Anisotropic behavior of random lasing in a highly concentrated dye solution

Angular dependence of the diffusive random laser (DRL) emission is assessed due to excitation of a highly concentrated solution of Rhodamine 6G (Rd6G) comprising monomers and dimers. Dimerization at extremely high concentrations leads to the random fluctuation of the dielectric constant in gain medium. As a result, aggregated dye molecules provide multiple scattering events for propagating photons which is confirmed by enhanced backscattering (EBS) test. This scattering feedback besides Försteŕs resonance energy transfer (FRET) from monomers to dimers provide RL spikes over low quantum yield dimeric fluorescence spectra. The unique spectral feature of RL emission is strong dependence on the angle of detection that results from anisotropic inner filter effect (IFE) within the gain volume due to local excitation of the medium by a pencil-like beam of laser. The results have a merit of importance in optical characterization of the media in which the fluorophores can aggregate significantly.