非均匀加宽的失相时间T2*;而二硫化碳在3000cm-1附近有三个振动模,其中两个振动模具有非常快的传递途径,通过加入四氯化碳证明分子间相互作用减弱导致振动模结构变化发生红移;对于若丹明590溶液,发现其T2与T2*基本相近。最后我们又理论研究了CARS显微技术,通过角光谱方法得到了高数值孔径物镜后的光场分布,并得到了光场分布随着物镜数值孔径,入射光束腰斑半径的变化情况。进一步分析了每一点CARS光强分布和CARS光场在空间分布随着散射体大小的变化。更多还原

【Abstract】 Coherent Anti-Stokes Raman Scattering (CARS) is a kind of third order nonlinear effect related to the vibrational energy level of molecule. CARS is a kind of coherent process a nd t hus ha s the a dvantage of hi gh s ignal i ntensity and good di rectivity. Therefore, CARS technology is often used to detect the trace molecule and measure the combustion temperature. By introducing femtosecond time-resolved technology to the CARS spectrum, we could obtain the ultrafast vibrational process of molecule. And By combining t he m icroscopy w ith C ARS s pectrum, w e c ould get the hi gh r esolution micrograph noninvasively. This means that we can get more information of the sample from both time resolved dynamics aspect and spatial structure aspect. This thesis will mainly focus on the two applications of CARS spectrum that have been just mentioned.This dissertation first does some theoretical research on femtosecond time-resolved CARS. By combing coupled wave theory and perturbation method, we obtain the basic expression of t ime r esolved C ARS signal. T hen w e mainly f ocus on t he t hird order susceptibility which is the main factor that determines the CARS signal. We discuss the concrete expression of the third order susceptibility of different resonant condition.After discussing the basic theory of CARS, we construct the time resolved four wave m ixing e xperimental system. T he sys tem expl oits space f iltering, f requency filtering and Lock-in Amplifier technology, which make the system have the advantages of high S/N and stability. The system could also effectively reduce the influence of the drifting of the laser source. We detect the CARS spectrum of alcohol and co-doped solid dye. We preliminarily research the raman energy level of the solid dye. We also prove that by altering the polarization of the incident pulses, we could selectively excite the raman mode of the molecule, which extends the application region of the system, this method may also be very useful in the application of CARS microscopy.Then we used two pulses and three pulses time resolved CARS spectrum to study the ul trafast dyna mic of B BO c rystal, carbon disulfide solution a nd R hodamine 590 solution. BBO crystal has two vibrational energy levels near 3000cm-1 and the energy cannot be transmitted between two levels. We also find that the dephasing time constant T2 due to homogeneous broadening is much longer than the dephasing time constant T2* due to inhomogeneous broadening. Disulfide solution has three vibrational levels near 3000cm-1, and two of them have a very fast energy transfer path. By adding CCl4 to the disulfide solution we find that the weakening of the interaction between CS2 molecules will change the energy structure of the solution and the energy level will shift to the red side. For Rhodamine 590 solution, the dephasing constants T2 and T2* are almost equal. Finally w e do s ome t heoretical research on C ARS microscopy, by us ing a ngle spectrum method w e obt ain t he l ight i ntensity di stribution ne ar t he f ocus of high numerical aperture objectives. We also obtain relationship between the transverse and longitudinal distribution of light intensity near the focus and numerical aperture and the waist radius of the incident pulse. We further research the CARS intensity of every point near the focus, we also obtain the change of the CARS intensity distribution in space with the scatter size.更多还原