Study On Whispering Gallery Mode Lasing Threshold Of Rhodamine B In Mixed Solution

Dye laser is device that organic dyes dissolved in the solvent as gain medium, Advantage of the laser is adjustable in a wide range that can realize continuous laser wavelength, solvent of dye and optical cavity has a great influence for the fluorescence quantum efficiency of dye, and the laser threshold and laser emission wavelength tuning range. And the structure of the optical cavity has a direct impact for laser quality factor (Q) and the laser threshold. Evanescent-wave prompting gain coupled fiber laser (EPGCFL) is fabricated by circular section of a bare optical fiber as whispering gallery mode (WGM), and the characteristics of the EPGCFL, including quality factor (Q) very high, lower lasing threshold, simple fabricate. In the EPGCFL, concentration and refractive index(RI) has a great influence for gain and loss value, when dye solution as gain medium. In the experiment, glycerol aqueous as solvent of RhB, researched dye solution concentration and RI influence for EPGCFL. The main research contents as following:First, we researched dye solution concentration influence for EPGCFL. With the increase of the RhB dye concentration of the glycerol aqueous solution, we find that threshold energy becomes low at first and then increases, there is a best dye concentration the solution that correspond to the minimum threshold energy. Based on the lasing theory of WGM of evanescence wave pumped and gain coupled, the calculated results match experimental data well.Secondly, we researched RI influence for EPGCFL. With the increase of the the refractive index, we find that threshold energy becomes low at first and then increases, there is a best refractive index solution that correspond to the minimum threshold energy. Based on the lasing theory of WGM of evanescence wave pumped and gain coupled, the calculated results match experimental data well.Finally, Comparing to the mixed solution of ethanol and ethylene glycol doped by RhB molecules, for the same dye concentration and same RI of solvent solution, we find that the threshold energy of glycerol aqueous solution is lower than of the solution of ethanol and ethylene glycol. Analysising the RhB fluorescence quantum efficiency in different solvents, we explained the experimental results very well.