Molecular Energy Coupling And Transfer Enhancement To Stimulated Raman Scattering

The classical and spontaneous Raman scattering have been new developed and promotedwhen laser was produced. Some Raman mediums have the stimulated process while laserenergy is raised in some conditions, which is the stimulated Raman scattering (SRS). SRSwidens the physical mechanism of the coherent light radiation, enriches the range of thewavelength of the stimulated radiation, opens up a new domain of laser interaction withmatter, and provides an effective way to explore the structure of matter. SRS is extensivestudied from it was found.Recently, researchers work at promoting intensity of SRS and lowing threshold of SRS,the fluorescence seeding enhancement SRS in the liquid droplet lows threshold of SRS.Liquid core optical fiber (LCOF) technology was successfully used by our team to lowerthe threshold of SRS and promote the intensity of SRS. the technology of the fluorescenceseeding and the technology of LCOF were used together to obtain good results.Researchers find that Fermi resonance and laser-induced plasma (LIP) will be affectedSRS.In this study, we pay attention to the enhancement ways of SRS, study of three kindsenhancements ways of SRS, which are intermolecular Fermi resonance enhancement SRS,LIP enhancement SRS, and fluorescence seeding enhancement SRS. We according to thetheory basis of intermolecular energy coupling and transfer, enrich enhancement theory ofSRS, obtain some innovative achievements:1. Intermolecular Fermi resonance of toluene and m-xylene enhances SRSIntermolecular Fermi resonance requires a close match of the vibrational energy levelsand an appropriate dependence of the intermolecular potential on the normal coordinatesfor the two vibrational modes, and intermolecular Fermi resonance can involve couplingbetween fundamental vibrations on two different molecules.The physical mechanism of intramolecular and intermolecular Feimi resonance isstudied. Vibrational mode energy of one Raman molecule is transferred to another Raman molecule, which results in the Raman scattering cross section (RSCS) of latter increase,SRS of weak vibrational mode is generated. The Fermi resonance are generated between2920cm^-1and3058cm^-1vibrational modes of toluene and these modes of m-xylene, whichmake that3058cm^-1vibrational mode energy of toluene transfers to the same mode ofm-xylene, and2920cm^-1vibrational mode energy of m-xylene transfers to the same modeof toluene. In this study, we obtain SRS of2920cm^-1mode of toluene and3058cm^-1modeof m-xylene.2. LIP enhances SRS of the mixing solution of benzene and tolueneWe study of the enhancement effect of LIP to RSCS of C-H, and the concentrationrelationship of mixing solutions. When volume concentrations are50%and40%, C-Hstretching vibration3060cm^-1line of weak Raman gain mode is stimulated. When LIP isgenerated in the mixing solution, the homodimer cation (toluene–toluene)+and theheterodimer cation (benzene-toluene)+in plasma cloud enhance RSCS of benzene3060cm^-1C-H mode. The C-H mode energies of two cations transfer to C-H mode of benzene,which lead to increase of benzene Raman gain factor, and generate C-H SRS of the weakRaman gain mode. An additional electric field is formed by the cations and the electrons,which enhances the induced dipole moment of benzene and C-H vibrational mode ofbenzene easily is generated.3. fluorescence molecule enhances SRS of carbon bisulfideAt different concentrations of solution, it had the different enhancement effects ofall-trans-β-carotene on SRS of CS₂. when concentration are from10^-5to10^-6mol/L,amplified spontaneous emission (ASE) can exponentially enhance the intensity of Stokeslines and lower the threshold of SRS; when concentration are from10^-7to10^-12mol/L, thefluorescence can linearly enhance the intensity of Stokes lines and lower the threshold ofSRS at low concentrations. The physical mechasim is that energy of fluorescence moleculetransfers to Raman molecule and increases SRS intensity, and lows SRS threshold. Theall-trans-β-carotenen has a broadband fluoresncen and large third-order nolinear opticalcoefficient, it is used into the LCOF, which lowes SRS threshold of CS₂, the seventh-order SRS of CS₂is generated using the0.86mJ energy.In a word, these three kindes enhancement ways are energy coupling and transferbetween Raman medium and fluorescence, or in Raman mediums. The result is thatpromotes initial Raman quantum noise, or enhances third-order nonlinear opticalpolarizability of Raman medium, which result in lowing the SRS threshold and promotingthe SRS intensity. The results have potential application in intermolecular science.