Nat. Commun. 9, 3863 (2018)

Although random lasers are attractive due to their design flexibility, the lack of a well-defined, directional output beam hinders their use in some applications. Now, Sreekanth Perumbilavil and colleagues from Finland, Italy, the UK and the US have demonstrated a soliton-enhanced random laser that combines highly efficient operation (9.62%) with a smooth spatial emission profile and high directionality. The team exploit weakly scattering dye-doped nematic liquid crystals (NLCs) that exhibit random lasing but also support propagation of self-guided optical spatial solitons. Specifically, they used an NLC called E7 doped with 0.3 wt% of the dye pyrromethene 597 in planar cells. To generate a spatial soliton, a continuous-wave laser beam at 1,064 nm was launched in a 100-μm-thick, 2-mm-long planar cell containing the dye-doped NLC. The team showed that the direction of emission can be controlled by voltage or other external stimuli, and that the laser can be switched on and off by all-optical means.