Person:

Russell, Kasey

Here we describe the fabrication and characterization of a plasmonic nanocavity formed in the narrow gap between a Ag nanowire and a flat Ag substrate. The fluorescence spectrum of nanocrystals within the gap was strongly modified by the cavity modes, showing peaks of position and width (Q ∼ 30–60) in quantitative agreement with numerical calculations. At gap spacings of ∼ 15 nm, the noncavity background fluorescence is largely quenched by the Ag substrate, while the modal fluorescence remains strong, indicating that gap-type structures are more robust to fluorescence quenching.

Metallic optical systems can confine light to deep subwavelength dimensions, but verifying the level of confinement at these length scales typically requires specialized techniques and equipment for probing the near field of the structure. We experimentally measured the confinement of a metal-based optical cavity by using the cavity modes themselves as a sensitive probe of the cavity characteristics. By perturbing the cavity modes with conformal dielectric layers of subnanometer thickness using atomic layer deposition, we find the exponential decay length of the modes to be less than 5% of the free-space wavelength ((\lambda)) and the mode volume to be of order (\lambda^3/1000). These results provide experimental confirmation of the deep subwavelength confinement capabilities of metal-based optical cavities.

We present a design of plasmonic cavities that consists of two sets of 1-D plasmonic crystal reflectors on a plasmonic trench waveguide. A 'reverse image mold' (RIM) technique was developed to pattern high-resolution silver trenches and to embed emitters at the cavity field maximum, and FDTD simulations were performed to analyze the frequency response of the fabricated devices. Distinct cavity modes were observed from the photoluminescence spectra of the organic dye embedded within these cavities. The cavity geometry facilitates tuning of the modes through a change in cavity dimensions. Both the design and the fabrication technique presented could be extended to making trench waveguide-based plasmonic devices and circuits.

InGaN-based active layers within microcavity resonators offer the potential of low threshold lasers in the blue spectral range. Here, we demonstrate optically pumped, room temperature lasing in high quality factor GaN microdisk cavities, containing InGaN quantum dots (QDs) with thresholds as low as (0.28 mJ/cm^2). The demonstration of lasing action from GaN microdisk cavities with QDs in the active layer, provides a critical step for the nitrides in realizing low threshold photonic devices with efficient coupling between QDs and an optical cavity.

Microdisks incorporating InGaN quantum dots were fabricated using SiO2 microspheres as a hard mask in conjunction with a photoelectrochemical etch step from a structure containing a sacrificial InGaN/InGaN superlattice. Formation of microdisks from two near-identical structures with differing dislocation densities was carried out and investigated using microphotoluminescence. This confirmed the existence of quantum dots through the presence of resolution limited spectral lines and showed a clear correlation between the resulting modes quality factors and the dislocation densities within the disks. The disks with higher dislocation densities showed up to 80% lower quality factors than the low dislocation density disks.

Cavity–emitter coupling can enable a host of potential appli- cations in quantum optics, from low-threshold lasers to brighter single-photon sources for quantum cryptography1. Although some of the first demonstrations of spontaneous emission modification occurred in metallic structures2,3, it was only after the recent demonstration of cavity quantum electrody- namics effects in dielectric optical cavities4 that metal-based optical cavities were considered for quantum optics appli- cations5–13. Advantages of metal–optical cavities include their compatibility with a large variety of emitters and their broad- band cavity spectra, which enable enhancement of spectrally broad emitters. Here, we demonstrate radiative emission rate enhancements approaching 1,000 for emitters coupled to the nanoscale gap between a silver nanowire and a silver substrate. A quantitative comparison of our results with analytical theory shows that the enhanced emission rate of gap-mode plasmons in our structures can yield high internal quantum efficiency despite the close proximity of metal surfaces.