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.

We study lasing in randomized lattices of silver particles in a dye-doped waveguide. We set out to answer a basic question, triggered by earlier observations of distributed feedback lasing in 2D periodic plasmonic particle lattices: how much order do you need to obtain lasing? We start from a diffractive 2D square lattice of silver nanoparticles with a pitch that satisfies the second-order Bragg diffraction condition at the emission wavelength of the dye. By randomly removing particles and by displacing particles we increase disorder. We observe that lasing at the second-order Bragg diffraction condition is very robust, with lasing even persisting when 99% of particles are removed. Above a certain amount of disorder new features appear in the spectrum as well as in the Fourier image that are due to random lasing. We classify Fourier space output on the basis of structure factor calculations. In addition we apply speckle intensity statistics analysis to real-space fluorescence images and introduce a new method to differentiate between spontaneous emission and lasing emission.

Plasmonic particle arrays enable unconventional miniature lasers by virtue of feedback by enhanced scattering, field confinement, and diffractive resonances. Here, we demonstrate lasing in quasi-periodic and aperiodic Galois, ThueMorse, Fibonacci, paperfolding, Rudin-Shapiro, and randomized lattice arrangements of silver particles spanning the Fourier spectrum from discrete (period-like) to increasingly continuous (random-like). Through high-NA back-focal plane images we find that the laser output displays the rich Fourier spectrum of the lattice. Conversely, the real-space output at the laser plane is similar to speckle, yet with distinctly structured autocorrelations. Further, we identify many new lasing conditions on the basis of pseudo-Bragg conditions that do not occur for periodic arrays. This work enables controlled studies of lasing for any level of spatial correlation in the feedback mechanism going from periodic to random and shows that metasurface lasers offer new beam-shaping strategies.

We study lasing in distributed feedback lasers made from square lattices of silver particles in a dye-doped waveguide. We present a systematic analysis and experimental study of the band structure underlying the lasing process as a function of the detuning between the particle plasmon resonance and the lattice Bragg diffraction condition. To this end, as gain medium we use either a polymer doped with Rh6G only, or polymer doped with a pair of dyes (Rh6G and Rh700) that act as Förster energy transfer (FRET)-pair. This allows for gain respectively at 590 nm or 700 nm when pumped at 532 nm, compatible with the achievable size-tunability of silver particles embedded in the polymer. By polarization-resolved spectroscopic Fourier microscopy, we are able to observe the plasmonic/photonic band structure of the array, unravelling both the stop gap width, as well as the loss properties of the four involved bands at fixed lattice Bragg diffraction condition and as function of detuning of the plasmon resonance. To explain the measurements we derive an analytical model that sheds insights on the lasing process in plasmonic lattices, highlighting the interaction between two competing resonant processes, one localized at the particle level around the plasmon resonance, and one distributed across the lattice. Both are shown to contribute to the lasing threshold and the overall emission properties of the array.

No abstract