Surface Wave Resonance Research Articles

Numerical temporal-spectral analysis of non-scattering THz nanoscopy with resonant cantilevered tips.

Scattering-type scanning near-field optical microscopy (s-SNOM) under the excitation of single cycle picosecond (ps) pulse provides access to terahertz (THz) time-resolved nanoscopy. However, the development of THz nanoscopy has been greatly limited due to the inherently low efficiency of the scattered field and the convolution of the intrinsic material response with the extrinsic response of the cantilevered tip. In this work, we quantitatively study the near-field time-delayed pulse transients of resonant cantilevered tips, observing localized tip-enhanced coupling as well as delocalized collective charge oscillations propagating as resonant surface waves along cantilevered tips. By numerical temporal-spectral analysis, the phonon resonance of the topological insulator Bi2Se3 can be effectively extracted from the resonant surface waves at the end of the cantilever. We demonstrate that after propagating 600 µm, the intensity of near-field signals extracted from the resonant surface waves is about three orders higher than that from the traditional scattering field. Our research reveals the delocalized tip-enhanced light-matter interaction in propagating surface waves and proposes a promising route to non-scattering THz nanoscopy.

Resonant surface waves in an oscillating periodic tank with a submerged hill

Experimental studies on the sloshing of fluid layers are usually performed in rectangular tanks with fixed boundaries. In contrast, the present study uses a 4.76-m-long circular channel, a geometry with open periodic boundaries. Surface waves are excited by means of a submerged hill that, together with the tank, performs a harmonic oscillation. Laboratory measurements are made using 18 ultrasonic probes, evenly distributed over the channel to track the wave propagation. It is shown that a two-dimensional long-wave numerical model derived via the Kármán–Pohlhausen approach reproduces the experimental data as long as the forcing is monochromatic. The sloshing experiments imply a highly complex surface wave field. Different wave types such as solitary waves, undular bores and antisolitary waves are observed. For order one $\delta _{hill} = h_{hill}/h_0$ , where $h_0$ is the mean water level and $h_{hill}$ the obstacle's height, the resonant reflections of solitary waves by the submerged obstacle give rise to an amplitude spectrum for which the main resonance peaks can be explained by linear theory. For smaller $\delta _{hill}$ , wave transmissions lead to major differences with respect to the more common cases of sloshing with closed ducts having fully reflective ends for which wave transmission through the end walls is not possible. This ultimately results in more complex resonance diagrams and a pattern formation that changes rather abruptly with the frequency. The experiments are of interest not only for engineering applications but also for tidal flows over bottom topography.

Time-Domain-Filtered Terahertz Nanoscopy of Intrinsic Light-Matter Interactions.

Terahertz (THz) technology holds great potential across diverse applications, including biosensing and information communications, but conventional far-field techniques are limited by diffraction. Near-field optical microscopy overcomes this barrier through a sharp tip that concentrates incident THz waves into nanometric volumes, detecting scattered near-field to reveal nanoscale optical properties. However, owing to the large THz wavelengths, resonant surface waves arising on the tip and cantilever obscure the intrinsic response. Here we combine near-field microscopy with THz time-domain spectroscopy and implement time-domain filtering with an elongated cantilever to eliminate this artifact, achieving intrinsic nanospectroscopy and nanoimaging. By applying this technique, we distinguish and characterize historical pigments of an ancient sculpture, such as vermilion and red lead, on the nanoscale. We also unravel deep-subwavelength localized resonance modes in THz optical antennas, demonstrating capabilities for THz nanophotonics. Our work advances THz nanoimaging and nanospectroscopy techniques to probe intrinsic nanoscale THz light-matter interactions.

Nano-Photonic Crystal D-Shaped Fiber Devices for Label-Free Biosensing at the Attomolar Limit of Detection.

Maintaining both high sensitivity and large figure of merit (FoM) is crucial in regard to the performance of optical devices, particularly when they are intended for use as biosensors with extremely low limit of detection (LoD). Here, a stack of nano-assembled layers in the form of 1D photonic crystal, deposited on D-shaped single-mode fibers, is created to meet these criteria, resulting in the generation of Bloch surface wave resonances. The increase in the contrast between high and low refractive index (RI) nano-layers, along with the reduction of losses, enables not only to achieve high sensitivity, but also a narrowed resonance bandwidth, leading to a significant enhancement in the FoM. Preliminary testing for bulk RI sensitivity is carried out, and the effect of an additional nano-layer that mimics a biological layer where binding interactions occur is also considered. Finally, the biosensing capability is assessed by detecting immunoglobulin G in serum at very low concentrations, and a record LoD of 70 aM is achieved. An optical fiber biosensor that is capable of attaining extraordinarily low LoD in the attomolar range is not only a remarkable technical outcome, but can also be envisaged as a powerful tool for early diagnosis of diseases.

Bloch-surface-wave resonance in a cavity resonator for focusing retroreflection.

A wavelength-selective retroreflector for a diverging wave will be an attractive external mirror for compact wavelength-stabilized semiconductor lasers and consists of a focusing grating coupler and a cavity resonator. In this Letter, the retroreflector utilizing a Bloch surface wave (BSW) resonance was theoretically investigated for improving the retro-reflectance in comparison to a previously reported structure utilizing guided-mode resonance (GMR). A retroreflector with an aperture size of 31 µm and focal length of 67 µm was designed for an operation wavelength of 1550 nm. The maximum retro-reflectance is predicted by numerical simulation to be higher by 11% than that of the GMR-based retroreflector.

Temporal and spectral signatures of the interaction between ultrashort laser pulses and Bloch surface waves

The resonant excitation of Bloch Surface Waves (BSWs) in dielectric one-dimensional photonic crystals is becoming a realistic photonic solution for surface integration in many domains, from spectroscopy to local field management. Bringing BSWs to ultrafast and nonlinear regimes requires a deep knowledge of the effects that the photonic crystal dispersion and the resonant surface wave excitation have on the ultrashort laser pulses. We report on the experimental evidence of spectral and temporal modifications of the radiation leaving a planar one-dimensional photonic crystal after coupling to BSWs. In such a resonant condition, a characteristic long temporal tail is observed in the outgoing pulses. Observations are performed by employing both frequency-resolved optical gating and field cross-correlation techniques.

Comparative Analysis of Ethanol Gas Sensors Based on Bloch Surface Wave and Surface Plasmon Resonance

Ethanol plays a crucial role in modern industrial processes and consumer products. Despite its presence in human activity, short and long-term exposure to gaseous ethanol poses risks to health conditions and material damage, making the control of its concentration in the atmosphere of high importance. Ethanol optical sensors based on electromagnetic surface waves (ESWs) are presented, with sensitivity to ethanol vapours being achieved by the inclusion of ethanol-adsorptive zinc oxide (ZnO) layers. The changes in optical properties modulate the resonant conditions of ESWs, enabling the tracking of ethanol concentration in the atmosphere. A comprehensive comparative study of sensor performance is carried out between surface plasmon resonance (SPR) and Bloch surface wave (BSW) based sensors. Sensor efficiency is simulated by transfer matrix method towards optimized figures of merit (FoM). Preliminary results validate ethanol sensitivity of BSW based sensor, showcasing a possible alternative to electromagnetic and plasmonic sensors.

Coherent spin exchange scattering of low-energy electrons by Ni2+ ions in antiferromagnetic crystal NiO under surface wave resonance: experimental and theoretical results revisited

Coherent spin exchange scattering of low-energy electrons by Ni2+ ions in antiferromagnetic crystal NiO under surface wave resonance: experimental and theoretical results revisited

Forward Brillouin Scattering Spectroscopy in Optical Fibers with Whispering‐Gallery Modes

AbstractOpto‐mechanical interactions in different photonic platforms as optical fibers and optical microresonators are raising great attention, and new exciting achievements have been reported in the last few years. Transverse acoustic mode resonances (TAMRs) in optical fibers –which can be excited optically via electrostriction and generate forward Brillouin scattering (FBS)– are being promoted as the physical mechanism for new fiber‐sensing concepts. Here, the study reports a novel approach to detect and characterize opto‐excited TAMRs of an optical fiber based on the interplay with optical surface wave resonances, i.e., optical whispering‐gallery mode (WGM) resonances. TAMRs induce perturbations in the geometry and the dielectric permittivity of the fiber over the entire cross‐section. It is shown that these perturbations couple the acoustic with the optical resonances and affect WGMs in a noticeable way. The study proposes and demonstrates the use of WGMs for probing opto‐excited TAMRs in optical fibers. This probing technique provides the narrowest linewidths ever reported for the TAMRs and demonstrates an optimum efficiency for the detection of low‐order TAMRs. The interplay between sensitivity, bandwidth, and Q factor of the WGM resonance is discussed.

Side-polished photonic crystal fiber sensor with ultra-high figure of merit based on Bloch-like surface wave resonance

A Bloch surface wave (BSW) resonance configuration is introduced for biosensing with an ultra-high figure of merit (FOM). The BSW excitation is realized through the evanescent field of the core-guided fundamental mode of a side-polished photonic crystal fiber (PCF). By taking advantage of the air hole periodic microstructure of the PCF cladding, the BSW platform can be achieved with only a single high refractive index dielectric layer on its flat surface. The dielectric layer deposited on the polished surface of the PCF modifies the local effective refractive index, allowing direct manipulation of the BSWs, whereby the resonance wavelength of the surface wave can be adjusted by choosing the material and thickness of this layer. Here, we numerically investigate Bloch-like surface wave (BLSW) resonance conditions around telecom wavelengths for silicon, titanium dioxide, copper monoxide, and aluminum oxide termination layers. The BLSW excitation platform materials have low loss, which results in higher surface field enhancements and narrower resonances, which are advantageous properties for the sensors. The obtained results open new avenues for the application of optical surface waves in biosensing with high FOM. Furthermore, these results show a much higher figure of merit (FOM) than traditional approaches, allowing for increased sensitivity and accuracy.

Crossover of surface waves and capillary-viscous-elastic transition in soft biomaterials detected by resonant acoustic rheometry

Viscoelastic properties of hydrogels are important for their application in science and industry. However, rheological assessment of soft hydrogel biomaterials is challenging due to their complex, rapid, and often time-dependent behaviors. Resonant acoustic rheometry (RAR) is a newly developed technique capable of inducing and measuring resonant surface waves in samples in a non-contact fashion. By applying RAR at high temporal resolution during thrombin-induced fibrin gelation and ultraviolet-initiated polyethylene glycol (PEG) polymerization, we observed distinct changes in both frequency and amplitude of the resonant surface waves as the materials changed over time. RAR detected a series of capillary-elastic, capillary-viscous, and visco-elastic transitions that are uniquely manifested as crossover of different types of surface waves in the temporally evolving materials. These results reveal the dynamic interplay of surface tension, viscosity, and elasticity that is controlled by the kinetics of polymerization and crosslinking during hydrogel formation. RAR overcomes many limitations of conventional rheological approaches by offering a new way to comprehensively and longitudinally characterize soft materials during dynamic processes.

Development of the Tele-Measurement of Plasma Uniformity via Surface Wave Information (TUSI) Probe for Non-Invasive In-Situ Monitoring of Electron Density Uniformity in Plasma Display Fabrication Process.

The importance of monitoring the electron density uniformity of plasma has attracted significant attention in material processing, with the goal of improving production yield. This paper presents a non-invasive microwave probe for in-situ monitoring electron density uniformity, called the Tele-measurement of plasma Uniformity via Surface wave Information (TUSI) probe. The TUSI probe consists of eight non-invasive antennae and each antenna estimates electron density above the antenna by measuring the surface wave resonance frequency in a reflection microwave frequency spectrum (S11). The estimated densities provide electron density uniformity. For demonstration, we compared it with the precise microwave probe and results revealed that the TUSI probe can monitor plasma uniformity. Furthermore, we demonstrated the operation of the TUSI probe beneath a quartz or wafer. In conclusion, the demonstration results indicated that the TUSI probe can be used as an instrument for a non-invasive in-situ method for measuring electron density uniformity.

Wave propagation in a circular channel: sloshing and resonance

Surface wave resonance of a liquid (water) layer confined in a circular channel is studied both experimentally and numerically. For the experiment, eight unevenly distributed ultrasonic distance sensors measure the local height of the wave surface. The resonance curves show maxima only for odd multiples of the fundamental resonance frequency f_0. We explained this behavior using a simple intuitive “ping-pong” like model. Collision of wave fronts can be observed for higher frequencies. Also, the wave reflection on the walls can be treated as wave collision with itself. The non-linearity seems to be weak in our study so the delay in the wave propagation before and after the collision is small. Time-space plots show localized propagating waves with high amplitudes for frequencies near resonance. Between the peaks low amplitude and harmonic patterns are observed. However, for higher frequencies, the frequency band for localized waves becomes wider. In the Fourier space-time plane, this can be observed as a point for the harmonic patterns or a superposition of two lines: one line parallel to wave-vector k axis corresponding to the excitation frequency f_0 and a second line with inclination given by wave propagation velocity sqrt{gh}. For planned future work, this result will help us to reconstruct the whole water surface elevation using time-series from only a few measurement points

Spectral tuning of Bloch Surface Wave resonances by light-controlled optical anisotropy.

Fostered by the recent advancements in photonic technologies, the need for all-optical dynamic control on complex photonic elements is emerging as more and more relevant, especially in integrated photonics and metasurface-based flat-optics. In this framework, optically-induced anisotropy has been proposed as powerful mean enabling tuning functionalities in several planar architectures. Here, we design and fabricate an anisotropic two-dimensional bull's eye cavity inscribed within an optically-active polymeric film spun on a one-dimensional photonic crystal sustaining Bloch surface waves (BSW). Thanks to the cavity morphology, two surface resonant modes with substantially orthogonal polarizations can be coupled within the cavity from free-space illumination. We demonstrate that a dynamic control on the resonant mode energies can be easily operated by modulating the orientation of the optically-induced birefringence on the surface, via a polarized external laser beam. Overall, reversible blue- and red-shifts of the resonant BSWs are observed within a spectral range of about 2nm, with a moderate laser power illumination. The polymeric structure is constituted by a novel blend of an azopolymer and a thermally-sensitive resist, which allows a precise patterning via thermal scanning probe lithography, while providing a significant structural integrity against photo-fluidization or mass-flow effects commonly occurring in irradiated azopolymers. The proposed approach based on tailored birefringence opens up new pathways to finely control the optical coupling of localized surface modes to/from free-space radiation, particularly in hybrid organic-inorganic devices.

Design of an Artificial Opal/Photonic Crystal Interface for Alcohol Intoxication Assessment: Capillary Condensation in Pores and Photonic Materials Work Together

Alcohol intoxication has a dangerous effect on human health and is often associated with a risk of catastrophic injuries and alcohol-related crimes. A demand to address this problem adheres to the design of new sensor systems for the real-time monitoring of exhaled breath. We introduce a new sensor system based on a porous hydrophilic layer of submicron silica particles (SiO2 SMPs) placed on a one-dimensional photonic crystal made of Ta2O5/SiO2 dielectric layers whose operation relies on detecting changes in the position of surface wave resonance during capillary condensation in pores. To make the active layer of SiO2 SMPs, we examine the influence of electrostatic interactions of media, particles, and the surface of the crystal influenced by buoyancy, gravity force, and Stokes drag force in the frame of the dip-coating preparation method. We evaluate the sensing performance toward biomarkers such as acetone, ammonia, ethanol, and isopropanol and test sensor system capabilities for alcohol intoxication assessment. We have found this sensor to respond to all tested analytes in a broad range of concentrations. By processing the sensor signals by principal component analysis, we selectively determined the analytes. We demonstrated the excellent performance of our device for alcohol intoxication assessment in real-time.

Spectral analysis of localized surface phonon polaritons in resonant silicon carbide hollow cylinder array

Manipulation of the amplitude and frequency of resonant optical surface waves in mid-infrared is of great interest for improvement of photonic devices and vibrational molecule sensing applications. Antennas supporting localized surface phonon polaritons (LSPhPs) fold the optical phonons into periodic pillar array to control the scattering process. Energy exchange, mode evolution and near-field coupling mechanism are investigated thoroughly, and it is demonstrated that the transverse dipole mode in the 6H-silicon carbide hollow cylinder array shows excellent absorption efficiency and tunable capability across a wide spectral range. Dependence of local field on structural parameters in the polarized sub-mode is explored to elucidate the optical properties. Near-field coupling is further evaluated by combining the values of current distribution with multipole decomposition. This study also provides a practical guide to establish a general framework for exploring the spectral tuning and coupling mechanisms of LSPhP modes.

Development of the Measurement of Lateral Electron Density (MOLE) Probe Applicable to Low-Pressure Plasma Diagnostics.

As the importance of measuring electron density has become more significant in the material fabrication industry, various related plasma monitoring tools have been introduced. In this paper, the development of a microwave probe, called the measurement of lateral electron density (MOLE) probe, is reported. The basic properties of the MOLE probe are analyzed via three-dimensional electromagnetic wave simulation, with simulation results showing that the probe estimates electron density by measuring the surface wave resonance frequency from the reflection microwave frequency spectrum (S). Furthermore, an experimental demonstration on a chamber wall measuring lateral electron density is conducted by comparing the developed probe with the cutoff probe, a precise electron density measurement tool. Based on both simulation and experiment results, the MOLE probe is shown to be a useful instrument to monitor lateral electron density.

Резонаторная ячейка с открытым входом на основе диэлектрической пластины на металлической подложке

Possibility of converting the energy of an incident electromagnetic wave to the energy of a surface wave in a dielectric plate on a metal substrate has been confirmed through numerical simulation. To transfer energy between waves of different structures, a diffraction grating placed on the surface of the plate is used. Energy is retained in the plate through the formation of a surface wave resonator by introducing aflush metal walls along the plate’s ends. Thus, the resonant cell with open entrance has been suggested – the energy enters the cell through the whole lit surface of the plate. It is assumed that the dielectric has small losses, and the diffraction grating on its surface consists of the identical bars, which are made of the same dielectric and have small cross section. The resonance in the form of sharp increase of the standing wave amplitude inside the plate, compared to the incident wave amplitude, and correspondingly increase of the incident wave’s energy absorption by the plate takes place at some grating periods. The external manifestation of resonance is a decrease of specular scattering from the plate: the observed decrease of plate’s RCS in the ray reflection direction was from several times to more than three orders of magnitude under different conditions. Stability of numerical solution of the problem of diffraction on the suggested cell follows from the observed smooth variation of the condition number in the vicinity of even the deepest plate’s resonant RCS reduction. Efficiency of surface wave generation by diffraction gratings of different types or by arranging other periodical inhomogeneities on the surface or within the volume of dielectric can be compared according to the depth of resonance.

Effect of interfacial damping on high-frequency surface wave resonance on a nanostrip-bonded substrate

Since surface acoustic waves (SAWs) are often generated on substrates to which nanostrips are periodically attached, it is very important to consider the effect of an interface between the deposited strip and the substrate surface, which is an unavoidable issue in manufacturing. In this article, we propose a theoretical model that takes into account interface damping and calculate the dispersion relationships both for frequency and for attenuation of SAW resonance. These results show that the interface damping has an insignificant effect on resonance frequency; but, interestingly, attenuation of the SAW can decrease significantly in the high-frequency region as the interface damping increases. Using picosecond ultrasound spectroscopy, we confirm the validity of our theory; the experimental results show similar trends both for resonant frequency and attenuation in the SAW resonance. Furthermore, the resonant behavior of the SAW is simulated using the finite element method, and the intrinsic cause of interface damping on the vibrating system is discussed. These findings strongly indicate the necessity of considering interfacial damping in the design of SAW devices.

Low-Profile Broadband Dual-Polarization Double-Layer Metasurface Antenna for 2G/3G/LTE Cellular Base Stations

A double-layer metasurface is proposed to realize the low profile of a broadband dual-polarized antenna for cellular base-station applications. The proposed metasurface is formed by the two layers of printed metallic patch unit cells on either substrate surface to miniaturize the metasurface size and enhance design flexibility by regulating the extent of electromagnetic coupling between the two layers. Despite the low profile of the antenna, a wideband operation is accomplished by operating the metasurface in the nonresonant region that facilitates wideband phase compensation and its truncation to a finite dimension with an additional transverse electric (TE) surface wave resonance. The guidelines for the design of the surface is derived from a comparison of unit cell structures and an approach is introduced to correlate their potential with surface susceptibility parameters. A detailed parametric study addresses the critical concern on the overall dimensions of the finite metasurface. A ±45°-polarized dipole antenna with an overall thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.15~\lambda _{0}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength in free space at the center operating frequency) is designed as example. The measured results show a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert \le -10$ </tex-math></inline-formula> dB impedance bandwidth of 46.4% over the frequency range of 1.69–2.71 GHz with average boresight gain of 9 dBi with a ground plane of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.1\lambda _{0} \times 1.1\lambda _{0}$ </tex-math></inline-formula> , well covering 2G (1.71–1.92 GHz), 3G (1.88–2.17 GHz), and LTE (2.3–2.4 GHz and 2.5–2.69 GHz) bands.