In
this article, we address subnanometer resolved fluorescence
imaging of single molecule inside a plasmonic picocavity by proposing
a semiclassical theory via combining the macroscopic quantum electrodynamics
theory and the open quantum system theory. To gain insights into the
experimental results [Nat.
Photonics202014694699], we have further equipped this theory with the classical
electromagnetic simulation of the picocavity, formed by atomistic
cluster-decorated silver STM tip and a silver substrate, and the time-dependent
density functional theory calculation of zinc phthalocyanine molecule.
Our simulations not only reproduce the fluorescence spectrum and imaging
as measured in the experiment, confirming the influence of extreme
field confinement afforded by the picocavity, but also predict Rabi
oscillation dynamics and Mollow triplets spectrum for moderate laser
excitation. Thus, our study highlights the possibility of coherently
manipulating the molecular state and exploring quantum optical phenomena
with the plasmonic picocavity.
The second harmonic generation (SHG) is systematically investigated in mechanically exfoliated, few‐layer ReS2 samples. The stacking orders are identified as (AA)nA and (ABy)nA for (2n+1)‐layer samples and (AA)n and (ABy)n for 2n‐layer samples. The layer structure A stands for that of a monolayer, and the layer structure By is mirror to A followed by a one‐tenth unit cell translation along the mirror axis, that is, the b‐axis of the crystal. Only the even‐layer samples with (ABy)n stacking order are SHG active. After carefully extracting the effective bulk susceptibility for SHG, it is found that the spectra are greatly enhanced as the fundamental photon energy matches exciton levels. The polarization dependence is strongly anisotropic, and each susceptibility component shows very different wavelength dependence. The results demonstrate that few‐layer ReS2, with its unique SHG, can be considered as an ideal platform for fundamental research in anisotropic nonlinear optics.
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