Resonance Wavelength Research Articles

Sound absorbers from walnut shell waste: measurement and models

Waste walnut shells have been cleaned, dried, chopped, glued, pressed, and molded to form porous cylinders for measurement of normal incidence sound absorption coefficient spectra in an impedance tube. Porosities and flow resistivities have been measured non-acoustically. Field Emission Scanning Electron Microscopy images, used to obtain fragment size for determining shell density, reveal that the fragment surfaces are rough, which may influence acoustical performance. Measured absorption spectra have been compared with predictions of two analytical models for acoustical properties of rigid porous media, which assume microstructures of identical uniform parallel slanted slits (SS) and non-uniform cylindrical pores with a log normal radius distribution (NUPSD) respectively. Measured values of flow resistivity and porosity are used in the models but tortuosity is adjusted to give best agreement with the quarter wavelength resonance in the measured absorption coefficient spectra. Predictions agree best with data for samples made from the smallest shell fragments. These samples have the highest values of tortuosity, flow resistivity and offer good absorption at speech frequencies which suggests that recyclable and sustainable sound absorbers made from walnut shell wastes could be useful for controlling indoor reverberation..

The potential of heavily doped n-type silicon in plasmonic sensors

In this paper, we introduce a CMOS-compatible H-shaped plasmonic sensor with a silicon-insulator-silicon (SIS) configuration, utilizing highly doped n-type silicon as an alternative to traditional plasmonic materials like silver and gold. By employing precise carrier concentrations, we tune both the real and imaginary parts of permittivity, enabling the negative real permittivity required for efficient surface plasmon polariton (SPP) propagation. Our findings reveal a significant correlation between silicon doping concentration and sensitivity, highlighting the optimization potential of n-type silicon for advanced plasmonic applications. Through Finite Element Method (FEM) optimization, the sensor achieved a peak sensitivity of 5841.43 nm/RIU and a FOM of 23.8426. The sensor’s capabilities extend to temperature sensing with PDMS and ethanol, blood electrolyte detection for sodium and potassium, chemical detection, and magnetic field sensing. By utilizing minute changes in resonant wavelength through SPPs and SIS structures, our approach underscores n-type silicon’s potential in advancing plasmonic sensor technology.

Strongly localized nanolaser based on the vertical dipole governed by bound states in the continuum

Ultrasmall mode volumes and strongly localized fields are crucial for the miniaturization and performance enhancement of nanolasers. Here, we demonstrate a nanolaser based on a vertical dipole resonance coupled to its mirror in a periodic array of nanopillars on an Ag mirror, governed by symmetry-protected bound states in the continuum (BICs), which possess extremely small mode volumes and high field enhancement. A nanolaser with a strongly localized field size of only ∼λ/300 (where λ is the resonant wavelength) can be explored by using this vertical dipole. Compared to a vertical dipole nanolaser without a silver mirror, the effective mode volume can be reduced by an order of magnitude, and the threshold can decrease from 5.85 to 0.337 μJ/mm2. Additionally, by controlling further investigated the angle of the incident light, we can also adjust the threshold of the nanolaser. When the incidence angle is adjusted from 9° to 1°, the threshold can be reduced from 1.43 to 0.299 μJ/mm2.

Spectral Control by Silver Nanoparticle-Based Metasurfaces for Mitigation of UV Degradation in Perovskite Solar Cells.

Perovskite solar cells are considered to be one of the most promising solar cell designs in terms of photovoltaic efficiency. However, their practical deployment is strongly affected by their short lifetimes, mostly caused by environmental conditions and UV degradation. In this contribution, we present a metasurface made of silver nanoparticles used as a UV filter on a perovskite solar cell. The UV-blocking layer was fabricated and morphologically and compositionally analyzed. Its optical response, in terms of optical transmission, was also experimentally measured. These results were compared with simulations made through the use of a well-proven computational electromagnetism model. After analyzing the discrepancies between the experimental and simulated results and checking those obtained from electron beam microscopy and electron dispersion spectroscopy, we could see that a residue from fabrication, sodium citrate, strongly modified the optical response of the system, generating a redshift of about 50 nm. Then, we proposed and simulated the optical behavior of core-shell nanoparticles made of silver and silica. The calculated spectral absorption at the active perovskite layer shows how the appropriate selection of the geometrical parameters of these core-shell particles is able to tune the absorption at the active layer by removing a significant portion of the UV band and reducing the absorption of the active layer from 90% to 5% at a resonance wavelength of 403 nm.

Dynamically tunable highly sensitive sensor based on graphene and black phosphorus composite metamaterial

Focusing on the realization of multiple-detection-point sensors in the mid-infrared band, a dynamically tunable high-sensitive index refraction sensor based on graphene and black phosphorus (BP) composite metamaterial is proposed. By adjusting the height of the grating, the strength of the structural plasmon-induced absorption (PIA) can be enhanced within a certain range. The energy transfer mechanism of the system is analyzed by the coupled mode theory (CMT), the theoretical data of CMT fit well with the FDTD simulation results, which proves that the analysis of the system using the CMT model is correct. The resonant wavelengths of the PIA can be efficiently modulated by changing the Fermi level of graphene and the carrier density of BP. It is worth mentioning that under different environmental refractive indexes, our proposed system has excellent sensing characteristics in the mid-infrared band. The maximum sensitivity and the maximum figure of merit (FOM) are up to 5.174 μm/RIU and 26.449, respectively. This research could play an important role in mid-infrared optical sensors.

All-Optical Trapping and Programmable Transport of Gold Nanorods with Simultaneous Orientation and Spinning Control.

Gold nanorods (GNRs) are of special interest in nanotechnology and biomedical applications due to their biocompatibility, anisotropic shape, enhanced surface area, and tunable optical properties. The use of GNRs, for example, as sensors and mechanical actuators, relies on the ability to remotely control their orientation as well as their translational and rotational motion, whether individually or in groups. Achieving such particle control by using optical tools is challenging and exceeds the capabilities of conventional laser tweezers. We present a tool that addresses this complex manipulation problem by using a curve-shaped laser trap, enabling the optical capture and programmable transport of single and multiple GNRs along any trajectory. This type of laser trap combines confinement and propulsion optical forces with optical torque to transport the GNRs while simultaneously controlling their rotation (spinning) and orientation. The proposed system facilitates the light-driven control of GNRs and the quantitative characterization of their motion dynamics including transport speed, spinning frequency, orientation, and confinement strength. We experimentally demonstrate that remote control of the GNRs can be achieved both near a substrate surface (2D trapping) and deep within the sample (3D all-optical trapping). The motion dynamics of two sets of off-resonant GNRs, possessing similar aspect ratios but different resonance wavelengths, are analyzed to highlight the role played by their optical and mechanical properties in the optical manipulation process. The experimental results are supported by a theoretical model describing the observed motion dynamics of the GNRs. This optical manipulation tool can significantly facilitate applications of light-driven nanorods.

Thin-film dielectric characterization by bound state in the continuum in high contrast grating

Subwavelength high contrast grating (HCG) is renowned for its remarkable ability to produce sharp optical resonance, known as the bound state in the continuum (BIC). Due to the strong surface field enhancement, the resonant wavelength and quality factor (Q factor) are highly sensitive to the dielectric properties of the surrounding medium. We propose utilizing this extraordinary phenomenon for thin-film dielectric characterization based on a film-substrate-grating configuration. By optimizing the geometrical parameters to control the cross-interference between guided modes in the grating and self-interference of propagating wave in the substrate slab, an accidental BIC with a Q factor reaching 104 is excited. Using this BIC, two retrieval methods based on contour mapping of resonant wavelength and Q factor are proposed to extract the complex permittivity (εf) of the film under test. It has been demonstrated that with a film thickness as thin as 10−5 times the grating period, the error in the retrieved Re[εf] is below 2%, and that of Im[εf] is below 10%. The proposed design is a strong candidate for non-destructive dielectric characterization of thin films with thicknesses below one-thousandth of the operating wavelength. This characterization technique can facilitate the development of high-frequency devices for the 6 G high-speed communication.

Enhanced biosensing with rhombic ring resonator in 2D photonic crystals for proteinuria detection

A two-dimensional (2D) photonic crystal (PC) based biosensor was developed and studied to detect albumin and urea levels in patients with proteinuria. Rhombic ring resonator structures are built with the help of FDTD (Finite Difference Time Domain). After the fields are computed using the 2D-FDTD approach, the normalized transmission spectra are produced by applying the Fast Fourier Transform (FFT) to them. The full width at half maximum (FWHM), Quality factor (Q-factor), Sensitivity, Figure of Merit (FOM), and Limit of Detection (LOD) are 15,466.5, 110 nm/RIU, 0.12 nm, 1100 RIU−1 and 54.34X10−6 RIU respectively, when the resonant wavelength is 1546 nm. The novelty of this the project lies in combining 2D photonic crystal, innovative rhombic ring resonator design and high-performance parameters. The achieved values are notably high, which is a novel achievement in the field of biosensing. The project aims to contribute to the field of biosensors and provide a potential tool for healthcare professionals to monitor diabetes, proteinuria, kidney function and overall health.

Comparative Analysis of Two Different MIM Configurations of a Plasmonic Nanoantenna

AbstractTwo plasmonic nanoantenna configurations—nanodisk and nanostrip arrays—in a metal–insulator-metal (MIM) setup were proposed, optimized, and compared by simulating their optical properties in three-dimensional models using COMSOL Multiphysics software. The optical responses, including electric field enhancement, absorption, reflection, and transmission spectra, were systematically investigated. Optimized geometrical parameters led to a significant enhancement of the electric field within the gap layers and almost perfect light absorptance for both structures. The results showed that the enhancement of the electric field depends on the polarization of the incident light. For both polarizations, the periodic circular nanodisk array showed a stronger field enhancement with an electric field enhancement factor of 6.6 × 106 and TE polarization, and a larger absorptance of 98% at its dipole resonance wavelength, indicating the fundamental plasmonic mode. In addition, weaker resonant modes were observed in the absorptance and reflectance spectra of both nanostructures, with the nanostrips exhibiting sharper and stronger higher-order modes, making them suitable for applications requiring precise wavelength selectivity and narrow-band responses. Despite their different geometric shapes, both structures exhibited similar optimized metal film thickness and nanoparticle height, comparable modes in number and position, and identical optimized light incidence angles. Furthermore, increasing the dielectric gap layer thickness and optimizing it to a specific value revealed its ability to measure the refractive index, making it a promising candidate for sensing applications.

Double-formant PCF-SPR refractive index sensor with ultra-high double-peak-shift sensitivity and a wide detection range

A dual-resonance-peak photonic crystal fiber–surface plasmon resonance (PCF-SPR) refractive index (RI) sensor is designed for different wavelength ranges. The first resonance peak of the sensor is distributed in the wavelength range of 700–2350 nm, while the second peak is distributed in the range of 2350–5550 nm. In addition to detecting analytes using the full spectrum of constraint losses (CLs), it is also possible to use a single resonance peak to achieve the detection of analytes. By systematically optimizing the nanowire diameter, the diameter of the inner and outer layer air hole, the width of the groove, the polishing depth, and the distance from the outer layer air hole to the fiber core, the optimal structure of the sensor is finally determined. In this study, the sensor was studied by numerical analysis, and the characteristics of the sensor were evaluated by wavelength detection technology. The results show that within the RI range of 1.24–1.37, the sensor has a maximum wavelength sensitivity (WS) of 54700 nm/RIU for detecting the RI of analytes. Within the above refractive index range, the regression coefficient R2 of the dual-peak-resonance wavelength is 0.99993, ensuring the accuracy of the estimated resonance wavelength of the sensor. In addition, the sensor can also use dual-peak-shift sensitivity (DPSS) to detect the refractive index, which is a relatively new sensing technology. The maximum DPSS of the sensor is 95300 nm/RIU. Due to its high sensitivity and unique dual-peak characteristics, this sensor has wide application prospects in medical diagnosis, environmental monitoring, food safety, and other fields.

Slowing Down a Coherent Superposition of Circular Rydberg States of Strontium.

Rydberg alkaline earth atoms are promising tools for quantum simulation and metrology. When one of the two valence electrons is promoted to long-lived circular states, the second valence electron can be optically manipulated without significant autoionization. We harness this feature to demonstrate laser slowing of a thermal atomic beam of circular strontium atoms. By driving the main ion core 422nm wavelength resonance, we observe a velocity reduction of 50 m/s without significant autoionization. We also show that a superposition of circular states undergoes very weak decoherence during the cooling process, up to the scattering of more than 1000 photons. This robustness opens new perspectives for quantum simulations over long timescales with circular atoms, while simultaneously cooling their motional state. It makes it possible to mitigate the harmful effects of unavoidable heating due to spin-motion coupling during a quantum simulation.

Development of a localized surface plasmon-enhanced electron beam-pumped nanoscale light source for electron beam excitation-assisted optical microscopy.

We have demonstrated localized surface plasmon (LSP)-enhanced cathodoluminescence (CL) from an atomic layer deposition (ALD)-grown Al2O3/ZnO/Al2O3 heterostructure to develop a bright nanometer-scale light source for an electron beam excitation-assisted (EXA) optical microscope. Three types of metals, Ag, Al, and Au, were compared, and an 181-fold enhancement of CL emission was achieved with Ag nanoparticles (NPs), with the plasmon resonance wavelength close to the emission wavelength energy of ZnO. The enhanced emission is plausibly attributed to LSP/exciton coupling. However, it is also attributed to an increase in coupling efficiency with penetration depth and also to an increase in light extraction efficiency by grading the refractive indices at the heterostructure.

DC current sensor based upon a fused fiber optic Fabry-Perot interferometer (FPI) and copper wire

In order to meet the demand for direct current (DC) current measurements in industrial production, a new type of fiber optic DC current sensor, combining thin copper wire and fiber optic Fabry-Perot interferometer (FPI), is reported. FPI is a sandwich structure formed by splicing a single-mode fiber (SMF) and a quartz capillary, with a cavity length of approximately 200 μm. The copper wire, with a length of 3.2 cm and a diameter of 1 mm, is attached to the FPI to form the sensor. Due to the excellent thermal conductivity of copper, the results showed that the sensor increased the sensitivity from 4.1 pm/°C to 11 pm/°C. After applying direct current to the sensor, a large quantity of heat generated by the copper wire was absorbed by the FPI, resulting in a significant shift in the resonant wavelength of FPI, which can indirectly measure the current. Three current experiments were performed, and parabolic curves have been used in fitting of the Dip wavelength and the square of the current. The results provide high correlation coefficients with values exceeding 0.99. Therefore, this curve may be used to measure the square of the current, further obtaining the current. In summary, the sensor is compact and durable, easy to manufacture, and provides high correlation coefficients, providing an alternative for measuring DC current.

Selective-wavelength perfect infrared absorption in Ag@ZnO conical metamaterial structure

We present a new selective Metamaterial Perfect Absorber (MPA) consisting of zinc oxide embedded silver (Ag@ZnO), designed for applications in infrared stealth technology. The numerical simulation included a wide frequency range from 1 to 1000 THz and shows that the design MPA structure presented two absorption peaks at the desired wavelengths of 1.7 µm and 6.5 µm. The absorptivity of both peaks reached approximately 93.1% and 93.5%. The first peak at 1.7 µm decreases the scattering of IR laser beams from the surface of the MPA structure and also lowers the infrared tracks that could direct laser-guided devices to its specific target. On the other hand, the second peak reduces the surface heat wave. The suggested MPA (Ag@ZnO) structure is activated by a plane wave using a full wave vector and a broad frequency domain solution. In the framework of computer simulation technology (CST) Microwave Studio, uses both Finite-Difference-Time-Domain (FDTD) and Finite-Element-Method (FEM) techniques to predict the optical behavior of the proposed MPA structure. Both peaks achieved a high value of absorptivity due to the simultaneous excitation of the electric and magnetic dipole at resonance wavelength.

Graphene-functionalized photonic crystal fibers for detecting the refractive index of a wide range of analyzes

This study looks into a new photonic crystal fiber (PCF) sensor covered in graphene that can detect changes in the analyte's refractive index (RI) in the COMSOL environment. The sensor operates by detecting a peak in light loss that varies in wavelength based on the RI of the analyte. Higher RI analytes shift the peak towards longer wavelengths. It is explored how many factors affect the sensor's performance, such as graphene's Fermi energy, the site inside the fiber, and the thickness of the gold layer. The location of graphene and its Fermi energy have a substantial influence on how the sensor responds. Interestingly, the resonant wavelength has a linear relationship with the RI of the analyte, which allows for precise RI calculation. Increasing gold thickness improves light-material interaction, but subsequent thickening has a detrimental impact, lowering sensor sensitivity. The appropriate thickness varies according to the material under consideration. Finally, the analysis determines the optimal arrangement of graphene for maximum sensitivity by completely covering the analyte holes in the PCF. By finding the right balance between these factors, the suggested sensor can have both high spectral sensitivity and low sensor resolution.

Simple and reversible method to control the surface energy of ITO branched nanowires for tuning wettability of micro/nanoscale droplets

Reversible control of hydrophobic and hydrophilic surfaces has gained attention due to their potential applications in microfluidic devices, membranes for electrochemical cells, and sensors. While external stimuli such as temperature and electric field can regulate surface properties, they cannot be selectively applied to specific regions, which limits the patterning of areas with different surface energies. Here, we present a simple and reversible method for converting hydrophobic and hydrophilic properties through surface treatments involving nonpolar (−CFx) or polar groups (–OH) on indium tin oxide branched nanowires (ITO BRs). The formation of nonpolar groups results in superhydrophobic surface. Subsequent ultraviolet ozone treatment, using a shadow mask, induces the exposed area to transition into a superhydrophilic state, while the unexposed area retains superhydrophobicity. This demonstrates the potential for selective-area surface energy patterning. Furthermore, we investigate the wetting behavior of nanoscale Ag nanoparticles (NPs) on surface-modified ITO BRs. It is observed that size and shape of Ag NPs depend on the surface energy of ITO BRs. Consequently, controlling the surface energy leads to the formation of unique geometric structure of Ag NPs, enhancing plasmonic light absorption and scattering at specific resonant wavelengths.

Controllable dual resonances of Fano and EIT in a graphene-loaded all-dielectric GaAs metasurface and its sensing and slow-light applications

Abstract Active nanophotonic metasurfaces have attracted considerable attention for their promise to develop compact, tunable optical metadevices with advanced functions. In this work, we theoretically demonstrated the dynamically controllable dual resonances of Fano and electromagnetically induced transparency (EIT) using a graphene-loaded all-dielectric metasurface with U-shaped gallium arsenide (GaAs) nanobars operating in the near-infrared region. The destructive interference between a subradiant mode (i.e., a dark mode) supported by two vertical GaAs bars and two radiative modes (i.e., two bright modes) supported by a horizontal GaAs nanobar gives rise to a Fano resonance and an EIT window with high transmission and a large quality factor (Q-factor) in the transmission spectrum. Importantly, the transmission amplitudes can be flexibly modulated by adjusting the graphene Fermi levels without rebuilding the nanostructures. This modulation results from the controllable light absorption by the loaded graphene monolayer due to its interband losses in the near-infrared spectrum. Furthermore, the peak wavelengths of the Fano resonance and EIT window with high Q-factors are highly sensitive to variations in the refractive index (RI) of the surrounding medium, giving the proposed metasurface a relatively good sensitivity of ~700 nm/RIU and a high figure of merit (FOM) of 280, making it an effective RI sensor. Additionally, the metasurface features an adjustable slow light effect, indicated by the adjusted group delay time ranging from 0.12 ps to 0.38 ps. Therefore, the metasurface system proposed in this work offers a viable platform for advanced multi-band optical sensing, low-loss slow light devices, switches, and potential applications in nonlinear optical fields.

Cascade amplification-based triple probe biosensor for high-precision DNA hybridization detection of lung cancer gene

As an essential biomarker for diagnosing and treating various diseases, low-cost, quantitative detection methods for complementary DNA (cDNA) have received much attention. The surface plasmon resonance (SPR) sensing technique is an effective measurement scheme, but the ambient temperature and pH variations have a non-negligible impact. In this work, we developed a triple-probe SPR sensing system for detecting cDNA concentration, temperature, and pH. In order to satisfy the triple parameter measurements, we used a microstructured optical fiber as the sensing platform, silver and gold films as the excitation layer, and a MoS2 film as the modulation layer. First, we explore the modulation mechanism of SPR and the conditions for excitation of triple SPR and demonstrate that the carrier concentration is a crucial factor affecting the resonance wavelength. Then, the feasibility of the sensing system for triple-probing is theoretically analyzed. Finally, in the experiment, the optimal parameters of the sensor were determined, and the triple parameter detection was successfully realized. The experimental results show that the three probes can work independently, and the hybridized DNA probe can realize the selective detection of cDNA with a sensitivity of 0.249 nm/(nmol/l). The maximum sensitivity of the pH probe and the temperature probe are 51.5 nm/pH and 6.14 nm/°C. In addition, the experimental results show that the sensing probes have excellent reproducibility. This paper’s innovation is using the fiber optic SPR effect to achieve quantitative detection for cDNA, temperature detection, and pH detection. Therefore, the sensor has a promising future in early diagnosis and biosensing.

Towards higher frequencies in a compact prebunched waveguide THz-FEL

Free-electron-lasers fill a critical gap in the space of THz-sources as they can reach high average and peak powers with spectral tunability. Using a waveguide in a THz FEL significantly increases the coupling between the relativistic electrons and electromagnetic field enabling large amounts of radiation to be generated in a single passage of electrons through the undulator. In addition to transversely confining the radiation, the dispersive properties of the waveguide critically affect the velocity and slippage of the radiation pulse which determine the central frequency and bandwidth of the generated radiation. In this paper, we characterize the spectral properties of a compact waveguide THz FEL including simultaneous lasing at two different frequencies and demonstrating tuning of the radiation wavelength in the high frequency branch by varying the beam energy and ensuring that the electrons injected into the undulator are prebunched on the scale of the resonant radiation wavelength.

Fine-Tuning of Optical Resonance Wavelength of Surface-Micromachined Optical Ultrasound Transducer Arrays for Single-Wavelength Light Source Readout.

This article reports the fine-tuning of the optical resonance wavelength (ORW) of surface-micromachined optical ultrasound transducer (SMOUT) arrays to enable ultrasound data readout with non-tunable interrogation light sources for photoacoustic computed tomography (PACT). Permanent ORW tuning is achieved by material deposition onto or subtraction from the top diaphragm of each element with sub-nanometer resolution. For demonstration, a SMOUT array is first fabricated, and its ORW is tuned for readout with an 808 nm laser diode (LD). Experiments are conducted to characterize the optical and acoustic performances of the elements within the center region of the SMOUT array. Two-dimensional and three-dimensional PACT (photoacoustic computed tomography) is also performed to evaluate the imaging performance of the ORW-tuned SMOUT array. The results show that the ORW tuning does not degrade the optical, acoustic, and overall imaging performances of the SMOUT elements. As a result, the fine-tuning method enables new SMOUT-based PACT systems that are low cost, compact, powerful, and even higher speed, with parallel readout capability.