Influnce Of Fluorescence On Stimulated Raman Scattering Of Carbon Bisulfide Molecule

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.