Colloidal Quantum Dot Spasers and Plasmonic Amplifiers

Surface-plasmon polaritons (or plasmons for short) are electromagnetic waves with both electronic and photonic character. In contrast to photons, plasmons can be focused to the nanoscale, enabling miniaturized devices for information and sensor technologies. Unfortunately, plasmons suffer from significant intrinsic losses, and strategies to amplify plasmonic signals have been sought. This has led to plasmonic lasers, or “spasers,” devices that actively generate plasmons of high intensity. However, because previous spaser efforts aimed primarily at obtaining the smallest possible laser, their designs were ill-suited for integration with other elements in a larger plasmonic circuit, limiting their use. We will discuss a versatile class of quantum-dot-based spasers whose design allows for the controlled on-chip generation, extraction, and manipulation of plasmons. By lithographically defining block reflectors on ultrasmooth silver via template stripping [1], we fabricate stable, aberration-corrected plasmonic cavities with high quality factors (Q) at desired locations on a substrate. We then incorporate colloidal quantum dots into these cavities with electrohydrodynamic printing [2,3] or simple large-area drop-casting. Above low excitation thresholds, monochromatic plasmons (0.65 nm linewidth at 630 nm; Q ≈ 1000) that match cavity modes are produced under ambient conditions [4]. This spaser signal is then extracted, directed through an integrated amplifier, and focused at a nearby tip, generating intense electromagnetic fields. More generally, our device platform can be deployed at different wavelengths, size scales, and geometries on large-area plasmonic chips for fundamental studies and applications.
References
[1]    P. Nagpal, N. C. Lindquist, S. H. Oh, D. J. Norris, Science 325, 594 (2009).
[2]    P. Galliker, J. Schneider, H. Eghlidi, S. Kress, V. Sandoghdar, D. Poulikakos, Nat. Commun. 3, 890 (2012).
[3]    S. J. P. Kress, P. Richner, S. V. Jayanti, P. Galliker, D. K. Kim, D. Poulikakos, D. J. Norris, Nano Lett. 14, 5827 (2014).
[4]    S. J. P. Kress, J. Cui, P. Rohner, D. K. Kim, F. V. Antolinez, K.-A. Zaininger, S. V. Jayanti, P. Richner, K. M. McPeak, D. Poulikakos, D. J. Norris, Sci. Adv. 3, e1700688 (2017).