We report on the observations of coherent random lasers in weakly scattering polymer films embedded with silver nanoparticles. The dominant oscillation cavity calculated from the ensemble-averaged power Fourier transform spectrum of single-shot emission spectra is shorter by more than two orders of magnitude than the scattering mean-free path, indicating that the oscillation cavity is loosely associated with multiple scattering. We suggest that the coherent feedback arises from the cooperative effect of light scattering and field enhancement in the vicinity of silver nanoparticles.
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