Tuneable optical gain and broadband lasing driven in electrospun polymer fibers by high dye concentration

The optical gain of blue light-emitting electrospun polystyrene fibers doped with a linear multi-fragment molecular dye based on the combination of fluorine-carbazole functional units is investigated, with the aim of correlating emission properties and the specific material architecture made of either aligned or disordered fibers. Enhanced performance is found in aligned fibers, whose gain spectrum can be finely tuned by varying the dye concentration. Instead, randomly oriented fibers show a manifold spectral line narrowing, resulting in sharp laser peaks superimposed on top of a broad emission band, ascribable to random lasing. In these systems, the increase of the dye content turns out to be effective for both decreasing the lasing threshold by about a factor of 6 and for varying the laser emission wavelength. These results make these arrays and disordered architectures of fibers valuable active media for variable-gain, broadband lasing, which is remarkably important in optical sensing and tunable microlaser devices.