Tuning the efficiency of Random Laser Generation in a Suspension of ZnO Nanoparticles by Means of its Directional Freezing

In this paper, we introduce a novel approach to control the random lasing based on multiphoton luminiscence in Zinc oxide (ZnO) nanoparticle water suspension during its guided freezing process. The freezing process leads to the formation of a particle layer on the ice surface, consequently reducing the photon’s scattering mean free path in the medium, as well as increase in the efficiency of the second harmonic generation. This results in a lowered random lasing threshold in the system. The post freezing threshold, under the 355 nm wavelength excitation, decreases by an order of magnitude. These effects may have several applications, including the phase transition sensing, monitoring the evolution of porous structures via the ice-templating technique, controlling the random lasing mode, and enhancing various nonlinear optical processes’ effectiveness for nanoparticles and sub-micron particles in suspensions.