Ação de um laser randômico no regime de localização induzida em uma suspensão coloidal

Abstract

Anderson localization of light and random lasing at the localization transition are an open research frontier. The first approach to demonstrate experimentally Anderson localization of light in three dimensional systems was based on the increase of the samples dispersion by increasing the scatterer density with the goal of obtaining the Ioffe-Regel criterion of kl = 1, where k is the wavevector and l is the transport length. Howe- ver, this strategy decreases the separation between scatterers and consequently increases near field coupling which hampers Anderson localization. Another, second and less well- known approach, is to introduce correlation in the scatterers position, that is, inducing a certain order in the disorder or, in other words, to introduce disorder in an ordered photonics structure. This strategy was recently demonstrated theoretically by Kravtsov et al and also Dal Negro et al, showing the universality of this phenomenon. They cal- led this phenomenon of correlated long-range hopping correlation-induced localization. We demonstrated experimentally localization of light in 3D induced by correlation in the scatterers position, which was attributed to the long-range Coulomb interaction between the scatterers. Additionally, we proposed that an increase of the silica shell thickness should lead to an increase of the scatter?s hydrodynamic diameter, which would induce a stronger and longer-range Coulomb interaction between the scatterers. In this manuscript we show random lasing in correlated colloidal systems origi-nated by long-range Coulomb interactions between core-shell TiO2@Silica nanoparticles suspended in ethanol solution of Rhodamine 6G. TiO2 nanoparticles with two different silica shell thicknesses (40 nm and 70 nm) were prepared. We find that the Random laser performance improves when the silica shell is thicker (70 nm). Also, light diffraction patterns in both TiO2@Silica suspensions showed strong correlation in the scatterers po- sition, being stronger when the silica shell is thicker. Together with other experimental evidence, we demonstrate that stronger and longer-range Coulomb interaction between the scatterers, caused by a thicker shell in TiO2@Silica nanoparticles, causes a stronger localization of light (higher density of localized states) induced by stronger correlation in the scatterers position.