Probing Temperature-Induced Plasmonic Nonlinearity: Unveiling Opto-Thermal Effects on Light Absorption and Near-Field Enhancement.

Precise measurement and control of local heating in plasmonic nanostructures are vital for diverse nanophotonic devices. Despite significant efforts, challenges in understanding temperature-induced plasmonic nonlinearity persist, particularly in light absorption and near-field enhancement due to the absence of suitable measurement techniques. This study presents an approach allowing simultaneous measurements of light absorption and near-field enhancement through angle-resolved near-field scanning optical microscopy with iterative opto-thermal analysis. We revealed gold thin films exhibit sublinear nonlinearity in near-field enhancement due to nonlinear opto-thermal effects, while light absorption shows both sublinear and superlinear behaviors at varying thicknesses. These observations align with predictions from a simple harmonic oscillation model, in which changes in damping parameters affect light absorption and field enhancement differently. The sensitivity of our method was experimentally examined by measuring the opto-thermal responses of three-dimensional nanostructure arrays. Our findings have direct implications for advancing plasmonic applications, including photocatalysis, photovoltaics, photothermal effects, and surface-enhanced Raman spectroscopy.

Substituent-Induced Hyperconjugation: Origin of the Structural Effects on the Efficiency of Photochemical Ring Opening.

Photochemical ring-opening reactions are among the most extensively employed chemical reactions in the field of chemistry. Owing to their significance, molecular-level studies of these reactions have been widely conducted. One of the major considerations in investigating the ring-opening dynamics of complex molecules on the molecular scale is the differences in dynamics between different conformers because the number of conformers arising from a specific substrate rapidly increases with the complexity of the substrate. However, to date, studies dealing with this problem have been limited to specific individual cases. That is, a rule applicable to arbitrary conformers to estimate and explain the effects of the molecular structure, such as substituents and conformations, on photochemical ring opening has not been established. Herein, we propose the concept of substituent-induced electron density leakage via hyperconjugation as a candidate for this general rule. Based on our hypothesis, we present an indicator that can predict the efficiency of the photochemical ring-opening reactions of various conformers. The relative error between the ring-opening efficiency as obtained from the indicator and that obtained from the nonadiabatic simulations was less than 25% in 56 of the 66 conformers arising from 1,3-cyclohexadiene and 12 distinct analogues. This approach offers the possibility of accurately and quickly predicting the photochemical ring-opening efficiency of arbitrary molecules in arbitrary conformations.

Defocused imaging-based quantification of plasmon-induced distortion of single emitter emission.

Optical properties of single emitters can be significantly improved through the interaction with plasmonic structures, leading to enhanced sensing and imaging capabilities. In turn, single emitters can act as sensitive probes of the local electromagnetic field surrounding plasmonic structures, furnishing fundamental insights into their physics and guiding the design of novel plasmonic devices. However, the interaction of emitters in the proximity to a plasmonic nanostructure causes distortion, which hinders precise estimation of position and polarization state and is one of the reasons why detection and quantification of molecular processes yet remain fundamentally challenging in this era of super-resolution. Here, we investigate axially defocused images of a single fluorescent emitter near metallic nanostructure, which encode emitter positions and can be acquired in the far-field with high sensitivity, while analyzing the images with pattern matching algorithm to explore emitter-localized surface plasmon interaction and retrieve information regarding emitter positions. Significant distortion in defocused images of fluorescent beads and quantum dots near nanostructure was observed and analyzed by pattern matching and finite-difference time-domain methods, which revealed that the distortion arises from the emitter interaction with nanostructure. Pattern matching algorithm was also adopted to estimate the lateral positions of a dipole that models an emitter utilizing the distorted defocused images and achieved improvement by more than 3 times over conventional diffraction-limited localization methods. The improvement by defocused imaging is expected to provide a way of enhancing reliability when using plasmonic nanostructure and diversifying strategies for various imaging and sensing modalities.

Machine learning-based leaky momentum prediction of plasmonic random nanosubstrate.

In this work, we explore the use of machine learning for constructing the leakage radiation characteristics of the bright-field images of nanoislands from surface plasmon polariton based on the plasmonic random nanosubstrate. The leakage radiation refers to a leaky wave of surface plasmon polariton (SPP) modes through a dielectric substrate which has drawn interest due to its possibility of direct visualization and analysis of SPP propagation. A fast-learning two-layer neural network has been deployed to learn and predict the relationship between the leakage radiation characteristics and the bright-field images of nanoislands utilizing a limited number of training samples. The proposed learning framework is expected to significantly simplify the process of leaky radiation image construction without the need of sophisticated equipment. Moreover, a wide range of application extensions can be anticipated for the proposed image-to-image prediction.

Plasmon-enhanced fluorescence correlation spectroscopy for super-localized detection of nanoscale subcellular dynamics.

In this report, we investigate plasmon-enhanced imaging fluorescence correlation spectroscopy (p-FCS). p-FCS takes advantage of extreme light confinement by localization at nanogap-based plasmonic nanodimer arrays (PNAs) for enhanced signal-to-noise ratio (SNR) and improved precision by registration with surface plasmon microscopy images. Theoretical results corroborate the enhancement by PNAs in the far-field. Near-field scanning optical microscopy was used to confirm near-field localization experimentally. Experimental confirmation was also conducted with fluorescent nanobeads. The concept was further applied to studying the diffusion dynamics of lysosomes in HEK293T cells stimulated by phorbol 12-myristate 13-acetate treatment. It was found that lysosomes demonstrate stronger super-diffusive behavior with relatively weaker sub-diffusion after stimulation. SNR measured of p-FCS was improved by 9.77 times over conventional FCS. This report is expected to serve as the foundation for an enhanced analytical tool to explore subcellular dynamics.

Nanoslot metasurface design and characterization for enhanced organic light-emitting diodes.

We investigate bottom-emitting organic light-emitting diodes (B-OLEDs) integrated with metasurface (MS) to analyze the effect of the structural parameters on the output performance. The performance of the MS-integrated B-OLED (MIB-OLED) is evaluated by out-coupling efficiency (OCE) and reflection of the ambient light, while attention is paid mainly to dielectric capping and metal structure of MS that may influence excitation of surface plasmon (SP). The results suggest that layer thicknesses affect the performance by as much as 10% for the OCE and up to 32% for reflectance. The OCE is in general weakly affected by the structural parameters of MS. In contrast, the reflectance characteristics are found to be dominated by localized SP that is largely determined by the length and the width of a unit slot of MS. An optimization factor introduced to evaluate the performance based on out-coupling power to the radiation mode and reflectance of MIB-OLEDs confirms that integration with MS improves performance by 16% over conventional planar structure. In particular, MIB-OLED is found to enhance OCE by 51% with Lambertian-like pattern. Enhanced performance is experimentally confirmed. The findings provide insights on how to optimize the MS structure to produce MIB-OLEDs with enhanced out-coupled power and contrast ratio.

Dispersive effects in imaging polarimetry based on a wire-grid polarizer.

We explore effects of light dispersion by a wire-grid polarizer (WGP) in imaging polarimetry. The dispersive characteristics of a WGP, combined with off-axis scene incidence, cause significant non-uniformity. The normalized performance measure of contrast due to dispersion of WGP exceeded 0.84 for transmittance and 0.90 for extinction ratio (maximum non-uniformity at 1 and 0 for uniform performance). Dispersion also produces a lateral spread in the imaging plane, which may induce spectral image misregistration. Without higher-order excitation, the misregistration can be at the least a few pixels long in the detector. In the presence of higher-order modes, the dispersive misregistration can be severe and critical for polarized scene extraction. The results emphasize the need for an imaging polarimeter to be designed to manage the dispersive effects.

Microscale heat transfer and thermal extinction of a wire-grid polarizer.

We explore heat transfer and thermal characteristics of a wire-grid polarizer (WGP) on a microscale by investigating the effect of various geometrical parameters such as wire-grid period, height, and a fill factor. The thermal properties arise from heat transfer by light absorption and conduction in wire-grids. Fill factor was found to be the most dominant geometrical parameter. For TM polarized light, a higher fill factor with thicker wire-grids increased the temperature. The local temperature was found to rise up to Tmax = 354.5 K. TE polarization tended to produce lower temperature. Thermal extinction due to polarimetric extinction by a WGP was also evaluated and highest extinction was observed to be 4.78 dB, which represents a temperature difference ΔT = 54.3 °C. We expect the results to be useful for WGPs in polarization-sensitive thermal switching applications.

Selectively bonded polymeric glaucoma drainage device for reliable regulation of intraocular pressure.

A novel glaucoma drainage device (GDD) using a polymeric micro check valve with no reverse flow is presented for the effective regulation of intraocular pressure (IOP). A significant functional improvement was achieved by reducing the possible incidence of hypotony, as the proposed GDD only drains aqueous humor at a certain cracking pressure or higher. The device consists of three biocompatible polymer layers: a top layer (cover), an intermediate layer (membrane), and a bottom layer (base plate with a cannula). All three layers, made of soft polydimethylsiloxane (PDMS), were bonded together to realize the thin GDDs. The bottom layer was selectively coated with chromium (Cr)/gold (Au) to prevent stiction between the valve seat and the valve orifice so that the device could show enhanced reliability in operation and high yield in production. Two types of polymeric devices were fabricated; one was a glaucoma drainage device for humans (GDDH) and the other was a glaucoma drainage device for animals (GDDA). From subsequent in vitro tests, the cracking pressures were 18.33 ± 0.66 mmHg (mean ± standard deviation) for GDDH and 12.42 mmHg for GDDA, both of which were very close to the corresponding normal IOPs. From in vivo tests of GDDA, the IOP of all implanted devices was properly regulated within the target pressure (10-15 mmHg). The experimental results showed that the proposed polymeric GDD has high potential for use in the treatment of glaucoma disease in terms of its repeatability of the cracking pressure and patients' relief from post-operative discomfort.