Au nanoparticle concentration study in hybrid plasmonic microlasers

In this paper, the concentration effects of Au nanoparticles placed in dye-doped polymeric spherical microlasers are investigated. The microlasers (average diameter of ∼293µm) are made with a mixture of UV curable polymer named Norland Blocking Adhesive (NBA) and Rhodamine 6 G. Four different ratios (between the Au nanoparticles and the NBA solutions) are investigated here, namely, 1000, 2000, 3000, and 4000 ratios. The Au nanoparticles (size of ∼5nm) are randomly scattered within the microlaser. The light is collected via a multimode optical fiber, ending to a spectrometer/CCD camera. It is found that the 3000 ratio case exhibited the lowest energy threshold value and the highest photonic emission slope. The 4000 ratio (lowest concentration) exhibited a behavior that was very similar to a microlasers with no Au particles. In terms of longevity of the laser modes, the 3000 ratio case exhibited the most stable emission, although the laser mode disappeared at an earlier time. The emission of the 2000 ratio case dropped drastically after a few seconds but increased after that before dropping again; in this case, the TE and TM laser modes were found to be in competition with each other due to the partial overlapping of the plasmonic emission with some of the resonant cavity modes and due to the thermal expansion effect. The quality factor was found to be of the same order of magnitude for all cases (∼10⁴). Ultimately, this work allows us to select the optimum microlaser's configuration in terms of Au nanoparticle concentration as well as laser mode emission and longevity for different mechanical and biomedical sensing applications.