Random lasers in π-conjugated polymer films

Abstract

Mirrorless laser action has been observed in thin films of a π-conjugated polymer at high excitation intensities, which is based on random cavities in the polymer film. The many mode emission spectrum from a stripe excitation geometry suggests true lasing. Moreover, the emission intensity versus excitation intensity shows the characteristic kink associated with lasing threshold. The coherent backscattering technique is used to determine the light mean free path, or the average scatterer separations inside the film. The random scatterers can provide enough feedback to produce narrow emission lines coming from random cavities. Using the Fourier transform of the laser emission spectrum, we show that the random cavities in the film are of order of 15 mean free paths, or 230 μm.