Random lasers are cheap and easy to fabricate, having several different applications such as early cancer detection, encryption and Speckle-free imaging. However, few fabricated random lasers present high efficiency, which limits their possible applications. In a recent work, our group achieved a record efficiency by developing random lasers that use compacted, polydispersed yttrium vanadate doped with neodymium (Nd3+:YVO4) powders to create separate regions for gain and light diffusion. Large particles are responsible for the light diffusion, while the small particles that occupy the spaces between them create gain pockets, absorbing the pumped light. In this work, this strategy is refined by using passive particles (SiO2) for light diffusion, restricting the laser active particles to the gain pockets. The first attempt with this strategy used 30% of Nd3+:YVO4 small powders and 70% of large SiO2 particles. Without any further optimization, the result achieved is already 40% of the highest obtained efficiency in the previously studied Nd3+:YVO4 polydisperse sample, showing a promising result to further improve this new strategy and reach even larger efficiencies with less laser active material.
Understanding light absorption in random lasers and its distribution within the scattering gain media is a key issue to increase the lasers’ efficiency. Here we compare monodispersed and polydispersed powders of Nd3+:YVO4 and investigate the influence of the powder size distribution on scattering mean free path, absorption volume and, eventually, the lasers efficiency. The highest efficiency is achieved for polydispersed powders and we conjecture that these polydispersed powders, composed of pockets containing small grains trapped between large particles, present locally higher pump power densities than the monodispersed powders. We establish a figure of merit, based on measurable powder parameters, that agrees well with the obtained output power results of the monodispersed and polydispersed samples.
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