Random lasing emission tailored by femtosecond and picosecond pulsed polymer ablation.

We report the realization of random lasers with spatially localized feedback in which the average number of lasing modes is tuned via the fabrication process. The scattering elements required for optical feedback are obtained by short-pulsed laser ablation. By varying the pulse parameters, we control the scattering properties of the induced defects and, thus, the emission spectra. We demonstrate a large variety of spectral signatures typical of resonant random lasing with sub-nanometer linewidths, low thresholds (about 40 pJ/µm2), and single-to-multimode emission. Our simple approach allows us to obtain optical resonators with sharp linewidths at frequencies covering the entire gain window for multiple applications.