Recently, optical bound states in continuum (BICs) incorporated with optical gain have been reported to exhibit lasing. Here, it is shown that each of the four BICs supported by C4v$_{4v}$ symmetric photonic crystal slab can be made to lase, allowing the control over the topological charge of the resulting laser beam. The type of each BIC and their topological charges are identified by imaging the far‐field polarization vortices of the lasing signal. Results are compared with experimentally obtained dispersions, finite element method simulations, and multipole decomposition method based on the microscopic polarization currents in the photonic crystal plane. A demonstration of multimode lasing of two non‐degenerate BICs with opposite topological charges is presented. The momentum space overlap of the BICs results in a unique polarization pattern. The study provides a generalizable example for engineering the topological properties of coherent light.
We study beaming properties of laser light produced by a plasmonic lattice overlaid with organic fluorescent molecules. The crossover from spontaneous emission regime to stimulated emission regime is observed in response to increasing pump fluence. This transition is accompanied by a strong reduction of beam divergence and emission linewidth due to increased degree of spatial and temporal coherence, respectively. The feedback for the lasing signal is shown to be mainly one-dimensional due to the dipolar nature of the surface lattice resonance. Consequently, the beaming properties along x and y directions are drastically different. From the measurements, we obtain the M
2 value along both principal directions of the square lattice as a function of the pump fluence. Our work provides the first detailed analysis of the beam quality in plasmonic lattice lasers and reveals the underlying physical origin of the observed strong polarization dependent asymmetry of the lasing signal.
Investigating the behavior of analytes
at the electrode surface
is crucial in understanding the electrochemical and electrocatalytic
reactions. Although Surface Enhanced Raman Scattering (SERS) is sensitive
to minor chemical changes in the analyte, it is not widely used to
study the reaction mechanisms on nonplasmonic surfaces because of
the interference from plasmonic SERS substrates. In this study, we
have investigated the redox reaction of Nile Blue A on a glassy carbon
surface using pinhole-free silica-coated silver nanoparticles for
Raman signal enhancement. The silver nanostructures were synthesized
by a chemical reduction method, and the quality of the silica layer
was confirmed using microscopic and electrochemical method. The in situ spectroelectrochemical data reveals the catalytic
interference from silver which considerably alters the native reaction
mechanism. The pinhole-free silica layer prevents the hot electron
transfer and yields an interference-free enhancement to the Raman
signals.
We demonstrate radiation induced enhancement of both the incoupling of Raman excitation wavelength as well as Raman signal in plasmonic nanoparticle lattices. Rectangular nanoparticle lattices show two independently controllable lattice...
We demonstrate optically induced crossover from a weak to a strong coupling regime in a single photonic system consisting of propagating surface plasmon polaritons (SPPs) on a planar silver film and ultraviolet (UV)-switchable photochromic molecules. A gradual increase is observed in the vacuum Rabi splitting upon increasing UV exposure, along with intriguing behavior, where the reflectivity initially decreases due to increased losses at the weak coupling regime, and then increases due to the emergence of strongly coupled modes and the associated band gap formation at the resonance frequency of the uncoupled states. This work explicitly demonstrates the optical tunability of the degree of hybridization of the SPP and exciton modes, spanning the range from weak to intermediate and finally to the strong coupling regime.
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