Blue and infrared laser action in strongly scattering Nd:alumina nanopowders

Summary form only given. In powders doped with rare earth and transition metal ions, laser action in the multiple-scattering regime has been reported by several researchers. Lossless powders in which gain is encountered are sometimes referred to as "laser paints." These media have interesting properties which may be useful for speckle-free lithography at sub-micron dimensions or bright, omni-directional displays or light sources in conducting films of arbitrary shape. But highly-scattering powders are difficult to pump and study optically because the very scattering which provides the feedback for laser action causes pump light to be scattered backwards very efficiently as it enters the medium. Consequently lasing processes have to our knowledge not been investigated under scattering conditions strong enough to cause an Anderson transition to a regime with highly localized electromagnetic "transport", as reported. We used electron pumping to demonstrate that high-energy, short optical pulses are not necessary to generate "laser paint" emission in powders. We also investigated strong scattering conditions to search for evidence that the onset of recurrent scattering events that begin and end on the same site facilitate laser action.