This PDF file contains the front matter associated with SPIE Proceedings Volume 11797, including the Title Page, Copyright information, and Table of Contents.

In memory of Mark Stockman

This talk will discuss current advances and future prospects in manipulating light at the nanoscale by plasmonic nanoparticle lattices. These meta-materials support collective hybrid resonances with both light scattering and localization properties. First, we will describe the expanded scope of plasmonic lattices based on exquisite tuning of topological symmetries and nanoparticle materials. Next, we will highlight how the nanoscale cavities combined with quantum emitters show unprecedented nano-lasing properties. Finally, we will discuss how this platform is opening new opportunities in imaging, strong coupling, and photoelectrocatalysis.

This Conference Presentation, “Opening Remarks and Chair Welcome,” was recorded at SPIE Optics + Photonics 2021 held in San Diego, California, United States.

This Conference Presentation, “In memorium: Mark Stockman,” was recorded at SPIE Optics + Photonics 2021 held in San Diego, California, United States.

In this talk we will highlight our most recent developments in 1) deep learning assisted optimization of photonic meta-structures and 2) machine learning-based algorithms for quantum photonic applications. We will discuss our studies on implementing deep-learning assisted topology optimization for advanced metasurface design development. We will also outline our recent work on merging topology optimization techniques with quantum device design development for achieving efficient on-chip integration. Finally, we will discuss approaches for implementing a novel convolutional neural network-based technique for real-time material defect metrology and quantum super-resolution microscopy applications.

Gratings and holograms are patterned surfaces that tailor optical signals by diffraction. Despite the long history of such structures, further advances could exploit Fourier optics, which specifies the surface pattern that generates a desired diffracted output through its Fourier transform. The required surface profile should contain a precise sum of sinusoidal waves, each with a well-defined amplitude, spatial frequency, and phase, to shape the optical wavefront. However, because fabrication techniques typically yield profiles with at most a few depth levels, complex “wavy” surfaces cannot be obtained, limiting the straightforward mathematical design and implementation of sophisticated diffractive optics. In this presentation, we will discuss a simple yet powerful approach to eliminate this design–fabrication mismatch by demonstrating optical surfaces that contain an arbitrary number of specified sinusoids.

Recent advances in wavefront shaping have led to new classes of structured light; hence, uncovering novel phenomena and facilitating new applications. We review recent progress in these areas and highlight our efforts in structuring all degrees of freedom of light; including the phase, amplitude, polarization state, and orbital angular momentum of light both in three-dimensional space and time. Notably, we showcase scenarios in which the propagation dynamics of structured vector beams are governed by a topological phase factor (i.e., the Berry phase) in addition to the regular propagation phase. This in turn redefines basic phenomena in optics encountered by these beams; such as Snell’s law, phase matching and resonance conditions. We finally present new directions in creating time-varying near-field structures using frequency-gradient plasmonic based devices.

Recently we have developed LSPR-mediated high resolution live-cell imaging techniques for adhesive cells on plasmonic metasurface composed of self-assembled gold or silver nanoparticles. Compared with other super-resolution microscopy techniques, our LSPR-mediated imaging is extremely simple but quite effective for monitoring the molecular dynamics at a nanointerface. The LSPR of the plasmonic metasurface provides high-contrast interfacial images due to the confined light within a region a few tens of nanometers from the particles and the enhancement of fluorescence. The improved lateral resolution reaches down to the theoretical limit even during cell movement due to the properties of the metasurface with an extremely high refractive index. In the presentation, we will present our latest imaging data concerning molecular dynamics in live cells, which were not visualized by other super-resolution imaging methods with low temporal resolution.

In recent years, Meta-lens has become a new type of optical device, showing excellent performance and novel applications. The nanoantennas of meta-lens can be used to control the phase, amplitude, and polarization at well. The phase part is the most important part of the function of the meta-lens. However, so far, the phase distribution of meta-lenses has not been directly measured, which further hinders the quantitative evaluation of their performance. We have developed an interferometric imaging phase measurement system for meta-lens and meta-devices. This system can measure the phase distribution by shooting the interference pattern. The phase distribution of meta-lenses can be measured to quantitatively characterize the imaging performance. Our meta-lens phase measurement system can help for designers to optimize the design, for manufacturers to identify defects, thereby improving the manufacturing process. This work will pave the way for meta-lens in industrial applications.

In this talk, I discuss our recent research activity in tailoring the scattering of nanostructures and metamaterials, with an emphasis on plasmonic phenomena. I will discuss unusual nano-optical responses associated with topological features, including embedded eigenstates, knots in the band diagram of arrays of plasmonic particles, and exotic scattering responses and absorption phenomena enabled by temporal variations. While our results in this context are mostly theoretical in nature, during the talk, I will also discuss the influence of loss and a path towards experimental verification of these concepts.

The demand for the fabrication of nanostructures consisting of metal and dielectric is increasing with the development of new plasmonic optics. Since 1997, the presenter has produced various dielectric nanostructures by the bottom-up method and reported their optical and electrochemical properties such as light propagation in two-dimensional polystyrene colloidal crystals[1], the electron emission of diamond nanorods arrays[2], photochemical micro beakers composed of TiO2[3], etc. The advantages of the bottom-up method are that you can easily try various materials in addition to being able to easily perform experiments at the laboratory level. In this presentation, we will report about the various nanostructures fabricated using thermal dewetting process of metal/dielectric interface[4], focusing on the application to the plasmonic color pigment and microfluid devices. 1 Chem. Commun. 2004, 506. 2 Chem. Lett. 2000, 29, 534. 3 Chem. Lett. 1997, 925. 4 Nanoscale Adv., 2020, 2, 2271.

Hybrid structures that combine dielectric resonators with plasmonic structures hold great promises due to the diversity of optical modes they possess. Here, we explore the physics underlying the scattering response of a hybrid nanoantenna made of a metal disk placed on top of a dielectric cylinder and study the hybridization of the different modes excited in the dielectric and metallic parts. Surprisingly, we note that the signature of an anapole state – usually only seen in high refractive index dielectrics – can be observed in the metallic part of the system. The Cartesian multipoles excited in the dielectric and metal interfere in a complex manner, leading to an unexpected high-order vector spherical multipolar response in the far-field. These effects are thoroughly studied in terms of the near-field and absorption enhancements. We also show that very fine control over the multipoles' resonant positions can be achieved by varying the geometry of the structure. This flexibility renders this system very promising for sensing applications. Based on these developments, we have designed and fabricated such hybrid nanoantennas using silicon and aluminum and measured a preliminary sensitivity of 160 nm/RIU, which is competing with conventional sensors based on localized surface plasmon resonances.

Two-Dimensional (2D) chalcogenides of Mo and W are semiconductors that show strong excitonic responses due to their highly quantum-confined character. This talk will discuss our recent work on optical phenomena and electronic phenomena in 2D semiconductors when they are placed in close proximity on plasmonic substrates such as Au, Ag and Al. I will present how 1D nanostructuring of Mos2, WS2, WSe2 etc. into nanophotonic dielectric gratings can enable exploration of new regimes of light-matter confinement including formation of hybrid exciton-plasmon-polariton states. I will extend this concept to 2D hybrid pervoskites and superlattices. Finally, I will also show how using a plasmonic tip once can use near-field tip based micro-spectroscopy to probe defects, interfaces and hybrid states in 2D excitonic semiconductors

High conductivity metals have long been the material of choice for traditional electronics, and over the past two decades low-loss metals have led to many novel optical devices and structures as a result of plasmonic confinement. As these fields merge, metal optoelectronics using hot carrier effects may pave the way for new device architectures with improved flexibility, frequency response, and ultrafast time-dynamics. In this presentation, we will discuss our recent work building hot electron photodetectors for NIR detection using Si and metal oxides, improved response using nanoscale metal alloys, and time-resolved ultrafast detection via pump-probe techniques exploiting surface plasmon excitation. Further, we will show how the incorporation of index near zero (INZ) substrates can lead to nearly 100% absorption in thin metal films, providing a new platform for hot electron devices. We will conclude with an outlook and discuss future possibilities with these novel material systems.

Due to their tunable light absorption characteristics and ability to generate hot carriers, plasmonic-metal nanostructures offer unique opportunities for light energy harnessing and conversion devices, from photodetectors to photoelectrochemical cells. In this talk I will show examples of functional devices and discuss in-depth the underlying physical mechanisms, with a special attention to the role of the metal properties. In particular, I will report recent results on ultrafast dynamics of hot holes as well as solid-state investigation of copper-based systems and I will discuss new opportunities for material synthesis and solar-energy storage applications.

Tip-enhanced Raman spectroscopy (TERS) done in ambient conditions opens the door to characterize the as-fabricated properties of nanodevices in their operating environment with both high spatial resolution and high chemical sensitivity. With sub-nanometer resolution now achievable using our TERS system in ambient, we can image nanoscale strain variations in graphene and study the strain distribution in such local domains. The effects of high photon confinement are also investigated, whose immediate manifestation is the plasmonic activation of certain Raman modes. This leads to the question of how to analyze strain at the near-field, which is quite relevant today as technology continuous to grow ever smaller.

In this work, the performance of Au/Ag nanoislands was investigated for SERS and LSPR applications. The nanoislands were generated by thermally annealing thin layers of silver and gold, which were previously sputtered onto glass surfaces. Pure metallic (silver and gold nanoparticles – AuNP and AgNP) system was evaluated based on their plasmonic and SERS sensitivity. The sensitivity of LSPR and SERS based devices are strongly depending on the used material and also on the size and geometry of the metallic nanoparticles. By controlling these parameters the plasmon absorption band can be tuned and the sensitivity can be optimized. It was found that the enhancement factor (which characterizes the increase in the peak shift for multi-particle arrangements compared to single-particle models) depends on the size of the nanoparticles and on the distance between the particles. The efficiency can be maximized by increasing the nanoisland size, and by reducing the particle distance.

Substantial effort has been invested in generating narrow bandwidth visible colors from metasurfaces using a wide variety of geometries and materials. In this work we continue these explorations and demonstrate how a combination of a plasmonic Fano resonance and a Bragg reflector can contribute to the generation of narrowband visible colors. We demonstrate active tuning of these colors by stretching the array in the x- and y- directions and the reflector in z- to shift the colorimetric response of both elements. The combination of these two types of photonic structures allows for substantially increased flexibility in design and color-space tuning. Additionally, by fabricating these structures at scale, this methodology could prove useful towards the manufacture of agile metasurface color pixels

Typically, the functionality of an optical metasurface is “hard‐coded” in its fabricated design. However, it is highly desirable to dynamically tune or even freely program the metasurface functionality also after fabrication. Recently, we have demonstrated strong active tuning of spatially homogeneous Mie‐resonant silicon metasurface by integration into nematic liquid crystal cells. This talk will review our recent advances in this field. In particular, examples of dynamic wavefront control and emission pattern tuning will be discussed. Our results can be of interest for the realization of future metasurface-based devices that can be dynamically reconfigured on demand.

In this talk, I will present two strategies to realize high-performance metasurfaces. Firstly, by introducing the generalized kerker condition to the plasmonic metasurface, we acquired a circular cross-polarization conversion efficiency higher than 50% in transmission at telecom wavelengths. We also demonstrated a couple of meta-devices with record operating efficiency based on the proposed metasurface. Secondly, I will introduce the Monte Carlo tree search (MCTS) algorithm combined with unsupervised clustering for the inverse design of metasurfaces. With the proposed method, we realized a beam steering metasurface, which is capable of deflecting normally incident light into target directions with minimal sidelobes intensity.

Band structures engineering of periodic optical structures enables the control of light propagation and localization. Although photons trapped inside 2D lattices can be described within the first Brillouin zone in reciprocal space, the wavevectors of scattered photons outside the lattice are limited by the 3D light cone, which depicts the free-photon dispersion in the surroundings. Because plasmonic nanoparticle lattices show unique dual properties of light trapping and strong scattering, this material platform is promising for investigations of radiative losses. This talk describes how light-cone surface lattice resonance (SLRs) from plasmonic nanoparticle lattices allow the observation of radiated electromagnetic fields. We theoretically predicted the angular distributions of the radiated fields, and experimentally probed the light-cone SLR modes by in-plane lasing emission. These results provide a nanolaser design strategy to achieve tunable lasing colors by lattice rotation.

A metasurface hologram combines fine spatial resolution and large viewing angles with a planar form factor and compact size. However, it suffers coherent artifacts originating from electromagnetic cross-talk between meta-atoms and nanofabrication defects. We introduce an efficient method to remove all artifacts by fine-tuning the spatial coherence of illumination. Our method is implemented with a degenerate cavity laser, which allows precise, continuous tuning of spatial coherence over a wide range with little variation in emission spectrum and total power. We find the optimal degree of spatial coherence to remove the coherent artifacts of a meta-hologram while maintaining the image sharpness.

In this report, we successfully demonstrated the room temperature operated SPP nanolaser on the graphene-insulator-metal (GIM) platform that can actively modulate the characteristics of SPP wave. The lasing threshold and emission peak of ZnO nanowire on aluminum with graphene were manipulated according to the amount of current injected to the graphene due to the nonreciprocal and thermal effect.

In this work, we will introduce our works on metal halide perovskite thin film random lasers and the latest finding of the enhanced lasing performance via in-situ AgI diffusion in perovskite materials. For the hybrid configuration, optical absorption is found to be evidently increased, indicating the availability of optical pumping fluences is prominently improved. Meanwhile, rugged film morphology and the corresponding chemical reaction are also observed and further investigated. Besides, by conducting a series of temperature-dependent cryogenic and a systematic power-dependent micro-PL measurement with different excitation wavelengths, the relationship in wavelength positions between each other can be validated, confirming the mechanism for the enhancement on light emission performance. Finally, for a such hybrid configuration, the corresponding randomlasing performance is found can be enhanced by a factor of three.

Control over the permittivity and relaxation time in materials is important to gain control over the amplitude, phase and polarization of light. In this presentation, we report our work on controlling the static and dynamic optical properties of transition metal nitrides and transparent conducting oxides for a wide array of nanophotonic applications and nonlinear optical demonstrations. We find the carrier relaxation mechanism in titanium and zirconium nitride by pump-probe studies near the ENZ. We demonstrate high-harmonic generation in refractory TiN films. We show large changes in the epsilon-near-zero points in cadmium oxide via yttrium doping, for optically controlled, mid-IR reflectance modulation. In undoped zinc oxide, we demonstrate unity-order permittivity modulation by optical doping, with 20ps response time. With TiN-AZO Berreman-metasurfaces, we demonstrate simultaneous picosecond switching at telecom wavelengths, and nanosecond switching in the visible regime. Employing the ENZ effects in aluminum-doped zinc oxide, we demonstrate nonlinear optical phenomena spanning optical time-reversal to negative refraction. Our work will aid the development of dynamic devices for a wide array of dynamic optical applications.

Nonlinear optical effects are key toward communication, sensing, imaging, etc. Recently, we found nonlinear scattering/absorption in plasmonic and silicon nanostructures based on photothermal interactions, featuring high-contrast all-optical switching and non-bleaching super-resolution microscopy. The conventional method of quantifying optical nonlinearity is z-scan, which typically works with thin films, and thus acquires ensemble nonlinear responses, not from single nanostructure. Here we advocate an x-scan technique that is based on a confocal laser scanning microscope with both forward and backward detections, offering simultaneous quantification for nonlinear behavior of scattering, absorption and total attenuation from a single nanostructure.

We will present the manifestations of plasmon-molecule energy and electron transfer processes as observed surface enhanced Raman spectroscopy (SERS). We observe that in presence of intermediary surface ligands, the electron transfer channel is turned off. On the other hand, the presence of surface ligands facilitates plasmon to molecule energy transfer (plasmon pumped adsorbate intramolecular electronic excitation) by orienting the analyte molecules along the surface field vector as well as by prolonging the excited state lifetime. The adsorbate excitation appears to be followed by singlet to triplet intersystem crossing that leads to singlet oxygen generation that initiates N-demethylation reaction as demonstrated using the reactivity of methylene.

In the weak coupling regime of light-matter interaction, the spontaneous emission of a fluorescent emitter can be tuned by placing it in a nanostructured environment such as plasmonic structures. In the strong coupling regime, the hybridization of the emitters with surface plasmons generates spatially extended coherent states called polaritons. These states span over a coherence length of several microns. We show how fluorescent quantum dots weakly coupled to a surface plasmon interact with J-aggregated organic molecules strongly coupled with a surface plasmon. We study how such interaction changes by tuning the wavelength of the quantum dots along the polariton bands.

Electrically-driven localized surface plasmon (LSP) sources is an important component for future plasmonic devices in various fields like on-chip communication and sensing. One major challenge is to incorporate small footprint, high modulation speed, and high energy efficiency into one practical system. We experimentally demonstrate a resonant inelastic electron tunneling (RIET) based LSP source working at visible and near-infrared frequencies with exceptionally high quantum efficiency. We believe this new LSP source will open up various new opportunities in plasmonic applications.

Recent progress in the fabrication of metallic thin films allows for precise control of the surface crystallographic orientation and thickness, turning them to be a great appeal in plasmonic devices. Considering such a crystalline quality and going towards smaller optical designs; surface, nonlocal, and quantum finite-size effects play a major role in metallic thin films when interacting with light. Here we explore various strategies to seek for the linear and nonlinear optical response manifested in a variety of scenarios and configurations which are based on precise quantum-mechanical formalisms that describe the dynamics of electrons in such films, e.g. EELS, Feibelman d-parameters, periodic- and finite-systems, etc. We believe that our results can inspire future devices based on crystalline metal films as well as motivate further numerical implementation strategies.

We present the band diagram analysis of a polaritonic crystal fabricated by periodically modulating the optical conductivity of a graphene sheet, which can be implemented as a virtual mirror in a Fabry-Perot type plasmonic resonator. The 2-Dimensional graphene sheet is supported by two dielectric media on top and the bottom and supports Surface Plasmon Polaritons (SPPs) at the interface. We use the Floquet-Bloch theory to write the fields in the periodically modulated structure. Using Maxwell's equations, we derive the relationship between the components of the SPP wavevector and the complex amplitude coefficients that define the linear relationship between the forward and backward propagating SPP modes. The set of nonlinear eigenvalue equations is then obtained by applying the boundary conditions at the interface. The non-retarded approximation is used to convert this to a linear eigenvalue problem. The dispersion relation is obtained by setting the determinant of the linear eigenvalue problem to zero. Band diagrams are obtained by varying the defining parameters of the Gaussian shaped periodic conductivity profile. The behaviour of the forbidden bands is then used to explain the behaviour of the SPP reflection profiles that have been observed in a recent work. The impact of the absorption losses introduced by the finite intrinsic electron relaxation time of graphene on the band structure is also analysed.

In this talk I will discuss our work on the way light confinement within plasmonic nanostructures leads to new regimes of light manipulation and control. Firstly, I will discuss the way dispersion engineering may lead to new regimes for controlling nonlinear light-material interaction, including phase mismatch-free and broadband operation. I will discuss generation of classical and quantum light in such systems. Secondly, I will highlight our theoretical works on the study of magnetized nanoplasmonic structures. Specifically, as I will demonstrate magnetization combined with the symmetry breaking naturally available in plamonic systems leads to topologically nontrivial regimes of light propagation, which is manifested in one-way propagating and rotating modes. Lastly, I will discuss our experimental work on light absorption within ultrathin film metallic nanostructures and potential applications for optoelectronics.

Tip-enhanced optical microscopy using a metallic probe has been recognized as one of the most promising applications of plasmonics. Here, we present multimodal tip-enhanced vibrational microscopy enabling to perform nanoscale Raman and IR imaging beyond the diffraction limit of light.

In this study, we demonstrate the ability to exclude the thermal effect and detect the generation of non-thermal hot carriers by surface plasmon using an AlGaN/GaN high-electron-mobility transistor. We will also provide a theoretical model to explain the detecting mechanism. This proposed platform is very sensitive, which is at least two orders of magnitude more sensitive compared to the previous reports, can detect the hot carriers generated from discrete nanostructures illuminated by a continuous wave light. The quantitative measurements of hot carrier generation also open a new way to optimize the plasmonic nanoantenna design in many applications.

We deposited niobium nitride (NbN) thin film by radio-frequency (RF) magnetron sputtering on MgO substrate at 800 ºC (with Tc ~15 K). To increase the photodetectivity, we design an Ag nanocube nanoresonator with a strong gap-plasmon resonance in the visible range to further enhance the photoresponsivity by engineering the optical response for the NbN superconducting devices. This is due to the superconducting states are broken down by a localizing strong electromagnetic field. To design the plasmonic nanostructures, we calculated the electromagnetic field distribution of Ag nanocube/Al2O3/NbN structure by finite-difference time-domain (FDTD). We observed a strong plasmonic resonance field which tightly confined in the Al2O3 layer between the Ag nanocube and NbN film at a resonant wavelength of 532 nm. In the end, we will also discuss the detailed working mechanism and the potential application of plasmon-enhanced photodetection in NbN superconducting photodetectors.

SERS has become a highly preferred method with the effect of advances in instrument technology and potential for application to many areas from medicine to art conservation for the detection of trace-level environmental and biological analytes. However, the effects of substrate variation and the details of the enhancement mechanism still of concern even much progress has been achieved in recent years. Therefore, it is important to control the size and shape of the materials for maximize the enhancement factor and ensure the reproducibility of the substrates by considering SERS uncertainty principle. In this study, we present novel SERS substrate preparation methods that are highly promising in terms of both signal enhancement and reproducibility with high benefit-cost ratio.

In this study, we experimentally demonstrate the self-assembly of gold micropetals and microfluidic control thereof using their thermoplasmonic properties. To this end, gold micropetals were fabricated on a glass substrate via glancing angle deposition and microsphere lithography techniques. Each micropetal consisted of two portions with thin gold films of different thicknesses, resulting in an intrinsic optical absorption distribution. A water vapor microbubble was generated at the region of high optical absorption of the gold micropetal immersed in degassed water via irradiation from a CW laser. Subsequently, the thickness distribution on the micropetal yielded an effective temperature gradient along the substrate surface. Resultantly, the primary water stream around the bubble was tilted by ~45° from the surface normal. The micropetal is thus shown to be useful for providing a specific temperature gradient around the microbubble and generating a flow in the desired direction under the conditions of simple laser irradiation.

Diatoms are an abundant group of algae, sharing a unique feature; they produce silica exoskeletons featuring intricate nanostructures, known as a frustule. In certain species this includes a porous network with high precision lattices, strongly resembling photonic crystals produced using modern technological processes. Here we show two means for using these frustules as an optical material. Firstly, the unprocessed frustule can be used as a conventional photonic crystal. Secondly, a metal deposition processing step can yield plasmonic crystals. Both show high quality optical properties, analogous to lab-manufactured structures, and are produced over much larger areas at a much lower cost and without specialist equipment. Optical spectra (angularly resolved dispersions) are presented, along with simulation results to corroborate experimental findings and to allow optical mode characterisation and analysis.

When graphene is placed in the near vicinity of a metal substrate, graphene plasmons are screened by the metal thereby giving rise to acoustic graphene plasmons. These exhibit record-high field confinement, squeezing light down to nanometer dimensions. Hence, plasmons in such heterostructures make ideal candidates to probe the quantum nonlocal electrodynamic response of the nearby metal. We treat graphene at the level of the RPA and describe the nonclassical optical response of the metal using a framework of mesoscopic electrodynamics based on microscopic surface-response functions, known as Feibelman d-parameters, which embody quantum corrections in the metal’s response. We show that the graphene plasmons’ resonances exhibit quantum shifts due to the quantum surface-response of the metal, and show how these spectral shifts can be used to interrogate the quantum surface-response of metals, thus provide a theoretical basis for experimentally inferring the said quantum surface-response.

We study the modification of fluorescence emission and decay rate of single fluorescent molecules in the near field of a periodic plasmonic nanostructure formed by a square lattice of Au hollow conical pillars with a periodicity of 250 nm. We perform nanometer-resolved imaging of the LDOS by simultaneously mapping the position and the decay rate of photoactivatable single-molecules with a novel super-resolved microscopy approach which enables multiplexed and super-resolved fluorescence lifetime imaging at the single-molecule level (smFLIM) with a field of view of ~10 µm2. We observe the LDOS modification of such optically rich material at different illumination conditions and we measure a large Purcell factor enhancement which increases for oblique illumination of the nanostructure.

Disorder allows us to overcome the trade-off between local enhancement of the electromagnetic field and bandwidth for plasmonic light harvesting. Here we will demonstrate a system where the spectral extent of light harvesting can be tuned via coupling a disordered plasmonic layer to an underlying Fabry-Perot cavity, allowing the transition from broadband absorption to narrow-band reflection. We examine the influence of the plasmonic material properties on the light harvesting response of our system, and demonstrate a regime where light harvesting from the far field is dominated via the interplay between the modes of the disordered system and the Fabry Perot cavity, with the actual material composition of the plasmonic layer only of secondary effect. This allows a de-coupling between the near- and the far-field response of our system: near-field enhancement in the disordered layer is dominated by the material, light-harvesting by the cavity geometry. Such a system shows promise for applications in light harvesting for energy conversion.

The signal-to-noise ratio (SNR) is the main figure of merit that assesses the quality of magnetic resonance imaging (MRI). Enhancing SNR oftentimes involves enhancing the magnetic field intensities of the constant homogenous magnetic field from the main coil, or the oscillating magnetic field from the radio frequency (RF) coil. Here we show that the SNR of MRI can also be improved by enhancing the coupling between the imaging subject and the receiving coil during the signal reception. We will provide a theoretical design of an ultrathin metasurface with micrometer thickness and high flexibility. Our metasurface can enhance the SNR by up to 28 times in the region of interest; at the same time, it is designed to minimally disturb the excitation fields by less than 1.6%, thus maintaining the uniformity of the excitation, important to achieve a high-quality MR image with minimal artifacts.

This talk will review our recent studies on the nonlinear and emission properties of conducting oxide and metallic nitride epsilon-near-zero (ENZ) materials. I will present a method to engineer the field intensity enhancement of the Al-doped zinc oxide (AZO) ENZ thin films synthesized by atomic layer deposition (ALD) technique. I will then discuss the observation of abnormal nonlinear temporal dynamic of hot electrons and enhanced optical nonlinearity in AZO and ITO ENZ thin films under different pump fluences and excitation angles using a degenerate pump-probe spectroscopy technique. Finally, I will present the first comprehensive study of photoluminescence from a 2D material placed near ENZ films and its dependence on the losses of materials, as well as the spectral response of such emitters with excitation wavelengths across the ENZ regime. This work was supported in part by the National Science Foundation (grant number: 1752295) and AFOSR-AOARD (FA2386-18-1-4099)

Here, we will report our recent results on plasmon-enhanced nonlinear optical responses in two-dimensional monolayer materials (with the enhancement factor up to three-order of magnitude with a wide operation bandwidth). Such a significant and wideband enhancement can be well explained by the highly localized field in the plasmonic structures, which is interesting for various nonlinear photonic and optoelectronic applications.

When a monochromatic electromagnetic plane-wave arrives at the flat interface between its transparent host (i.e., the incidence medium) and an amplifying (or gainy) second medium, the incident beam splits into a reflected wave and a transmitted wave. In general, there is a sign ambiguity in connection with the 𝑘-vector of the transmitted beam, which requires at the outset that one decide whether the transmitted beam should grow or decay as it recedes from the interface. The question has been posed and addressed most prominently in the context of incidence at large angles from a dielectric medium of high refractive index onto a gain medium of lower refractive index. Here, the relevant sign of the transmitted 𝑘-vector determines whether the evanescent-like waves within the gain medium exponentially grow or decay away from the interface. We examine this and related problems in a more general setting, where the incident beam is taken to be a finite-duration wavepacket whose footprint in the interfacial plane has a finite width. Cases of reflection from and transmission through a gainy slab of finite-thickness as well as those associated with a semi-infinite gain medium will be considered. The broadness of the spatio-temporal spectrum of our incident wavepacket demands that we develop a general strategy for deciding the signs of all the 𝑘-vectors that enter the gain medium. Such a strategy emerges from a consideration of the causality constraint that is naturally imposed on both the reflected and transmitted wavepackets.

Organic semiconductors are commonly used for the development optoelectronic devices. However, these materials degrade rapidly in the presence of light and oxygen. we expand upon our previously methods of using thin metal films to enhance the stability of a polymer via metal enhanced fluorescence. When overlap of the plasmon peak and peak fluorescence of the polymer is achieved the radiative decay rate increases. The plasmon can be tuned via changing the deposition time and current settings of the sputter coater used for coating. By obtaining fluorescence images of the polymer deposited on the metal film compare to on glass in ambient air, a high degree of stabilization is found via plasmonic interactions. Lifetimes were also obtained of the polymer on glass, an electron transporting layer, and a gold film to compare the changes in lifetime from plasmonic interactions versus charge transfer. The usefulness of plasmonic for organic solar cell materials was probed in this way.

We have studied the effects of planar, lamellar, and random nanostructured metal-dielectric environments on spontaneous emission and energy transfer concentration quenching of HITC laser dye. We found an inhibition of the concentration quenching in vicinity of metal, which was stronger in nanostructured substrates than in plain geometries. It was shown that the same substrates, which boosted spontaneous emission, also inhibited the concentration quenching. The effect is discussed in terms of the Förster radius affected by losses. Work at LLNL was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344

In this work, we performed a systematic study on a hybrid plasmonic system to elucidate a new insight into the mechanisms governing the fluorescent enhancement process. We have used hyperbolic meta-antennas to study the emission properties of CdSe/ZnS quantum dots (QDs). By introducing a dielectric layer inside the plasmonics antenna we engineer the absorption and scattering spectrum. Our lithographically defined meta-antennas with various diameters act as receiver and transmitter nano-antennas to outcouple efficiently the photoluminescence of the QDs.

Exploring exciton-polariton effects in low dimensional semiconductors with large oscillation strength provides solutions to develop low threshold lasers and low-energy consumption, fast photonic interconnections. In this talk, I will introduce our recent results on surface plasmon enhanced exciton-polariton of perovskite nanowires. We find that Rabi splitting energy of MAPbBr3 nanowires is enhanced by 40% by adopting a semiconductor nanwire/dielectric/Ag film sandwich structure. A Rabi splitting energy up to 595 meV is achieved as the dielectric thickness is 5 nm. Later, we demonstrated a room temperature, low-threshold green plasmonic laser in the same configuration.

We developed two-dimensional arrays of larger plasmonic metal nanoparticles than before by employing bottom up methods and investigated their plasmonic properties for sensing and photoelectrochemical applications. From surface enhanced Raman scattering (SERS) measurements, we found that the array consisting of gold nanoparticles with the diameter of 50 nm exhibited larger enhancement effects than that of 15 nm.

The theory of eigenstates of Maxwell's equations in a composite medium is extended to composites that have many constituents where every constituent can have arbitrary but uniform values of the dielectric constant, the electric conductivity and the magnetic permeability. Those eigenstates are then used to develop an expansion for the local physical electric field which results either from a given electric current distribution or a given “incident field", which means a field that is produced in the pure “host constituent" that is the only constituent which extends out to infinite distances.

In this conference, I will brie y introduce the theories of resonance energy transfer and molecular fluorescence coupled to plasmon polaritons from weak to strong light-molecule couplings (i.e., from the Franck-Condon to polariton regime). Based on macroscopic quantum electrodynamics, our theories can model hybrid light-molecule states in dispersive and absorptive (lossy) linear dielectrics. In other words, our theory can estimate the light molecule coupling and dielectric loss without any free parameters. In addition, the simulations of quantum dynamics of hybrid light-molecule states and the corresponding numerical scheme will be presented. Finally, I will demonstrate how hybrid light-molecule states are influenced by the interplay between the light-molecule coupling and the vibronic coupling.

We present a sub-wavelength-scale plasmomechanical system consisting of an Au/hydrogen silsesquioxane (HSQ) plasmonic nano-resonator and a supporting HSQ nano-wall. The full footprint of the system in three dimensions is only ~0.15 μm^3, which is just ~0.59 times of cubic wavelength. Strong optical scattering and dissipation of plasmonic resonance enable interaction with mechanical motion. We experimentally demonstrate the optical excitation and readout of the fundamental longitudinal mechanical oscillation, of which the real displacement is in the order of pico-meter. The plasmonic resonance with a wide spectral width allows the optical measurement of the mechanical oscillation signal over a large wavelength range (>100 nm) of the probe laser. Our dissipatively coupled plasmomechanical system shows not only tunability of the resonance frequency of mechanical oscillation but also the thermoelastic damping effect on the mechanical quality factor depending on the pump laser power.

In this work we propose the use of self-assembled CdZnO nanoparticles as a route to improve power absorption in midinfrared GaAs-based quantum well infrared photodetectors (QWIPs). We experimentally demonstrate low temperature growth of CdZnO nanoparticles on GaAs and characterize their plasmonic response in the mid-IR. Computational analysis of the plasmonic resonances coupled to intersubband transitions in GaAs quantum wells show that intersubband absorption at normal incidence, forbidden by quantum selection rules, can be obtained. Gains in the quantum well power absorption as high as 5.5 are also reported.

An optical metasurface may be modeled using boundary conditions that relate the fields interacting with it to the response of its scattering particles usually expressed in terms of electric and magnetic dipolar responses. Additionally, these boundary conditions also typically account for weak spatial dispersion, such as bianisotropy, to properly model effects like chirality. While such modeling approaches are sufficient for operations in the paraxial limit, they usually fail when larger angles of propagation or electrically large scattering particles are considered. To overcome these limitations, we derive boundary conditions that include dipolar and quadrupolar responses and higher-order spatially dispersive effects and show in which situations they can be useful. Since, this approach requires the introduction of many new effective material parameters in the form of hypersusceptibilities, we also provide an extension to the Lorentz reciprocity and Poynting theorems.

Currently, there are no cheap and compact sources in the mid-infrared range that can be modulated at high frequencies. Incandescent sources such as hot membranes and globars are widely used for mid-infrared spectroscopic applications, but for detection or communication applications where fast temperature modulation are desirable, thermal inertia quickly becomes a limiting factor. Besides, such incandescent sources are typically unpolarized, isotropic, broadband and have a low efficiency. However, these properties are not imposed by fundamental limitations stemming from physics laws, except for the low brightness dictated by Bose-Einstein distribution. Here, we introduce a metasurface that combines nanoscale heaters to ensure fast thermal response and nanophotonic resonances to provide large spectrally selective and polarized emissivity. We report a peak emissivity of 0.8 and an operation up to 20 MHz, six orders of magnitude faster than commercially available hot membranes.

Temperature gradient across a thermoelectric device is a keystone to generate electricity based on Seebeck effect. Here, we propose a metamaterial thermoelectric device that is able to generate electricity even under homogeneous temperature environment. Metamaterial perfect absorber fabricated on a thermoelectric device electrode absorbs thermal radiation emitted from the surrounding environment, resulting in a generation of local heating. The local heating propagates to the underneath thermoelectric device through a metal electrode, resulting in an additional thermal gradient across the device. We examined the metamaterial thermoelectric device performance put in a homogeneous temperature environment at 423 K and found that an additional thermal gradient of 0.5 K is added to the bismuth telluride thermoelectric device.

The electromagnetic modes of a sub-wavelength sized antenna can be excited both optically and through thermal fluctuations. When dealing with individual or a small number of nano-antennas, highly sensitive techniques, such as thermal radiation scanning tunneling microscopy, and infrared spatial modulation spectroscopy, are required in order to extract the very weak emitted thermal radiation. Using these techniques, we have been able to characterize the thermal emission of a single pair of sub-λ metal-insulator-metal antennas separated by a nanometric gap. It is found that the various hybrid modes of a single antenna pair can be simultaneously excited by thermal fluctuations, an essentially incoherent process arising from fluctuating thermal currents. The effect of hybrid plasmonic modes on the resonant behavior of the considered antenna system may guide future efforts for realizing tunable optical and thermal structures made up of a small number of antennas, for various applications.

Highly sensitive thermometric methods are essential to the evaluation of nanoplatforms for thermal applications. In this study, the dual-beam thermal lens technique was introduced to assess the optically induced temperature changes in colloidal samples of gold nanoparticles. Dual-beam measurements were performed on a 0.05 mg/mL gold nanospheres (50 nm diameter) aqueous solution and the localized nanoparticle temperature were determined. The system was able to detect temperature variations as low as 10^-2 °C, with 0.2 °C^-1 sensitivity in the assessment of metallic nanoparticle colloids. Furthermore, thermal lens measurements also allowed the acquisition of the nanoparticle absorption cross-section value, regardless of its scattering properties.

The complex Ag nanohole structures with an Ag nanorod inside the hole are designed and investigated both numerically and experimentally. Based on finite-difference-time-domain (FDTD) calculations, these structures show strong polarization angle-dependent optical properties. Additionally, a new extraordinary optical transmission (EOT) mode with tunable resonance wavelength is observed at the near-IR region due to the enhanced local radiation of the nanorods as well as electromagnetic coupling to the nanoholes. The resonance wavelength of the new EOT mode can be red-shifted continuously from the near-IR region to the mid-IR region (~ 20μm ) by varying array periodicity and nanorod length. By combining nanosphere lithography with oblique angle deposition, large-area Ag nanorod in nanohole structures can be fabricated on glass substrates. This fabrication technique enables the production of the complex nanohole arrays with controlled hole diameter, thickness, and rod structure inside the hole. The observed transmission at the new EOT mode can increase from ~41% of the nanohole to ~78% of the compound structure. The tunable EOT wavelength and strong polarization-dependent optical properties make the structure ideal for applications such as ultrathin optical filters, polarizers, surface-enhanced spectroscopies, etc.

Plasmonic materials are well stablished and used in fields like biomedicine or energy harvesting due to their exceptional optical properties. One of the most interesting characteristics of plasmonic nanoparticles is their ability to confine light at the nanoscale. Nevertheless, such behaviour can also be found in some non-metallic materials as in organic-excitonic materials based on J-aggregates. Herein, we evaluate the synthetic route to obtain colloidal dispersions of excitonic core-shell nanoparticles that can mimicking plasmonic behaviour.

The quantification of the spectral variation in optical properties, such as absorption and scattering cross-sections, of gold nanorods (GNRs) present within a medium is important for various applications such as spectroscopy, sensing and biomedical applications. The calculated absorption cross-section helps in the estimation of the plasmonic response of GNR, which is suitable for heat generation within a medium during the interaction of electromagnetic fields with nanoparticles. Here, the optical properties of GNR are simulated by using the finite element method and the role of domain size is evaluated. The domain is finer meshed by using tetrahedral elements of size range 0.48 – 60 nm, curvature factor of 0.7 and maximum element growth of 1.40. The electric field distribution is estimated by considering the propagation direction along the x-axis with incident field vectors along z-axis. The discussed results indicate that, on increasing the size of domain (medium) surrounding the GNR from 50 nm to 200 nm, the optical absorption cross-section increases by 450 nm², and scattering cross-section decreases by 190 nm². Also, the plasmonic wavelength of GNR gets blue-shifted, and the full-width half maxima (FWHM) gets decreased with an increase in the domain size. So, for the evaluation of the optical properties of GNR in a medium using the FEM model, the selection of domain diameter plays a significant role. Also, this quantitative knowledge of the role of a domain size will be useful for an estimation of the electric field distribution in a medium.

Mid-wavelength infrared (MWIR, λ = 3 – 5 μm) materials are of great importance due to their applications in optical sensors and devices for military, industry, and non-invasive medical diagnostics. Specifically, MWIR polarimetry are used in biometric recognition and camouflaged detection. Recently, sulfur based organically modified chalcogenides (ORMOCHALC) polymers have been utilized to fabricate MWIR polarizers with competitive extinction coefficient to commercial polarizers, which are mostly made of expensive, brittle, and heavy inorganic materials. On the other hand, to adjust or reinforce the refractive index of the polymer, the chalcogenide content (i.e., sulfur, selenium) needs to be increased, which may result in adverse effects on the thermomechanical characteristics, including Young's modulus and lower glass transition temperature. This reduced thermomechanical stability compromises the structural integrity of ORMOCHALC-based optical devices. In this study, an ORMOCHALC polymer, poly(S–r–DIB), was reinforced with the zinc sulfide (ZnS) nanoparticles to simultaneously improve the refractive index and the thermomechanical properties. The addition of 20 wt% ZnS nanoparticles improves the pure polymer's glass transition temperature (T_g) from 9.6 °C to 31.4 °C, and the refractive index by Δn= 6.58 %. Then, subwavelength wire-grid polarizers were fabricated based on the pure ORMOCHALC first by a simple thermal imprinting method followed by metal deposition. The resulted MWIR polarizer showed a high extinction coefficient which is comparable with commercial polarizers. However, the structural integrity of the polarizers was compromised due to lower glass transition temperature. Finally, finite element analysis was conducted on the possible wire-grid polarizer fabrication utilizing optically and mechanically reinforced composites, as demonstrated in this study. If fabricated, these nanoparticles reinforced polarizers will possess superior structural integrity compared to ORMOCHALC polarizers. Moreover, these polarizers show a spectral selectivity as the transmission curve's resonance wavelength depends on the composite's refractive index, which is tunable by controlling the nanoparticles content. The resonance peak redshifted from 3.12 μm to 3.3 μm for the pure polymer to 20% ZnS reinforced ORMOCHALC polarizer. The extinction coefficient of the polarizer also improved in multiple wavelength bands in the MWIR. These polarizers with superior extinction coefficient, spectral selectivity, and improved thermomechanical stability demonstrate a broader prospect in MWIR optics.

We investigate spatial control of femtosecond surface plasmon polariton wave packets (SPP WPs) induced by a nanoscaled metal-insulator-metal structure by using time-resolved two-photon excitation microscopy and numerical calculations. Irradiations of 10 fs laser pulses to a ridge structure placed on a Au film launch SPP WPs that propagate on the surface to interact with a MIM nano-cavity. When the SPP WP reaches the MIM nano-cavity, the field intensity of the WP of which frequency coincides with the cavity resonance is enhanced in the MIM structure, and then transmits the cavity to continue the propagation. The time-resolved micrographs reveal deformations of the spatial shape of WPs after passing through the cavity. Because the SPP WP possesses a down-chirped spatial frequency while propagating on the Au surface, the spectral modulation of the WP owing to the cavity transmission is reflected as a spatial deformation of the envelope shape. When the cavity transmits low (high)-frequency components, the peak position of the transmitted WPs shows an advance (delay) sift compared to a reference WP propagated on the plane surface. The numerical model based on complex dispersion relations of the SPP reasonably reproduced the deformation of the SPP WP.

Metasurface enables controlling the light properties at will by structuring sub-wavelength unit elements. Among feasible applications, polarization control plays a vital role in communication, quantum optics, and imaging. Due to the Joule loss issue, the polarization conversion efficiency for the plasmonic metasurfaces operating at NIR region is usually lower than 10% [1]. In this work, we innovate a metasurface design to enhance the polarization conversion efficiency [2]. A S-shaped plasmonic metasurface with a toroidal dipole-quadrupole coupling response is used to push the polarization conversion efficiency to 22.9% that is very close to the theoretical conversion limit 25% [3].

Large-area plasmonic metasurfaces have attracted interest as potential tools for a wide range of applications, from colorchanging glass to improved efficiency of solar cells. These potential applications necessitate the capability to fabricate such surfaces at scale. One potential approach to resolve this issue is to use nanoimprint lithography to mold a metasurface structure and then use chemically synthesized nanoparticles as the metallic elements. By combining aluminum nanoparticles with electrophoretic deposition, a low-cost method of scalable fabrication could be achieved.

Plasmonics has opened unforeseen applications due to its sub-wavelength scale control over modes of collective oscillations of free electron gas in solids. This control is only possible due to nano-structuring of the underlying media. I introduce my TeraVolts per meter (TVm⁻¹) plasmonics initiative which promises many tens of TVm⁻¹ fields by relying on nanostructured materials to access a novel class of relativistic plasmonic modes excited as “trailing wake” of intense ultrashort particle bunches. Nanomaterial tubes with a hollow core are critical to mitigate the disruptive effects of collision of the particle beam with the ionic-lattice. Specifically, I present underlying concepts and theoretical model of highly nonlinear surface plasmonic waves. These surface waves are sustained by a train of “crunch-in” surface plasmons with large-scale electron-ion charge-separation which leads to tens of TVm⁻¹ fields. The crunch-in surface plasmons are thus strongly electrostatic unlike other plasmonic modes. Access to unprecedented plasmonic fields opens far-reaching possibilities for transformative impact.

The goal of this study is development of ultra-sensitive and reproducible SERS platform based on novel magnetoplasmonic nanoparticles produced by laser ablation. The magnetic part of hybrid nanoparticles ensures manipulation of the nanoparticles by magnetic field by arranging them at biological surfaces in a special geometry resulting in high and reproducible SERS. Magneto-plasmonic Au-Fe nanoparticles in colloidal suspension were prepared by picosecond laser ablation of evaporated iron and gold films on glass. The nanoparticles were characterized by UV-visible extinction, high resolution electronic microscopy, and Raman spectroscopy. EDX analysis revealed that the shell of nanoparticles (2−20 nm) consist of iron and the core is composed mostly of gold. The plasmonic behavior of nanoparticles was accessed by analysis of SERS spectra from adsorbed adenine as probe ligand. The fabrication of hybrid nanoparticles by laser ablation offers a new possibility for construction of SERS substrates with tunable optical and magnetic properties for biomedical sensing.

Nanoscale molecular clusters are fascinating fluorescent nanomaterials formed by highly ordered assembly of organic dyes with the optical properties strongly different from those of monomolecules. Hybrid films formed by pseudoisocyanine dye coated metal nanoparticles on a sapphire substrate or nanoporous alumina on an aluminum substrate were studied with steady‐state and time-resolved spectroscopy. On-surface reaction caused isomerization of cyanine molecules as well as self-assembly into molecular nanoclusters, so called J‐aggregates. The excitonic band of clusters had been strongly coupled to plasmonic response of metal nanoparticles. The dynamics of the strong coupling regime was directly analyzed depending on environmental conditions (temperature and presence of gas analyte). The energy transfer of the optical excitation from oxygen vacancies of alumina to the molecular clusters was observed depending on the anodization conditions of the aluminum substrate. Such unique feature should provide a new approach to develop new sensors.

Pulsed electron beam sources are increasingly in demand, especially as probes for ultrafast science and as patterning tools in lithography applications. Plasmonic nanostructures have been shown to enhance multiphoton photocurrent from metal cathodes by orders of magnitude, but for many applications it is also important to characterize the transverse electron beam properties. Here, we present preliminary work demonstrating a DC photogun setup for characterizing plasmonic photoemitters at Lawrence Berkeley National Laboratory, including measurement of photocurrent and the asymmetric transverse phase space of photoemitted beams from plasmonic nanogroove resonator arrays. This lays the groundwork for future studies of emerging plasmon-enhanced photoemitter designs, such as plasmonic lens nanoemitters.