Lasering in a Waveguide with Scatterers in Diameter 20nm

We report random lasing achieved in a MEH-PPV/glass waveguide with the TiO₂ scatterers in diameter 20nm that is significantly smaller than submicrometre of TiO₂ scatterers in the films or suspensions previously reported on random lasing. The spectral lines are dramatically narrowed by almost two orders of magnitude compared with those excited by a xenon lamp. The amplified spontaneous emission is identified as the dominant mechanism in our system. Light localization might be achieved in a broad class of random materials based on the features of the mean free path l^*=5.4×10⁵nm, kl^*>>1 and the Thouless number 6.73×10^-5 with k being the wave number.