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1. Emission of R6G dye in Fabry–Perot cavities in weak and strong coupling regimes

   https://doi.org/10.1364/JOSAB.403612  

   Faruk, Md_Omar ; Jerop, Nelly ; Noginov, Mikhail_A ( October 2020 , Journal of the Optical Society of America B)

   We have studied spectra and angular distribution of emission in Fabry–Perot cavities formed by two silver mirrors separated by a layer of poly (methyl methacrylate) polymer doped with rhodamine 6G (R6G) dye in low ($20\mathrm{g}/\mathrm{l}$) and high ($200\mathrm{g}/\mathrm{l}$) concentrations. The frequency of emission radiated to a cavity mode was larger at large outcoupling angles—the “rainbow” effect. At the same time, the angle of the strongest emission was also determined by the cavity size: the larger the cavity, the larger the angle. The angular distribution of emission is commonly dominated by two symmetrical lobes (located at the intersection of the three-dimensional emission cone with a horizontal plane) pointing to the left and to the right of the normal to the sample. Despite the strong Stokes shift in R6G dye, the branch of the cavity dispersion curve obtained in the emission experiment is positioned above the one obtained in the reflection (extinction) experiment. Some dye molecules are poorly coupled to cavity modes. Their emission has very broad angular distribution with the maximum at$\mathrm{\theta <\#comment/>}=0^{\circ <\#comment/>}$. The signatures of strong cavity–exciton coupling were observed at high dye concentration ($200\mathrm{g}/\mathrm{l}$) but not at low concentration ($20\mathrm{g}/\mathrm{l}$). The evidence of the effect of strong coupling on emission is exemplified by a strong difference in the angular distribution of emission in two almost identical cavities, one with and another without strong coupling. Most importantly, we have demonstrated the possibility to control the ground state concentration, the coupling strength, and the dye emission spectra with Q-switched laser pulses.

    

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2. Energy Transfer for Leaky Surface Plasmon Polaritons in Gold Nanostripes

   https://doi.org/10.1021/acs.jpcc.4c08238  

   Bhandari, Janak ; Hartland, Gregory V ( January 2025 , The Journal of Physical Chemistry C)

   The properties of the leaky surface plasmon polariton (SPP) modes in gold nanostripes were investigated using scattered light microscopy. Both bare gold nanostripes and stripes coated with a thin polymer film containing a near-infrared absorbing dye were examined. Real-space microscopy images were employed to determine the SPP propagation length, while Fourier space images provided measurements of the wavevector. Frequency versus wavevector dispersion curves were generated by performing experiments at different excitation wavelengths, and the slopes of these curves yielded the SPP group velocities. For the bare nanostripes the group velocity was determined to be vg = (0.92 ± 0.05)c0 and for the dye-coated nanostripes it was vg = (0.85 ± 0.06)c0, where c0 is the speed of light. The SPP lifetimes were estimated by combining the group velocity and propagation length measurements. The results show that the lifetime of the gold SPPs is significantly reduced when the nanostripes are coated with the dye. At the peak of the dye absorption curve the change in the SPP dephasing rate induced by the dye–polymer film was found to be 0.07 fs–1. Finite element simulations show that the increased dephasing is due to a combination of energy transfer from the SPP modes to the dye, as well as increased radiation damping due to changes in the dielectric environment of the nanostructures. These findings provide insights into the energy transfer processes in plasmonic systems, which can be leveraged to optimize the design of plasmonic devices for applications in sensing, imaging and nanophotonic circuits. 

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3. Anomalous dips in reflection spectra of optical polymers deposited on plasmonic metals

   https://doi.org/10.1515/nanoph-2022-0450  

   Shorter, Ayanna ; Chowdhury, Md Golam ; Rout, Sangeeta ; Noginov, Mikhail A. ( January 2023 , Nanophotonics)

   Abstract We have studied reflection spectra of dye-doped and undoped polymers deposited onto Ag and Au substrates and found anomalous dips in the UV spectral range. On top of Ag substrates, the λ ∼ 375 nm dips were observed in undoped PMMA, PVP, and PS polymers as well as PMMA doped with Rh590 and HITC laser dyes. In silver-based samples, the spectral positions of the observed reflection dips were close to singularities in the refractive indexes of surface plasmon polaritons (SPPs) propagating at the interface between Ag and polymer. The latter singularities can tentatively explain the λ ∼ 375 nm reflection dips, if the scattering of Ag and polymeric films is large enough to launch SPP without any prism or grating. The dips observed in reflection of Rh590:PMMA and HITC:PMMA on top of Au, were more pronounced than those on Ag, broader, shifted to shorter wavelengths, and their spectral positions had large standard deviations. Furthermore, no anomalous dips in gold-based samples were observed in the reflection spectra of undoped PMMA, PVP, and PS polymers, and a modest singularity in the SPP refractive index, predicted theoretically at λ ∼ 500 nm, cannot explain the dips in the UV reflection spectra observed experimentally. It appears likely that the origin of the reflection dips on top of Au substrates is different from that on top of Ag substrates. 

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4. Emission kinetics of HITC laser dye on top of arrays of Ag nanowires

   https://doi.org/10.1515/nanoph-2021-0374  

   Rout, Sangeeta ; Peters, Vanessa N. ; Pradhan, Sangram K. ; Bonner, Carl E. ; Noginov, Mikhail A. ( October 2021 , Nanophotonics)

   Abstract We have grown arrays of silver nanowires in pores of anodic alumina membranes (metamaterials with hyperbolic dispersion at λ  ≥ 615 nm), spin coated them with the dye-doped polymer (HITC:PMMA), and studied the rates of radiative and nonradiative relaxation as well as the concentration quenching (Förster energy transfer to acceptors). The results were compared to those obtained on top of planar Ag films and glass (control samples). The strong spatial inhomogeneity of emission kinetics recorded in different spots across the sample and strong inhibition of the concentration quenching in arrays of Ag nanowires are among the most significant findings of this study. 

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5. Lateral dispersion of dye and drifters in the center of a very large lake

   https://doi.org/10.1002/lno.11302  

   Choi, Jun ; Troy, Cary ; Hawley, Nathan ; McCormick, Michael ; Wells, Mathew ( August 2019 , Limnology and Oceanography)

   To better understand lateral dispersion of buoyant and nonbuoyant pollutants within the surface waters of large lakes, two lateral dispersion experiments were carried out in Lake Michigan during the stratified period: (1) a dye tracking experiment lasting 1 d; and (2) a drifter tracking experiment lasting 24 d. Both the dye patch and drifters were surface‐released at the center of Lake Michigan's southern basin. Near‐surface shear induced by near‐inertial Poincaré waves partially explains elevated dye dispersion rates (1.5–4.2 m²s⁻¹). During the largely windless first 5 d of the drifter release, the drifters exhibited nearly scale‐independent dispersion (K ∼ L^0.2), with an average dispersion coefficient of 0.14 m²s⁻¹. Scale‐dependent drifter dispersion ensued after 5 d, withK ∼ L^1.09and corresponding dispersion coefficients of 0.3–2.0 m²s⁻¹for length scalesL= 1500–8000 m. The largest drifter dispersion rates were found to be associated with lateral shear‐induced spreading along a thermal front. Comparisons with other systems show a wide range of spreading rates for large lakes, and larger rates in both the ocean and the Gulf of Mexico, which may be caused by the relative absence of submesoscale processes in offshore Lake Michigan.

    

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