This PDF file contains the front matter associated with SPIE Proceedings Volume 11904, including the Title Page, Copyright information, and Table of Contents.

Two-dimensional transition metal dichalcogenides (TMDs) exhibit remarkable optical properties. However, their applications in electronics and photonics are severely limited by the intrinsically low absorption and emission rates. Due to the strong local-field enhancement effect, plasmonic nanostructures are regarded as the ideal platform to enhance the photoluminescence (PL) of TMDs. To obtain a giant PL intensity, it is indispensable to apply plasmonic nanocavity with multiple resonances to simultaneously enhance the absorption at the excitation wavelength and boost the radiative rate at the emission wavelength. However, few works take the advantages of the multiple resonances in the nanocavity to augment both the PL absorption and emission processes. Here, we propose a silver (Ag) nanowire-on-mirror (NWoM) nanocavity and demonstrate the PL enhancement of monolayer MoSe₂ using the multiple resonances of the nanocavity. By carefully designing the NWoM structure, we observe the Fano resonance resulted from the coherent interaction between the discrete exciton state of monolayer MoSe₂ and the broadband plasmon mode. The Fano resonance, as a characteristic of the moderated coupling between plasmon and exciton, shows a remarkable ability of boosting the emission rate of the hybrid system utmost. Meanwhile, we align another resonance of NWoM nanocavity at the excitation wavelength to enhance the absorption of monolayer MoSe₂. This good spectral overlap is accompanied with an excellent spatial overlap between the distributions of excitation and emission enhancement within the nanocavity that allows to observe an over 1800-fold enhancement of the PL intensity.

Perfect optical vortices (POVs), consists of a single bright ring structure, has been widely studied owing to its radius independent of orbital angular momentum (OAM). However, most of the existing works about POVs are limited to single ring structure. Flexible shaping of intensity distribution of POVs is vital for multiple applications. In this paper, we propose a method generate phase tunable multi-ring perfect optical vortices (MR-POVs) where each ring size is independent of its OAM. The scheme is based on the radical discontinuous spiral phase plate (RD-SPP) which introduces controllable phase jumps along radial direction. It is experimentally demonstrated that the vortex nature of the MR-POVs through an interferometric method, showing that each ring of MR-POVs possesses same topological charge value (magnitude and sign), and the intensity ratio between each ring can be freely regulated by adjusting phase distribution, which could offer more flexible optical gradient force for guiding and transporting particles. In addition, simulation and experimental results show that the integer and fractional MR-POV can generated by the independent regulation of angular and radial factors. This work expands our understanding of multi-ring POV and may provide a new idea for optical tweezers and OAM communications.

This Conference Presentation, “Vectorial metagrating for multidimensional optical field manipulation,” was recorded for Photonics Asia 2021, held in Nantong, China.

Photonic spin-orbit interaction has attracted much attention in recent years. This talk first reports the efficient generation of ultra-compact optical vortex (OV) in achiral nanostructures, which has a radius of only 1 μm and possesses a signal-to-noise ratio larger than 6 dB. A spin-selective and phase-resolved scanning near-field optical microscope (SNOM) is employed to probe and visualize the OV generation process in the spin basis. Furthermore, a SNOM system is developed for probing and analyzing nonlinear optical signals in nanostructures with subwavelength resolution, which images the near-field third-harmonic generation from an anapole dark-mode state in a silicon nanodisk.

This Conference Presentation, “β-Sn-based plasmonic materials and their near-field enhancement performance” was recorded for Photonics Asia 2021, held in Nantong, China.

Currently, different shapes and sizes of silver and gold nanoparticles are being studied in many fields of plasmonic energy harvesting device including plasmonic solar cells due to their unique plasmonic properties, particularly in the visible and NIR-region (400-1200 nm). In this experiment, Finite Element Method is used to study the absorption, scattering and extinction spectra of the metal nanoparticles for better understanding of plasmonic effects with the application of COMSOL Multiphysics. Furthermore, the influences of the nanoparticle size, geometry and surrounding dielectric medium on the plasmon resonance peak of the metal nanoparticle is studied using the same software and the results are being analysed in this paper. It is observed that optical absorption and the plasmon peaks can be adjusted by altering sizes and shape of nanoparticles in order to obtain the desired level of absorption. Other parameter such as correlation of multipole resonance with the dipole resonance is also being presented. Key interesting phenomenon which is detected during this experiment is that Ag nanoparticle as its size increases beyond 50 nm, exhibits a multipole resonance peak in the near UV region in addition to the dipole resonance peak, whereas the same is not observed in the case of Au nanoparticle. The origin of this multipole resonant peak shall be further discussed along with its applicability to design efficient plasmonic devices.

The non-ionizing radiation and the high sensitivity to weak interactions of terahertz (THz) waves make THz technology a great applicability in the field of biosensing and medical detection. Besides, benefitted from the flexible capability of metasurface in manipulating the electromagnetic (EM) waves, the high-sensitivity THz sensors can be achieved to promote the development of THz sensing. However, the polarization dependence of hybrid-resonances-based metasurface and the single resonance cause the reduction in sensitivity, which is urgent to be settled. In this paper, we proposed a centrosymmetric metasurface to produce high-quality and polarization-insensitive resonance for improving the sensitivity of THz sensing. The designed metasurface is locally asymmetric, which can induce the high-quality Fano resonance. However, the entire structure is centrosymmetric and thus exhibits polarization-independent characterization. The designed metasurface possesses a polarization-independent resonance peak of transmittance spectrum in 0.1-2THz, which also shows high sensitivity related to ambient refractive index. The advantage of transmitted structure and polarizationindependent resonance can relief the difficulty of measurement. We believe these studies will promote the development of high-sensitivity THz biosensing.

Coupled plasmonic systems are of great interest and have many applications such as information processing and sensing. By choosing proper geometric configurations of coupled plasmonic systems, one can obtain various optical properties. However, some interesting and important effects could not be described by earlier methods. We develop an improved method for coupled plasmonic nanoparticle systems that maps geometric configurations to optical properties more accurately. With the improved method, we realize a low-loss cavity of metallic nanoparticles through a proper geometric configuration, and we find a limit to the loss in the metallic nano-cavity. We also use this method to realize an exceptional point and exceptional nexus in a hybrid plasmonic system. Finally, we predict asymmetric coupling, which leads to chirality and directional energy transfer.

We investigated in situ the interaction between a single gold nanorod and monolayer transition metal dichalcogenides (TMDCs) by atomic force microscopy nanomanipulation and single-particle spectroscopy.We observed that the resonant scattering peak of the hybrid redshifted, the full width at half maximum of the scattering resonance narrowed and the scattering intensity increased compared with those of the same nanorod before coupling with monolayer TMDCs. These results were understood with the aid of finite-difference time-domain simulations, the Fano model, and the classical oscillator model. Also, the spectral features varied with the distance between the nanorod and TMDCs, and the interaction was mainly attributed to the resonant energy transfer effect. Our findings clarify the influence of TMDCs on the plasmonic resonance and contribute to a deeper understanding of the plasmon exciton interaction.

Laser induced breakdown spectroscopy (LIBS) is an analysis technique based on laser plasma atomic emission spectroscopy. Because of its speed, non-destructive and high sensitivity, it is widely used in various fields. In order to study the laser-induced breakdown spectra of heavy metals and non-metal elements in the soil, and solve the problem of low accuracy of LIBS quantitative analysis due to spectral baseline drift, an Adaptive Iterative Re-weighted Partial Least Squares (air-PLS) baseline correction method is proposed to improve the accuracy of LIBS quantitative analysis. In this paper, 8 kinds of standard soil samples are used, 2 grams of each were extracted and placed in a tableting mold, using a 20MPa hydraulic press to form a smooth sheet with a diameter of 30mm and a thickness of 3mm for use. The laser energy was set to 30mJ, and the pulse repetition frequency was set to 5Hz. Plasma spectral lines of metal element Mg of different samples were obtained through experiments, and linear PLS was used to model and analyze the original spectrum and the spectrum after baseline correction respectively. Experimental results show that the accuracy of LIBS quantitative analysis is greatly improved after baseline correction. After using the method described in this article for baseline correction, the coefficient of determination R² increased from 0.9553 to 0.9858, and the root mean square error RMSEC decreased from 1.5610 to 0.8571. The accuracy of LIBS quantitative analysis has been significantly improved. The study of this technology can provide guidance for the quantitative analysis of Mg and other elements in the soil.

The strong interaction between several components forms the hybridized plexciton state and yields multiple Rabi splittings. We propose an integrated structure, J-aggregates molecular dye and monolayer WS₂ wrap around the core-shell Au@Ag nanorods layer by layer, and realize an active-controlled strong exciton-plasmon-exciton coupling, resulting in three plexciton branches. We build a coupled oscillator model theory to describe the interaction, finely reproduce the derived scattering spectra by the finite-difference time-domain (FDTD) method. The amount of J-aggregates and the layer of WS₂ can actively modulate the coupling strength between excitons and the localized surface plasmon resonances. The core-multishell structure is experiment-feasible for the unusual WS₂ nutshell riches in defects state and protects J-aggregates from dye leakage and photobleaching. The multiple Rabi splittings and its dynamic control may have potential application in sensing and catalysis at the nanoscale.

Accurately capturing the spatiotemporal information of surface plasmon polaritons (SPPs) is the basis for expanding SPPs applications. We record time-resolved nonlinear photoemission electron microscopy (TR-PEEM) images of weakly excited femtosecond SPPs launched from a rectangular trench milled into a flat silver film. Experimental results show that the overall photoelectron yield is greatly enhanced (typically 6-fold enhancement with the comparison of that without 400nm pulse) in this configuration. The spatiotemporal evolution of SPP can be easily investigated with its carrier wavelength, group velocityand phase velocity. The improvement of photoemission yield is interpreted by the quantum pathway for two-color with changing the nonlinear for photoemission. It is found that the contrast between bright and dark fringes of SPPs is significantly improved compared to the single-color scheme due to the improvement of quantum pathway channels for photoemission. These findings complete the underlying physics of two-color PEEM optimized SPP spatiotemporal imaging.

Realizing multiple beam shaping functions in a single plasmonic device is the key to realizing photonic integration. Surface Plasmon Polariton (SPP) Bessel-like Beams and Bottle Beams have potential applications in nanophotonics, especially in near-field optical trapping, micro-manipulation, and on-chip interconnect circuits. Thus, it is very interesting to find new approaches for simultaneous generation of surface plasmon polariton Bessel-like beams and bottle beams in a single photonic device. The wavelength-manipulated Bessel SPP beam and Bottle beam emitters devices are composed of four and five compact coupling elements with a specific spatial distribution, respectively. Besides, as the wavelength of the incident light is changed, the generated Bessel-like SPP beam and SPP Bottle beam can be directionally excited on one side of the transmitter and the launching direction can be dynamically selected. The design scheme of the proposed device provides a new means for constructing plasmonic devices with multiple beam shaping functionalities.

The remote excitation based on the propagating surface plasmons (PSP) is becoming increasingly extensive. Here, we study the dynamics of the localized surface plasmons (LSP) remotely excited by PSP on the gold film using the finitedifference time-domain numerical simulations method. The results show that the spectra of LSP excited by PSP change along with its excitation location, showing a unique phenomenon that the spectra exhibit a redshift tendency compared to the LSP excited by the traditional laser source. By comparing with the dynamics of LSP excited by a laser source, the unique near-field characteristics of that excited by PSP can be obtained. Furthermore, we find that the dephasing time of LSP excited by the PSP is longer than by the traditional laser source. We believe the results of this study can be used to improve the efficiency of remote catalytic reactions and provide new ways to prolong the dephasing time.

Strong and controllable circular dichroism (CD) is of great significance in enormous applications of life science. Here we have theoretically investigated the CD response in an Au split-ring resonator (SRR)/graphene nano-ribbon arrays on a metal substrate. The circular dichroism (CD) intensity in the proposed structure can approach 50%. Our theoretical investigation indicate that the strong CD is arisen from the symmetry breaking with the longitudinal plasmonic coupling in this hybrid system. More interestingly, we find that the strong optical CD can be very robust to the change of geometrical parameters of SRR and graphene nanoribbon as well as their vertical separation. Our design provides a new route for developing the compact and robust optical chiral devices in application of biochemical sensing and optical communication.

Live cell microscopy technology, especially cell three-dimensional refractive-index reconstruction, is one of the important single-cell analysis methods, which can investigate subcellular organelles and biological mechanisms. Compared with the method of rotating the illumination light, rotating cells can obtain the complete internal structure information of the cell. However, cell rotation based reconstruction methods typically rotate cells in low operation throughput and image unstably in a low sensitivity. To bridge this gap, we demonstrate a combination strategy that uses acoustically oscillating bubble array based acoustofluidic device to simultaneously rotate cells in large-scale, and sets up a wDPM module to record cell quantitative phase maps with a high temporal and spatial phase sensitivity due to the common-path geometry and white light illumination. Result shows the phase accuracy of this system is less than 6.7%, the phase spatial consistency does not exceed 4%.

Nanoscale single photon source is an important part of on-chip quantum information processing. Gap plasmon structures as a candidate of typical nanostructure, can provide large Purcell enhancement by nanoparticles owing to possessing ultrasmall optical mode volume, and effectively collecting scattering light by nanowire/nanofilm. However, their collecting efficiency is not very high. By introducing quantum Hall effect into optics, topological photonics becomes an important branch in nanophotonics. The edge states are characterized as nonscattering propagation of photons and immunity to a wide class of impurities and defects, i.e., topological protection. However, using topological protection into the Purcell enhancement has not been reported yet. We propose a specific topological photonic structure, i.e., a 1D topological PC containing a resonant nanoantenna. Under the condition of topological protection, we first reveal the edge state-led coupling mechanism; namely, surface plasmons of the antenna almost do not have any influence on the edge state, while the edge state greatly changes the pattern of the local field around the antenna. Based on this mechanism, an obvious absorption reduction in the spontaneous emission spectra is obtained due to the near-field deformation around the antenna induced by the edge state. By embedding an antenna into the topological PC, a strong local field near the antenna leads to a large Purcell enhancement, while the edge state can make almost all scattering photons propagate along some specific directions. As a result, total Purcell factors can reach more than 2×10^4 γ0 (γ0 is the spontaneous emission rate in vacuum), among which the propagating part along the edge state channel is more than 10^4 γ0. By reducing the photonic loss and guiding scattering photons into the edge state, this kind of Purcell enhancement will provide new sight for on-chip quantum light sources such as a single-photon source and nanolaser.

Near field optics is a new interdisciplinary subject that studies optical phenomena very close to objects. The system level theory and method of constructing system sensor, the principle of related algorithm, modeling method and error analysis are analyzed, and the system configurations based on free form is proposed. In order to improve the resolution of the imaging system and reach the theoretical limit, the multiple system optimization method is promoted from the perspective of theory to engineering.

System parameters are important factors that affect the spatial characteristics of laser induced plasma spectral intensity. In this paper, a two-dimensional LIBS model is used to study the effects of laser incident angle and laser energy on the spatial characteristics of spectral intensity. The model is mainly based on fluid dynamics and SAHA equation. In the research, the best laser incidence angle, the best spectrum detection angle of the system under different parameters are obtained. The variation trend of the spectral intensity of laser plasma with the detection angle under different parameters is studied. The results show that 0° is the best incident angle for 1064 nm laser with different delay time and different delay conditions. When the incident angle is 0°, the excited plasma radiation has a stronger spectral signal at different detection angles. Corresponding to the incident angle of 0°, the optimal detection angles are ±41°, ±11° and ±12° at 100 ns, 500 ns and 1000 ns delay conditions, respectively. The simulation results also show that the signal intensity of the plasma radiation spectrum increases and then decreases at the optimal detection angle with the decrease of the absolute value of the detection angle. The experiments have verified the simulation results.

Terahertz (THz) absorbers have attracted considerable attention due to their potential applications. However, the limited bandwidth of THz absorbers limits their further applications. In order to achieve ultra-broadband and high absorption characteristics in the THz band, a double truncated pyramid unit structure combining the hybrid planar structure and the few-layers vertical structure is proposed. The double truncated pyramid unit structure composed of five metal layers and five graphene layers has the advantages of ultra-broadband, tunability, polarization-insensitive, wide-angle absorption. The simulation results show that the absorption coefficient of the absorber is greater than 0.9 from 1.49 THz to 12.72 THz, and the absorption bandwidth is 11.23 THz. The ultra-broadband absorption can be attributed to the size effect. The absorption mechanism can be further explained by surface current distribution and impedance matching theory.

In this paper, we present a study on thermo-optical effect in core-shell silver/thiol-termination ligand nanoparticles. Nanoparticles were dissolved in Dichloromethane. Experimental measurements were carried out using a Z-scan setup. As laser sources we used two 1064 nm lasers: i) 28 ps pulse width laser with 1000 Hz pulse repetition rate; ii) 8 ns pulse width laser with changeable pulse repetition rate 200 – 40 000 Hz. To study what processes lead to refractive index changes we used the polarization-resolved Z-scan method. Comparing ps and ns results showed that response time of single pulse thermal effects for organic solvents depends on beam size while for nanoparticles it corresponds to nanoparticle size. Measurements with ns laser using different lenses and pulse repetition rate showed that thermal response scales with the ratio of laser pulse repetition rate times beam size squared.

In this paper, the plasmon resonance splitting on the anodized modified titanium has been studied. The plasmons absorption process in the permittivity functions spectra and reflectance spectra of p- and s-polarized light on the titanium oxide surface have been analyzed when the surface roughness parameters are changing. The surface roughness values were also estimated in this paper. Spectral features of the negative refractive index in the area of surface plasmon generation on the rough titanium-oxide film interface have been also presented in this paper. Surface roughness parameters are also determined. The upconversion luminescence enhancement of the ytterbium oxide on the rough titanium surface was observed in this work.

This article is a continuation of research in the field of modeling nanoparticles by various FDTD methods. This article clarifies what geometrical parameters are necessary to obtain the highest value of the elec tric field for core-shell particles with a gold (Au) core with a silicon (SiO₂) shell; the other part is related to the modeling of silver nanorods (Ag). Both simulations were performed under the action of one plane polarized wave 𝜆 = 532 nm. Parameters such as the height of the rod, the radius of the cross section of the rod were varied; for the core-shell particle, the radius of the particle and the thickness of the SiO₂ layer were varied. The analysis of the values of the electric (E) field component of these particles is carried out and compared with each other. The advantage of theoretical modeling by the FDTD method using our algorithm is shown. The presented data can be used as a basis for controlled chemical synthesis of spherical nanoparticles.

This work presents the process of creating laser-induced surface structures by fs laser radiation with circular polarization and the study of their optical properties by ellipsometry method. This report presents SEM images of the Cu and Cu/Au surfaces and the studies of spectral features of dielectric permittivity function and reflection coefficients of s- and p-polarized light.