  Arrays of metallic particles patterned on a substrate have emerged as a
promising design for on-chip plasmonic lasers. In past examples of such
devices, the periodic particles provided feedback at a single resonance
wavelength, and organic dye molecules were used as the gain material. Here, we
introduce a flexible template-based fabrication method that allows a broader
design space for Ag particle-array lasers. Instead of dye molecules, we
integrate colloidal quantum dots (QDs), which offer better photostability and
wavelength tunability. Our fabrication approach also allows us to easily adjust
the refractive index of the substrate and the QD-film thickness. Exploiting
these capabilities, we demonstrate not only single-wavelength lasing but
dual-wavelength lasing via two distinct strategies. First, by using particle
arrays with rectangular lattice symmetries, we obtain feedback from two
orthogonal directions. The two output wavelengths from this laser can be
selected individually using a linear polarizer. Second, by adjusting the
QD-film thickness, we use higher-order transverse waveguide modes in the QD
film to obtain dual-wavelength lasing at normal and off-normal angles from a
symmetric square array. We thus show that our approach offers various design
possibilities to tune the laser output.
