CaSTL Seminar with Montacer Dridi

Abstract: We report a theoretical study of lasing when plasmonic metallic structures are embedded in a gain medium. We demonstrate theoretically and experimentally a plasmon-enhanced laser that is based on an array of gold particles that has a photonic lattice mode that is coupled to the gold nanoparticle plasmon[1]. After appropriate pumping of the gain medium, light is emitted perpendicular to the array which shows many characteristics that are expected for a laser. The theory uses a rate equation description of the gain medium, together with classical electrondynamics for the plasmonic particles, and a constitutive equation of motion for induced polarization in the molecules that is driven by the electromagnetic field of the nanoparticles. The rate equations, constitutive equations and classical electrodynamics solved together using a finite differencing algorithm. We demonstrate a coherent light emission that shows the expected threshold with pump intensity and a maximum population inversion close to the nanoparticles which is what would be expect for a plasmon-enhanced laser. The dye molecule photophysics near the nanoparticle was also studied, and it is demonstrated that stimulated emission dominates over spontaneous emission above threshold, with most of the stimulated emission being associated with the near-field region near the metal nanoparticle. The effect of nanoparticle array spacing is also studied and we theoretically demonstrate that lasing in a periodic array of gold NPs can lead to three types of lasing modes, the first being primarily local plasmonic, the second primarily photonic , and the third a hybrid mode of plasmonic and photonic components .

Based on this model, further studies should be done to explore and study the influence of geometrical parameters, quantum parameters, type of metal, and dye concentration on lasing action.

Figure 1: Plasmon-based laser: Optically pumped, 2D arrays of plasmonic Au or Ag nanoparticles surrounded by an organic gain medium were demonstrated to show directional beam emission (divergence angle <1.5° and linewidth <1.3 nm) characteristic of lasing action in the far-field, and behave as arrays of nanoscale light sources in the near-field[1].

References:

Ref1: Wei Zhou, Montacer Dridi, Jae Yong Suh, Chul Hoon Kim, Dick T. Co, Michael R. Wasielewski George C. Schatz & Teri W. Odom (2013) Lasing action in strongly coupled plasmonic nanocavity arrays. Nature Nanotechnology 8, 506–511

Ref2: Model for describing plasmon-enhanced lasers that combines rate equations with finite-difference time-domain. Montacer Dridi and George C. Schatz. JOSA B, Vol. 30, Issue 11, pp. 2791-2797 (2013)