Model for bichromatic laser emission from a laser dye with nanoparticle scatterers

In this work, we present model for bichromatic laser emission from laser dye solutions containing randomly distributed scattering particles. We suggest that bichromatic emission is produced by two fluorescent aggregates: monomers and dimers. The shorter-wavelength laser peak was attributed to the monomer emission and the secondary longer-wavelength peak was attributed to the dimer emission. From neat dye solutions, using absorption and emission spectroscopies, the monomer and dimer absorption and emission cross sections were obtained. The partial overlap between the dimer absorption cross section and the monomer emission cross section indicates a unidirectional radiative and nonradiative energy transfers from excited monomers to fundamental dimers. The dynamics of the laser emission was modeled by a set of rate equations, whose solutions agree with our experimental data. It is also shown that nonradiative energy transfer plays a very important role in the dimer laser process, and helps to explain the relatively strong dimer laser peak intensities.