【作者】 门志伟；

【导师】 里佐威；

【作者基本信息】 吉林大学 ， 光学， 2010， 博士

【摘要】 受激拉曼散射在非线性光学、等离子体、拉曼激光器、拉曼放大器等方面有着重要的应用。尤其是石英光纤中的受激拉曼散射研究更得到了广泛的关注,其研究成果扩大了相干光辐射的物理机制,丰富了受激发射的波长。本论文中,我们将荧光种子增强微液滴中受激拉曼散射技术与液芯光纤技术联用,来达到降低受激拉曼散射阈值并且能很好收集和控制受激散射光的目的。本论文主要分三个部分讨论荧光种子对二硫化碳高阶受激拉曼散射阈值、斯托克斯和反斯托克斯生长线型以及一阶斯托克斯线偏振光偏振状态的影响。(1)我们将用含有全反式β-胡萝卜素的二硫化碳溶液作为液芯光纤芯液体,研究全反式β-胡萝卜素对二硫化碳受激拉曼散射的影响,并且进一步做了理论上的拟合和解释。得出以下结论:在不同浓度下,全反式β-胡萝卜素的放大自发辐射或荧光对二硫化碳受激拉曼散射起着主要的增强方式。由于全反式β-胡萝卜素的荧光和液芯光纤的双重增强作用,很小能量激光获得了多级高阶受激拉曼散射。该研究对更深的理解荧光增强受激拉曼散射机理,更深层次探讨光子-声子相互作用的物理机制有着重要的意义。(2)在受激拉曼过程中当相位匹配被满足时,会同时产生斯托克斯和反斯托克斯波,而且它们的强度相差不大,这与自发拉曼散射的情况非常不同。因此,这部分我们分别研究液芯光纤中存在荧光种子(全反式β-胡萝卜素或者罗丹明B)的二硫化碳溶液或纯二硫化碳溶液的情况下,其一阶斯托克斯和一阶反斯托克斯线型生长变化特性。在不同的荧光物质增强作用下,产生的斯托克斯和反斯托克斯线的生长起始点(泵浦能量)和强度有所不同。所以我们可以通过选取不同的荧光种子来控制斯托克斯或者反斯托克斯线的强度,为可控的受激拉曼散射光源提供新方法。(3)在拉曼放大器以及泵浦探测技术中对泵浦光和探测光的偏振状态有着严格的要求,即当泵浦光与探测光的偏振状态平行时受激拉曼散射增益最大。因此我们研究在荧光种子存在条件下,荧光种子性质对一阶斯托克斯偏振态的影响。我们将全反式β-胡萝卜素和荧光素分别溶于二硫化碳溶液中,将其注入空芯石英光纤内,由于液芯光纤的保偏特性,泵浦光和受激产生的斯托克斯光均可以保持其初始偏振状态不变。在光场诱导分子再转向效应下,使得在不同的荧光种子作用下一阶斯托克斯线偏振光转向不同,全反式β-胡萝卜素使得一阶斯托克斯相对于泵浦光转动了88○,而荧光素使其转动61○,同时我们给出了相应的理论推导及其计算。这为泵浦探测技术中偏振状态的选取提供了新的手段。更多还原

【Abstract】 In this paper, the technology of the fluorescence seeding enhancement stimulated Raman scattering(SRS) in the liquid droplet and the technology of liquid-core optical fiber(LCOF) were used together in this study to lower the threshold of SRS and improve the collection of scattering light, and control of the scattering light. This paper mainly studied of the influence of fluorescence seeding to the SRS high-order Stokes threshold, profile and concentration of carbon bisurfide(CS2)solution, to the growth profile and threshold of Stokes and anti-Stokes, to the polarization state of one-order Stokes , respectively.(1) All-trans-β-carotene with double fluorescence characteristics and large third-order optical nonlinearities, which is dissolved in the CS2 as the core medium of a LCOF, is applied in the study of the CS2 SRS. The results of this study show that when the concentrations of solution are more than 3.72×10-7mol/L, the amplified spontaneous emission(ASE) of all-trans-β-carotene is the mainly effect to the threshold and intensity of Stokes lines; when the concentrations of solution are lower than 3.72×10-7mol/L, the ASE disappears and the fluorescence is the mainly effect: due to the double effects of the broadband fluorescence and LCOF, the high-order Stokes lines can be observed at a very low input-laser power, the seventh-order Stokes line was observed using the all-trans-β-carotene solution of 10?7 mol/L, the pump laser with repletion rate 1 Hz, and 0.86mJ pulse energy, Fig.1; the concentrations were within 10?12 and 10?7 mol/L, and the threshold of the Stokes lines decreased with the increase of the concentration of all-trans-β-carotene,Fig.2; the threshold and intensity of the Stokes lines of CS2 had a close Relationship with the fluorescence profile of all-trans-β-carotene,Fig.3. The results have the significance to deeply understand the theory of fluorescence enhancement SRS, to use the all-trans-β-carotene in the abiological field, and it can be widely used in the study of broadband stimulated radiation laser and the seeding laser.(2) Both Stokes and anti-Stokes waves are simultaneously generated with comparable intensity in the SRS process. This is very different from the case in spontaneous Raman scattering and can not be understand as a stimulated two-photon process since the anti-Stokes wave then would be absorbed instead of generated. Yet it can be explained readily by the coupled wave description. We demonstrate theoretical derivation coupled wave equations(1) of fluorescence enhancement SRS effect:And study on the effect of fluorescence enhancement to the first-order Stokes and the first-oder anti-Stokes intensity, when the all-trans-β-carotene or Rhodamine B(RhB) CS2 solutions are injected in the LCOFs, the all-trans-β-carotene fluorescence enhances the intensity of the first-order Stokes line, but the RhB enhances the intensity of the first-order anti-Stokes line, Fig.4; And the growth profiles properties of Stokes and anti-Stokes are changed owing to the fluorescence enhancement effect: the first-order anti-Stokes radiation can be built up at 1.1 and 0.7mJ of pump energy in the all-trans-β-carotene solution and RhB solution, respectively, when both the solutions’first-order Stokes thresholds are at 0.4 mJ, and the first-order Stokes intensities are similar at about 0.018 mJ (Fig.5). The intensity of the first-order Stokes is far away from the saturation intensity when the first-order anti-Stokes intensity builds up. So, we can control the intensity of Stokes or anti-Stokes by using different fluorescence seeding, also provide a controllable SRS light source for photodynamic therapy.(3) There is an importance of matching the polarization directions of the pump and probe waves, SRS nearly ceases to occur in the case of orthogonal polarizations. On the other hand, when the polarization directions of the pump and probe waves are maintained in the Raman amplification and the pump-probe, a large SRS gain will be obtained, as expected theoretically. So we demonstrate the influence of fluorescence property to polarization state of the first-order Stokes. In the dynamical description of SRS in a single mode silica fiber, the pump pulse and the Stokes light have the same linear polarization direction (see Fig. 6(a) without thefluorescent dye in LCOF). However, when the fluorescent dye is dissolved in the Raman medium, the linear polarization direction of the Stokes light cannot be confirmed, and an angleθbetween the pump pulse and Stokes light is assumed; a schematic diagram is shown in Fig. 6(b) with the fluorescent dye in an LCOF.The all-trans-β-carotene or fluorescein are dissolved in CS2 solutions, and them are injected in the LCOF, the pump purse and first-order Stokes linear polarization do not change owing to the straight polarization-maintaining LCOF. Due to the optical field-induced reorientation effect, which makes the differnet polarization direction of the first-order Stokes using the different fluorescence seeding. The first-order Stokes polarization direction rotate an angle 88○or 61○, when the fluorescence seedings are all-trans-β-carotene or fluorescein, respectively, Fig. 7, which is good agreement between the theory presented and experiment. The results provide a new method to the development of the pump-probe and Raman laser.更多还原