We will present how to fabricate nanoantennas and metasurfaces in van der Waarls (vdW) materials in a variety of geometries and a range of photonic applications. We observed Mie resonances as well as strong coupling between the excitonic features and anapole modes in the vdW nanoantenna. Due to the weak vdW interactions of the nanoresonators and the substrate, we were able to use an atomic force microscopy cantilever in the repositioning of double-pillar nanoantennas to achieve ultra-small gaps of 10 nm. By employing a monolayer of WS2 as the gain material, we observe room temperature Purcell enhancement of emission as well as low temperature formation of single photon emitters with enhanced quantum efficiencies. More recently, we have also achieved bound states in the continuum ultra-low threshold lasing with these materials, highlighting the vdW materials as a promising platform for optoelectronic devices.
Hybridization between inter- and intralayer excitons can occur in Transition Metal Dichalcogenide (TMD) bilayers, giving rise to dipolar excitons with high oscillator strength. Such excitons can be exploited to achieve high optical nonlinearities, when TMDs are strongly coupled to light confined in optical microcavities. However, observations of TMD polaritons ultrafast temporal dynamics and their exploitation remain elusive. We performed pump-probe spectroscopy experiments at 8K in a custom-made microscope to study hBN-encapsulated monolayers and bilayers of MoS2 placed in optical microcavities. We probe the ultrafast dynamics of exciton-polaritons in such systems by resonantly exciting the cavities with femtosecond pulses and measuring the transient differential reflectivity. Our experiments revealed an ultrafast sub-picosecond switching from strong to weak coupling regime with a fast reversible recovery, and we demonstrated its high frequency operation (250 GHz) as an optical switch. The rich dynamics of TMD polaritons explored in our work give access to extreme nonlinear phenomena in TMD systems on ultrafast time scales for future optical logic gates.
While high index dielectrics and plasmonics offer many opportunities for research and techonology in the field of nanophotonics, 2D materials can expand this potential in the visible and near-infrared due to high refractive indices, a large range of transparency windows, and new fabrication possibilities due to van der Waals adhesion to any substrate. We extract dielectric constants of 11 layered materials including TMDs, III-VI semiconductors, and magnetics. We fabricate nanoantennas and observe Mie resonances as well as strong coupling of TMD excitons and anapole modes with Rabi splittings of 140 meV. We also observe room temperature Purcell enhancement of WSe2 monolayer emission and low temperature formation of single photon emitters with enhanced quantum efficiencies. Due to weak adhesion to the substrate, we employed an AFM tip in the repositioning of dimer nanoantennas to form ultra-small hotspots enabling optical trapping of quantum emitters with Purcell factors above 150.
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