Inflection point of the spectral shifts of the random lasing in dye solution showing transformation to weak localization

Abstract

ABSTRACT We studied the spectral shift of random lasing in the Rhodamine 6G dye solution with TiO 2 nanoscatterers under picosecond pulses pumping. The red shift, resulting from the re-a bsorption and re-emission of the dye, indicates a longer optical path length of the emitted laser traveling inside the medium. Thus the optical paths of the random laser in the solution can be estimated using the values of red shifts for different dye concentrations and scatterer densities. The diffusion theory is provided and the theoretical results agree very well with that calculated from the red shifts before the inflection points appear for increasing scatterer density. The followed increasing scatterer density results in the lights staying longer in the medium, in contrast to that predicted by the diffusion theory. So it is clear that the inflection point shows that the system is changing from a diffusion system to a weakly localized one in which the light stay longer because of the localization. Keywords: Random laser, Inflection point, Spectral shift, Op tical path, Dye solution, Picosecond pulse pumping