Inflection point of the spectral shifts of the random lasing in dye solution with TiO2 nanoscatterers

摘要

We report the inflection point of the spectral shift of random lasing, from blue shift to red shift, in Rhodamine 6G dye solution with TiO2 nanoscatterers under picosecond pulses pumping, on increasing the scatterer density for certain dye concentrations. The red shift, resulting from the re-absorption and re-emission of the dye, indicates a longer optical path length of the emitted laser travelling inside the media. The diffusion theory is provided to show the discrepancy in the theory and the experimental results, which show that the light stays in the medium longer than the theory predicts. So this inflection point shows that the system changes from a diffusion system to a weakly localized one. The spectral width shows similar behaviour, for a longer optical path length results in a broader spectral width.