  We report room temperature lasing in two-dimensional diffractive lattices of
silver and gold plasmon particle arrays embedded in a dye-doped polymer that
acts both as waveguide and gain medium. As compared to conventional dielectric
distributed feedback lasers, a central question is how the underlying band
structure from which lasing emerges is modified by both the much stronger
scattering and the disadvantageous loss of metal. We use spectrally resolved
back-focal plane imaging to measure the wavelength- and angle dependence of
emission below and above threshold, thereby mapping the band structure. We find
that for silver particles, the band structure is strongly modified compared to
dielectric reference DFB lasers, since the strong scattering gives large stop
gaps. In contrast, gold particles scatter weakly and absorb strongly, so that
thresholds are higher, but the band structure is not strongly modified. The
experimental findings are supported by finite element and fourier modal method
calculations of the single particle scattering strength and lattice extinction.
