Single- and two-photon excitation of a GaAs random laser.

We have demonstrated an anti-Stokes random laser emission at lambda approximately 885 nm in micrometer-size powder of GaAs. The maximal pumping wavelength, lambda=1,300 nm, exceeded the lasing wavelength by nearly 50%. We conclude that both one- and two-photon pumping contribute to optical excitation of the material, with the two-photon pumping being a key process in creating the population inversion and gain.

Enhancement of surface plasmons in an Ag aggregate by optical gain in a dielectric medium.

We have observed the compensation of loss in a metal by a gain in a dielectric medium in the mixture of an Ag aggregate and a Rhodamine 6G dye. The demonstrated sixfold enhancement of the Rayleigh scattering is the evidence of the enhancement of the surface-plasmon resonance. The reported experimental observation facilitates many applications of nanoplasmonics.