Scattering media are of great current interest, due to their potential applications in photovoltaic cells, efficient photocatalyzers, random lasers and novel optical functional devices. Here, we have introduced a core–shell scattering medium for random lasing composed by core-shell nanoparticles (TiO2@Silica) suspended in an ethanol solution of Rhodamine 6G. Higher efficiency, lower laser threshold and long photobleaching lifetime were demonstrated in random laser. A promising method called fraction of absorbed pumping (FAP) has been introduced, which opens a new avenue to characterize and study scattering media. In this article, we also investigate the random laser action at the critical regime of localization by increasing considerably the concentration of TiO2@Silica nanoparticles. Narrow peaks arising in the random laser emission spectrum are observed. The classical superfluorescence band of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. However, frontal collection showed the saturation of emission and absorption. The emission spectrum of the peak mode (localized modes) shows approximately equal intensity, indicating suppression of the interaction between the peaks modes. The linewidth of these peaks is lower than that of the passive modes of the scattering medium, which was attributed to an anomalous nonlinear increase of the refractive index by localization.
E. Jimenez Villar, Valdeci Mestre, N. U. Wetter, and Gilberto F. de Sá, "Core-shell (TiO2@Silica) nanoparticles for random lasers," Proc. SPIE 10549, Complex Light and Optical Forces XII, 105490D (Presented at SPIE OPTO: January 30, 2018; Published: 22 February 2018); https://doi.org/10.1117/12.2289228.
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