罗丹明B荧光增强苯受激拉曼散射研究

将液芯光纤技术与荧光增强受激拉曼散射技术相结合,能够大大增强受激拉曼散射光谱强度,降低受激拉曼散射阈值。通过对罗丹明B苯溶液在液芯光纤中的受激拉曼散射进行研究,结果表明:荧光染料Rhodamine B可以降低苯溶液的各阶受激拉曼散射阈值近一个数量级;在一定浓度范围内(10-6mol/L~10-8mol/L)各阶Stokes阈值随浓度降低而降低,并在理论上给出了解释。并且理论推导了在荧光种子作用下的四阶耦合波方程。液芯光纤中的受激拉曼光谱技术在对实现宽带受激辐射激光器、种子激光,以及生物大分子结构研究、生物分子的非生物过程研究等领域等有光明应用前景。     

Growth profile of stimulated Raman anti‐Stokes scattering influenced by fluorescence seeding in liquid‐core optical fiber

We demonstrated the growth profile of stimulated Raman anti‐Stokes scattering (SRS) of carbon disulfide (CS₂) influenced by fluorescence seeding of all‐trans‐β‐carotene and rhodamine‐B (RhB) in liquid‐core optical fiber (LCOF). The pump energy which was needed to build up the first‐order anti‐Stokes radiation of CS₂ solutions with the fluorescence seeding was lower than that of CS₂ solutions without fluorescence seeding because of the fluorescence enhancement effect on the intensity of the first‐order Stokes radiation. The first‐order anti‐Stokes radiation of the RhB solution (10⁻⁸ M ) was built up at a lower pump energy than that of the all‐trans‐β‐carotene solution (10⁻⁶ M ), and the intensity of the first‐order anti‐Stokes radiation of the RhB solution was higher than that of the all‐trans‐β‐carotene solution. Simultaneously, the coupled wave differential equations were obtained by the theoretical derivation, and the growth profile of the first‐order anti‐Stokes radiation was theoretically calculated with and without the fluorescence seeding by these equations. Copyright © 2009 John Wiley & Sons, Ltd.     

外部荧光种子植入法增强液芯光纤中CS2的受激拉曼散射研究

本文报道了运用外部荧光种子(罗丹明6G乙醇溶液)植入法对液芯光纤中CS2受激拉曼散射的增强研究。实验结果表明, CS2的二阶、三阶Stokes波分别获得了1.92和11.71倍的增益。并对外部荧光种子植入法增强液芯光纤中受激拉曼散射的机制进行了分析。     

Stimulated Raman scattering influenced by concentration,fluorescence profile and bandwidth of β‐carotene in liquid‐core optical fiber

We demonstrated stimulated Raman scattering (SRS) of carbon disulfide (CS₂) influenced by β‐carotene in a liquid‐core optical fiber (LCOF). Owing to the double fluorescence characteristics and large third‐order optical nonlinearity of β‐carotene, the high‐order Stokes lines, such as the seventh‐order Stokes line of CS₂, can be observed at a relatively low input‐laser power. The thresholds of Stokes lines lowered with the addition of the carotenoid when the concentration of solution was within 10⁻¹² and 10⁻⁷ mol/L; the threshold increments and intensities of Stokes lines were correlative with the fluorescence profile of β‐carotene: when the fluorescence intensity of the wavenumber region on the spectrum was high, the Stokes line intensity was also high and its threshold increment was small, and vice versa. These results are expected to be worthy of the applications on the tunable laser and the seeding laser. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of amplified spontaneous emission and fluorescence of β-carotene on stimulated Raman scattering of carbon disulfide

β-carotene with double fluorescence characteristics and large third-order optical nonlinearities, which is dissolved in the carbon disulfide (CS₂) as the core medium of a liquid core optical fiber (LCOF), is applied in the study of the CS₂ stimulated Raman scattering (SRS). The results of this study show that when the concentrations of solution are more than 3.72×10⁻⁷ mol/L, the amplified spontaneous emission (ASE) of β-carotene is the main factor influencing the threshold and intensity of Stokes lines; when the concentrations of solution are lower than 3.72×10⁻⁷ mol/L, the ASE disappears and the fluorescence plays the key role: The high-order Stokes lines may be observed at very low input-laser power, and the Stokes thresholds decrease as the solution concentration increases. The result may be widely used in the study of broadband stimulated radiation laser and seeding laser. Supported by the National Natural Science Foundation of China (Grant No. 10774057)     

Enhancement CH-SRS of benzene mixing with toluene in liquid-core optical fiber at a low excitation power

Stimulated Raman scattering (SRS) of benzene mixing with toluene is studied in liquid-core optical fiber (LCOF) at a low excitation power 3 mJ/pulse. We obtained the intensive SRS of CH stretching vibration at 3060 cm^?1 [CH-SRS]. Neat benzene or toluene does not show the CH-SRS line under the same experimental condition. The CH-SRS threshold at 3060 cm^?1 for the binary solution was 2.5 mJ/pulse. The results suggest that interaction in molecular vibrations can generate strong CH-SRS in LCOF, we assume that the main mechanism of these phenomena to be the laser-induced plasma (LIP) enhancement to CH-SRS, which may provide a simple way to investigate the intermolecular interaction.     

Continuous wave stimulated Raman scattering of benzene by fluorescence enhancement in hollow fused silica fiber

We present continuous wave stimulated Raman scattering (SRS) of benzene (C₆H₆) influenced by the fluorescent dye m‐cresol purple in a hollow fused silica fiber (HFSF). Because of the transmission loss of the HFSF filled with C₆H₆, the SRS occurs when the Stokes gain equals the transmission loss, with the loss taken at the Stokes wavelength. The 992 cm⁻¹ stimulated Stokes line has been obtained at the pump wavelength 658 nm, which cannot be obtained at 532 nm because the Stokes wavelength (562 nm) does not locate in the transmission loss. Also, the pump power is 35 mW with m‐cresol purple which is much lower than 800 mW without the dye. The profile of the 992 cm⁻¹ stimulated Stokes is changed, and the weak shoulders of the profile are amplified by fluorescence. These results are expected to be of relevance in applications on the tunable Raman laser at new wavelengths. Copyright © 2011 John Wiley & Sons, Ltd.     

High Efficient C6H12 Raman Laser Enhanced by DCM Fluorescence

We report the first-order Stokes output （wavelength of 627.6 nm） from C6H12 enhanced by DCM dye fluorescence with high energy conversion efficiency of 47.9%, quantum conversion efficiency of 56.5%. To our knowledge, it is the highest conversion efficiency of stimulated Raman scattering obtained from liquid Raman laser. A 532nm frequency doubled Nd：YAG laser with 8 Hz repetition rate is employed as the pump source, and the enhancement medium is DCM dye solution in ethanol. The conversion efficiencies at various pump energies and various pump repetition rates are measured and analysed. The enhancement mechanism of SRS together with its potential application is discussed.     

Stimulated Raman Stokes scattering influenced by all-trans-β -carotene in liquid-core optical fiber

We demonstrate stimulated Raman Stokes (SRS) scattering of carbon disulfide (CS₂) influenced by a natural dye named all-trans-β-carotene in a liquid-core optical fiber (LCOF). These Stokes emissions can acquire the extra effects of seeding or suppression, both of which result from the optical properties of the carotenoids. Then, the efficient control of the selective developments of the Stokes lines by the natural dyes is available in LCOFs. Especially, the low threshold of the high-order Stokes lines, such as the 2nd Stokes line of CS₂, can be more easily obtained through the seeding effect. The saturation intensity of the 1st Stokes line can be suppressed more when the concentration of all-trans-β-carotene in CS₂ becomes high. Simultaneously, the threshold of the 1st Stokes line increases with the addition of the carotenoids. This result is expected to be worthy of new SRS-based fiber light sources for bio-medicine applications such as photodynamic therapy.     

Influence of fluorescent dye on the linear polarization direction of stimulated Raman Stokes scattering in liquid‐core optical fibers

We present a simple analytical model to describe the stimulated Raman Stokes scattering (SRS) linear polarization spectroscopy of fluorescent dye solutions in liquid‐core optical fibers (LCOFs). In this scheme, the linear polarization direction of the pump pulse is set parallel to the y‐axis through a straight polarization‐maintaining LCOF, in which the energy of the total optical field is kept invariant, and different fluorescence dyes are used to generate different first‐order Stokes intensities. We demonstrate the SRS of all‐trans‐β‐carotene and fluorescein in carbon disulfide (CS₂) solutions due to the optical field‐induced reorientation effect, which makes the first‐order Stokes polarization direction rotate by an angle of 88° or 61°, respectively. This demonstrates the good agreement between the theory presented and the experiment. Copyright © 2010 John Wiley & Sons, Ltd.     

Stimulated supercontinuum-radiation generation of carbon disulfide by all-trans-β-carotene fluorescence enhancement effect in liquid core optical fibre

We demonstrate stimulated supercontinuum-radiation of carbon disulfide (CS₂) influenced by biological molecules all-trans-β -carotene in liquid core optical fibre (LCOF). By virtue of the broad fluorescence characteristics and large third-order optical nonlinearities of all-{trans}-β-carotene,the high-order Stokes lines of stimulated Raman scattering (SRS) and the multi-order Stokes lines of stimulated Brillouin scattering (SBS) excitated by SRS are observed at low input-laser energies. The results indicate that the fluorescence not only enhances the SRS, but also the SBS. These Stokes lines generate the SRS--SBS supercontinuum radiation (RBSR). A flat-amplitude bandwidth of 110 nm from 515nm to 625nm is observed when a frequency-doubled Nd:YAG laser at 532nm with an energy of 0.86mJ is used. This result is expected to be useful for the multi-wavelength fibre laser.     

Enhanced stimulated Raman scattering in H<Subscript>2</Subscript> by seeding an SRS line into an H-ɛ Balmer line: Amplification-coupled laser wavelength shifter

The stimulated Raman scattering (SRS) in H₂ gas above the dissociation energy limit was recorded using a 266-nm UV laser. All of the observed Stokes and anti-Stokes SRS lines showed a normal behavior except the third Stokes SRS lines at 397.8 nm, which showed a substantial intensity enhancement of about a 36%-conversion efficiency of the pump energy. This enhancement in the SRS line is attributed to the seeding of the SRS line into the Balmer H-? line at 397 nm in molecular hydrogen. To the best of our knowledge, there is no report of any work on enhanced stimulated Raman scattering in H₂ by the seeding of the H-? Balmer line into the SRS line and attaining a very high intensity at the third Stokes SRS lines at 397.8 nm. The cell pressure and the laser pulse energy dependence of these SRS lines substantiate our explanation.     

SDS增溶DCM水溶液的荧光特性研究

研究了十二烷基硫酸钠(SDS) 增溶DCM水溶液的荧光光谱特性。随着SDS浓度的增加, DCM在水中的溶解度大大增加,荧光强度增强;当SDS浓度从0.025 mol·L-1增加到0.5 mol·L-1时,荧光峰值相对强度增强95倍。用532 nm激光激发SDS增溶DCM水溶液获得648 nm的强染料激光输出, 其波长相对于由DCM乙醇溶液获得的635 nm染料激光红移13 nm。利用该溶液荧光对苯的受激拉曼散射(SRS)Stokes波长选择增强。作为对比,用DCM乙醇溶液的荧光对苯受激拉曼散射进行选择增强,结果显示出二者对苯的二、三、四阶Stokes波均可产生放大,但前者最大放大波长位于第三阶Stokes线(632 nm)处,放大因子8.5,后者最大放大波长位于第二阶Stokes线(595 nm)处,放大因子为2.5。另外分析讨论了SDS增溶DCM水溶液和荧光增强的机制及其应用前景。     

染料荧光增强苯的受激拉曼散射

本文报道若丹明6G荧光增强苯的受激拉曼散射一阶Stokes谱线的实验研究,在若丹明6G苯溶液浓度为～10-3mg/ml时,获得了有效的增强,浓度为13×10-3mg/ml时最大增强因子达到32。对增强机制进行了物理解释。     

Enhanced stimulated Raman scattering by intermolecular Fermi resonance

We demonstrate the stimulated Raman scattering (SRS) of a binary solution of toluene and m-xylene at different volume concentrations in liquid-core optical fiber (LCOF). The results show that SRS of three vibration modes of 1002 cm⁻¹,2920 cm⁻¹ and 3058 cm⁻¹ bands are simultaneously generated at some volume concentrations. The 2920 cm⁻¹ band and the 3058 cm⁻¹ band are generated at one time, the SRS thresholds of the first-order Stokes of the 2920 cm⁻¹ and 3058 cm⁻¹ bands are lower compared with the second-order Stokes threshold of the 1002 cm⁻¹ band and the main peak of the 2920 cm⁻¹ and 3058 cm⁻¹ bands changes from the 2920 cm⁻¹ band to the 3058 cm⁻¹ band as the volume concentrations are changed. We assume that these phenomena are attributed to the intermolecular Fermi resonance. Raman scattering cross section (RSCS) theory is used to explain this assumption.     

用激光增益获取弱增益拉曼模式的受激拉曼散射光谱

当酒精的弱增益拉曼模式处于罗丹明640染料分子的激光增益范围时，在由悬垂液滴构成的圆形谐振腔中，观察到乙醇分子C—H伸缩系列模中多个弱增益拉曼模式的受激拉曼散射（SRS）光谱.随着抽运光的增强，迅速增长的强增益拉曼模式的受激辐射抑制了其他弱增益模式的SRS，并导致染料激光的完全淬灭.通过分析圆形腔腔模的光子速率方程和激光染料分子的三能级粒子数速率方程，解释了观察到的实验现象. 关键词： 受激拉曼散射 悬垂液滴 弱拉曼增益模式 激光增益     

DCM荧光增强C3H6O 受激拉曼散射（SRS）的增益特性研究

报道荧光染料DCM对丙酮SRS的高效放大, 研究了DCM中Stokes波的增益特性. 改变DCM乙醇溶 液浓度，变化进入DCM的Stokes光强度以及抽运激光功率，测量并分析了Stokes波增益与上 述条件的关系. 研究结果发现，当DCM浓度为 2×10^-4mol/L时，Stokes波 获得最大功 率增益达到57；抽运激光功率增加或进入DCM的Stokes信号增强时Stokes波输出增强，但 过强的Stokes 信号将导致增益饱和. 关键词： 受激拉曼散射 荧光增强Stokes波 丙酮 DCM     

Random fiber laser of POSS solution-filled hollow optical fiber by end pumping

Random fiber laser is obtained by end pumping a hollow optical fiber (HOF) filled with a dispersive solution of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles and laser dye pyrromethene 597 (PM597) in carbon disulfide (CS₂), in which the concentration is 1.5×10^?2 M for PM597 and 18.5 wt% for POSS, respectively. It is found that the pump light at the one end of the liquid core optical fiber (LCOF) can pass the whole length of LCOF because the POSS nanoparticles were dispersed in CS₂ at a molecular level (1–3 nm) with high stability and without sedimentation. Above the threshold pump energy (～0.81 mJ) the random fiber laser appears coherent and resonant feedback multimode lasing in the weakly scattering system. For the LCOF containing PM597 with the same concentration and no POSS nanoparticles, there occurs only ASE that can be observed under the same experimental condition.     

用染料激光增益降低二元混合物中少量化合物的受激拉曼散射可探测浓度

在二元混合物构成的圆形谐振腔中,用染料的激光增益增强了少量化合物(乙醇溶液中的甲醇、水溶液中的乙醇)的受激拉曼散射（SRS）光谱,将少量化合物在悬垂液滴中的瞬态SRS探测极限提高了近一个数量级. 用受激拉曼散射理论,解释了增强少量化合物SRS的机理. 关键词： 受激拉曼散射 染料激光增益 二元混合物 最小可探测浓度     

The stimulated Raman scattering competition between solute and solvent in Rhodamine B solution

The competition between the stimulated resonance Raman scattering (SRRS) of Rhodamine B (RhB) and the stimulated Raman scattering (SRS) of ethanol (C₂H₅OH) is observed at the RhB in C₂H₅OH solution. For different concentrations of the solution, the peak wavelengths of the SRRS, the amplified spontaneous emission (ASE), the fluorescence and the absorption of RhB are different. The SRRS of RhB and the SRS of C₂H₅OH are simultaneously generated when the concentration of the solution is 10^-5 mol/L and the energy of the excitation laser is 20.4 mJ. Otherwise, only either the SRRS of RhB or the SRS of C₂H₅OH is generated. The SRRS can be amplified by the ASE gain when the SRRS is near the peak of the ASE, and the peak wavelength of the SRRS coincides with the wavelength of the maximal intensity ASE.