Tailoring Random Lasing Emission by Pulsed Polymer Ablation

Random lasers (RLs) with spatially distributed feedback (SDF) use highly scattering particles, randomly distributed into the gain medium, as feedback elements for lasing action. An alternative approach consists of RLs with spatially localized feedback (SLF) in which the gain medium is enclosed between two scattering surfaces, providing feedback and output coupling. Emission spectra from RLs, both with SDF and SLF, are unpredictable as lasing frequencies are randomly distributed in spectrum. Here, we present a fabrication approach which allows to tailor the average number of lasing modes in RLs with SLF. The active medium is a dye doped polymer film, in which two parallel grooves, placed at a distance of 3 mm, are obtained by pulsed laser ablation with different pulse durations (100 fs and 30 ps) and energies, Ep. The RL with SLF is obtained by pumping at 532 nm a rectangular region placed between and limited by the grooves. Emission scattered from the polymer/air interfaces at the rough groove walls is collected and sent to a spectrometer, see [4] for more details. In Fig. 1 (a) and (b), we show the polymer/air interface at the groove walls obtained with Ep = 170 μJ, and with pulse duration of 100 fs and 30 ps, respectively. Due to the different peak power and repetition rates of the ablating laser sources, we obtain a continuously rough surface with micron sized defects, for the 100 fs pulses, and a smoother surface with craters corresponding to the ablating laser spot, for the 30 ps pulses.