Whispering-gallery-mode (WGM) microresonators are a promising platform for highly sensitive, label-free detection and probing of individual nano-objects. Our work expands these capabilities by providing the analysis tools required for three-dimensional (3D) characterization of arbitrarily shaped nanoparticles. Specifically, we introduce a theoretical model that describes interactions between nanoparticles and WGM resonators, taking into account effects that were often not considered, such as the elliptical polarization of the transverse-magnetic (TM) mode, the possible non-spherical shape of the nanoparticle, its finite size, and the open-system nature of the modes. We also introduce a self referencing measurement method that allows the extraction of information from measurements done at arbitrary positions of the nanoparticles within the WGM. We verify our model by experimentally probing a single Tungsten-disulfide (WS2) nanotube with a silica microtoroid resonator inside a scanning electron-microscope (SEM) and perform 3D characterization of the nanotube.
Crystals and fibers doped with rare-earth (RE) ions provide
the
basis for most of today’s solid-state optical systems, from
lasers and telecom devices to emerging potential quantum applications
such as quantum memories and optical to microwave conversion. The
two platforms, doped crystals and doped fibers, seem mutually exclusive,
each having its own strengths and limitations, the former providing
high homogeneity and coherence and the latter offering the advantages
of robust optical waveguides. Here we present a hybrid platform that
does not rely on doping but rather on coating the waveguidea
tapered silica optical fiberwith a monolayer of complexes,
each containing a single RE ion. The complexes offer an identical,
tailored environment to each ion, thus minimizing inhomogeneity and
allowing tuning of their properties to the desired application. Specifically,
we use highly luminescent Yb3+[Zn(II)MC (QXA)]
complexes, which isolate the RE ion from the environment and suppress
nonradiative decay channels. We demonstrate that the beneficial optical
transitions of the Yb3+ are retained after deposition on
the tapered fiber and observe an excited-state lifetime of over 0.9
ms, on par with state-of-the-art Yb-doped inorganic crystals.
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