Adaptive pumping for spectral control of random lasers

A laser is not necessarily a sophisticated device: pumping an amplifying medium randomly filled with scatterers makes a perfectly viable 'random laser'. The absence of mirrors greatly simplifies laser design, but control over the emission wavelength and directionality is lost, seriously hindering prospects(1-4) for this otherwise simple laser. Recently, we proposed an approach to tame random lasers(5), inspired by coherent light control in complex media(6). Here, we implement this method in an optofluidic random laser(7) where modes are spatially extended and overlap, making individual mode selection impossible, a priori. We show experimentally that control over laser emission can be regained even in this extreme case. By actively shaping the optical pump within the random laser, single-mode operation at any selected wavelength is achieved with spectral selectivity down to 0.0 6nm and more than 10 dB side-lobe rejection. This method paves the way towards versatile tunable and controlled random lasers as well as the taming of other laser sources.