Mechanism of Low Threshold Lasing of Dye Solution Embedding in Nanoparticle Fractal Aggregates

We study the single-photon and two-photon induced emission properties of dye solution embedded with nanoparticle fractal aggregates. The spectral and temporal experimental results show that the lasing threshold of single-photon absorption of dye solution embedded with TiO₂ nanoparticle fractal aggregates is significantly reduced compared to that of a neat dye solution; while that of two-photon absorption does not. These experimental results imply that this low threshold single-photon absorption lasing mainly results from the mechanism of random walking, instead of Anderson localization, unless something about two-photon induced emission is unknown.