Abstract
We study beaming properties of laser light produced by a plasmonic lattice overlaid with organic fluorescent molecules. The crossover from spontaneous emission regime to stimulated emission regime is observed in response to increasing pump fluence. This transition is accompanied by a strong reduction of beam divergence and emission linewidth due to increased degree of spatial and temporal coherence, respectively. The feedback for the lasing signal is shown to be mainly one-dimensional due to the dipolar nature of the surface lattice resonance. Consequently, the beaming properties along x and y directions are drastically different. From the measurements, we obtain the M 2 value along both principal directions of the square lattice as a function of the pump fluence. Our work provides the first detailed analysis of the beam quality in plasmonic lattice lasers and reveals the underlying physical origin of the observed strong polarization dependent asymmetry of the lasing signal.
Highlights
Many of the appealing features of plasmonic systems stem from the high near-field enhancement and confinement of light beyond the diffraction limit [1, 2]
We study beaming properties of laser light produced by a plasmonic lattice overlaid with organic fluorescent molecules
At low pump powers (top panel of (a)), the emission of the system exhibits (1) a feature with a broad linewidth at around 844 nm, which is associated with the spontaneous emission of the IR792 dye, and (2) a second feature at 886 nm which is related to the surface lattice resonances (SLRs) of the system
Summary
Many of the appealing features of plasmonic systems stem from the high near-field enhancement and confinement of light beyond the diffraction limit [1, 2]. There exists a fundamental trade-off between the high field confinement and losses of plasmonic systems. Both ohmic and radiative losses can severely limit the applicability of plasmonic resonances. The hybridization of the lossy plasmon resonance with a low-loss diffracted orders of the lattice results in so-called surface lattice resonances (SLRs) possessing extremely narrow linewidths [12,13,14]
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