Exciting Wavelength and Concentration Related Two-Photon Fluorescence of Single and Mixed Laser Dyes

Two-photon nonlinear process induced fluorescence of Rhodamine 6G (R6G), Rhodamine B (RB), and their mixed aqueous solutions in mass proportion of 1:1, is experimentally observed by different exciting wavelengths. It shows that, for each sample, the exciting wavelength can influence the fluorescence intensity considerably but only slightly influence the peak wavelength of the spectrum. The optimal exciting wavelengths of R6G and the mixed dyes are around 700 nm. While for RB, the optimal exciting wavelengths can be 700 nm and 620 nm. For each dye sample, the spectral red-shift will occur as increase of the solution concentration. The mixing of the two dyes will cause the spectral red-shift with regard to the single dye under our experimental conditions. Moreover, in comparison, at lower concentrations, the mixed dye has relatively intense fluorescence. This work is of significance for determining the optimal exciting wavelength and developing the tunable two-photon dye lasers.