Ultra-narrow Absorption Research Articles

THz Biosensing for Early Detection of Influenza and Coronaviruses Using Dielectric Metamaterials

Abstract The world has faced a significant challenge since December 2019, when coronavirus (COVID-19) was found. Viruses of this type are causing pandemics all over the world right now. For this purpose, a biosensor is designed to operate based on metamaterial (MM) incorporated and can detect different coronaviruses. The proposed metamaterial absorber (MMA) includes two bands that have perfect absorption characteristics and a very narrow absorption bandwidth: 4.093 THz and 3.647 THz. The circuit model's transmission line technique is another approach to verifying the absorber's functionality. The proposed design consists of a square-shaped graphene ring (SGR) and a silicon-based square ring resonator (SSRR) to provide unique and narrow band absorption characteristics. Changing the graphene’s chemical potential gives the suggested MMA tuneability and control capability. The suggested MMA can detect several coronaviruses because of its extremely narrow absorption spectrum behavior. It has unique features such as ultra-narrow absorption bandwidth, polarization insensitivity, and simplicity. The MMA is designed with a compact structure, good sensitivity (s), exceptional Figure of Merit (FOM), and superior Quality factor (Q) values.

Toward liquid cell quantum sensing: Ytterbium complexes with ultranarrow absorption.

The energetic disorder induced by fluctuating liquid environments acts in opposition to the precise control required for coherence-based sensing. Overcoming fluctuations requires a protected quantum subspace that only weakly interacts with the local environment. We report a ytterbium complex that exhibited an ultranarrow absorption linewidth in solution at room temperature with a full width at half maximum of 0.625 milli-electron volts. Using spectral hole burning, we measured an even narrower linewidth of 410 pico-electron volts at 77 kelvin. Narrow linewidths allowed low-field magnetic circular dichroism at room temperature, used to sense Earth-scale magnetic fields. These results demonstrated that ligand protection in lanthanide complexes could substantially diminish electronic state fluctuations. We have termed this system an "atomlike molecular sensor" (ALMS) and proposed approaches to improve its performance.

Absorption enhancement in silicon-based dielectric resonator for quad-band terahertz biosensing

A technique is implemented to obtain the multi-band perfect absorption (nearly 100%) in an ultrathin silicon-based dielectric resonator (DR) using perturbation. A silicon-based plus-shaped resonator is utilized to design the proposed absorber which provides the four narrow-band absorptions at frequencies of around 5.75, 6.14, 6.48, and 7.24 THz with the level of absorption 54%, 20%, 95%, and 96%, respectively. The plus-shaped resonator is perturbed by cutting slot of plus shape in such a way that it obtains perfect absorption with sufficient guard-band to prevent the multi-band interference in each band. This perturbation provides four absorption peaks at frequencies of around 5.80, 6.27, 6.80, and 7.23 THz, with highly improved absorption in all the bands, i.e., 99.84%, 99.78%, 99.51%, 98.42%, respectively. The ultranarrow absorption peaks with narrow FWHM are suitable for the application of THz biosensing and refractive index analysis. The performance of the proposed absorber is studied with the variation in refractive index of sample. It is found that the proposed absorber provides the high sensitivity 0.186, 0.29, 0.2485, 0.43 THz RIU−1 and quality factor 280, 185.79, 320.42, and 131.51 for different bands, respectively. The proposed absorber performance is also studied for various THz biosensing applications like the detection of various viruses, malaria, and cancer in the human body at various stages.

Elucidating ultranarrow 2F7/2 to 2F5/2 absorption in ytterbium(iii) complexes.

Achieving ultranarrow absorption linewidths in the condensed phase enables optical state preparation of specific non-thermal states, a prerequisite for quantum-enabled technologies. The 4f orbitals of lanthanide(iii) complexes are often referred to as "atom-like," reflecting their isolated nature, and are promising substrates for the optical preparation of specific quantum states. To better understand the photophysical properties of 4f states and assess their potential for quantum applications, theoretical building blocks are required for rapid screening. In this study, an atomic-level perturbative calculation (i.e., spin-orbit crystal field, SOCF) is applied to various Yb(iii) complexes to investigate their linear absorption and emission through a fitting mechanism of their experimentally determined transition energies and oscillator strengths. In particular, the optical properties of (thiolfan)YbCl(THF) (thiolfan = 1,1'-bis(2,4-di-tert-butyl-6-thiomethylenephenoxy)ferrocene), a recently reported complex with an ultranarrow optical linewidth, are computed and compared to those of other Yb(iii) compounds. Through a transition energy sampling study, major contributors to the optical linewidth are identified. We observe particularly isolated f-f transitions and narrow linewidths, which we attribute to two distinct factors. Firstly, the ultra-high atomic similarity of the orbitals involved in the optical transition, along with the presence of an anisotropic crystal field, collectively contribute to the observed narrow transitions. Secondly, we note highly correlated excited-ground energy fluctuations that serve to greatly suppress inhomogeneous line-broadening. This article illustrates how SOCF can be used as a low-cost method to probe the influence of crystal field environment on the optical properties of Yb(iii) complexes to assist the development of novel lanthanide series quantum materials.

Tunable narrowband and broadband coexisting absorber enabled by a simple all-metal grating for sensing applications

We realize a tunable narrowband and broadband coexisting absorber based on a simple step-shaped all-metal grating structure. The absorber presents an ultra-narrow absorption band of 1.5 nm and a relatively broad absorption band of 29.8 nm, both with nearly 100% absorption in the infrared region. The mechanism underlying the dual-band perfect absorption is the interaction between two diffraction coupled surface plasmon polariton (SPP) modes with one of them modulated by a cavity resonance. Influences of structure parameters on the absorption performance are numerically investigated. It is found that the positions of the two perfect absorption peaks can be easily tuned both independently and together by changing the structural parameters. In addition, the designed grating structure presents excellent sensing performance with sensitivity and figure of merit as high as 2,514 nm/RIU and 1,600 RIU−1, respectively. The excellent sensing performance, flexible tenability and simple structure design endow this grating absorber with great potential in high-precision biochemical sensing applications.

Ultrathin, Ultra Narrow Band DMMA for Biosensing Applications.

A new ultrathin, ultra narrow band Dielectric based Metamaterial Absorber (DMMA) is designed for biosensing applications. The absorber provides dual-band response with perfect absorption with ultra-narrowband absorption characteristics with resonances at 5.98 THz and 6.72 THz. The absorber consists of a silicon based square split ring (SSSR) along with a graphene based circular split ring (GCSR) for the generation of perfect and ultra-narrow absorption characteristics. By varying the chemical potential of the graphene, the tunability and controllability is achieved for the proposed absorber. Due to its ultra narrow band absorption characteristics, the proposed absorber can be used for sensing cancer in various parts of the body, malaria, glucose in water and other chemicals. The unique features of the proposed absorber are its ultra-thin structure, simple design, tunability, polarization insensitivity, ultra narrow absorption bandwidth, high sensitivity, high Figure of Merit (FOM), and very high Quality factor (Q) values in a single device for detecting different diseases and chemicals.

Simple structured ultranarrow‐band metamaterial perfect absorber with dielectric‐dielectric‐metal configuration

AbstractA simple structured ultranarrow‐band metamaterial perfect absorber (MPA) with dielectric‐dielectric‐metal configuration is studied both theoretically and experimentally. By optimizing the dielectric connectivity layer and metal substrate, the optimized simple structured ultranarrow‐band MPA is obtained. Theoretical simulation results show that the MPA exhibits single ultranarrow absorption peak at normal incidence and double ultranarrow absorption peaks at oblique incidence. The heat power density distributions of the optimized MPA are also calculated to depict the absorption mechanism. At last, we fabricate a MPA sample and measure its absorption spectra to make a further comparison. The experimental data are consistent with the theoretical ones. This novel method might be helpful to reduce the manufacture difficulty and cost of the ultranarrow‐band MPAs, and also to promote the development of applications of the ultranarrow‐band MPAs.

Generating multiple resonances in ultrathin silicon for highly selective THz biosensing

A technique is implemented for achieving the multiband terahertz (THz) absorption with high-quality factor in an absorber containing an ultrathin silicon resonator. The symmetrical perturbation is done in the silicon layer for obtaining the multiple multi-order electric and magnetic resonances. The proposed absorber structure provides the polarization insensitive absorption spectrum with ten absorption peaks out of which seven remain with the level of more than 90%. The ultranarrow absorption spectrum can be utilized in THz biosensing applications specially for the detection of breast cancer, malaria in blood and glucose in water. It offers highest sensitivity as 0.416 THz/thickness unit (TU) and 1.02 THz/refractive index unit (RIU) during analyte thickness and refractive index sensing, respectively. The proposed absorber can provide the high value of quality factor along with all other improved parameters like sensitivity and figure of merit. Moreover, graphene nano-rings can also be utilized for obtaining the controllability in the frequency response of the absorber.

Ultranarrow perfect absorber with linewidth down to 1 nm based on optical anapole mode

This paper is investigated a silicon-dielectric-metal nanostructure, it supports the optional anapole mode due to the destructive interference between electric and toroidal dipoles. Such the proposed nanostructure exhibits a near-perfect ultra-narrow absorption spectrum in the near infrared region with the absorption bandwidth (FWHM) of 0.48 nm and a high-quality (Q) factor up to 1763. Besides inherently low dissipative losses and strong anapole response, this optical nanostructure can demonstrate subtle refractive index sensing properties. Our work shed new light on active ultra-narrow band perfect absorption based on the optical anapole mode, and provides potential applications such as optical sensors, narrow-band filter, non-radiative data transmission and biomolecules manipulation.

A five-band absorber based on graphene metamaterial for terahertz ultrasensing

We design and propose a five-band absorber based on graphene metamaterial for the terahertz (THz) sensing field. The localized surface plasmon resonances of patterned graphene are excited, contributing to five tunable ultra-narrow absorption peaks, which are specified by the electric field distributions. Moreover, the absorber is insensitive to different polarization modes and incident angles. When increasing the Fermi level of the patterned graphene, which is composed of a round ring and a square ring connected by four thin wires, the resonant frequencies exhibit distinct blue shifts. For refractive index sensing, due to the addition of a continuous dielectric groove, the theoretical results show that the maximum averaged normalized sensitivity, Q factor, and FOM can reach 0.647 RIU−1 (refractive index unit, RIU), 355.94, and 215.25 RIU−1, indicating that the sensing performances are further enhanced compared with previous works. As a result, the proposed structure may provide a new method to realize ultrasensing in the THz region.

TPP-assisted multi-band absorption enhancement in graphene based on Fibonacci quasiperiodic photonic crystal

The multi-channel enhanced absorption properties in graphene monolayer are theoretically studied. It is realized by inserting a graphene monolayer in a dielectric film, which is sandwiched between a metallic film and a Fibonacci quasiperiodic structure. It is shown that three peaks with absorbance above 75% can be achieved, which is attributed to the Tamm plasmon polaritons and multiple photonic stopbands of the Fibonacci dielectric multilayers. Moreover, the distribution of the normalized electric field intensity is simulated to reveal the physical origin of such multichannel absorption effect. The designed graphene absorber possesses ultra-narrow absorption profiles and performs similar to an antenna. Furthermore, the multichannel absorption performances could be flexibly tuned by changing the angle of the incident and the geometric dimensions. Our results may find potential applications in the design of novel photoelectronic devices.

Multi-resonant absorptions in asymmetric step-shaped plasmonic metamaterials for versatile sensing application scenarios.

Plasmonic nanostructures have attracted remarkable attention in label-free biosensing detection due to their unprecedented potential of high-sensitivity, miniaturization, multi-parameter, and high throughput screening. In this paper, we propose a plasmonic metamaterial absorber consisting of an asymmetrical step-shaped slit-groove array layer and an opaque gold film, separated by a silica dielectric layer, which demonstrates three-resonant perfect absorption peaks at near-infrared frequencies in an air environment.This is equivalent to three reflection dips due to the opaque gold membrane underneath the structure. Originating from the coupling and hybridization of different plasmonic modes, these three absorption peaks show different linewidths and distinctive excellent sensing performance. The surface lattice resonance (SLR) at the short wavelength range enables an ultra-narrow absorption peak of merely 2 nm and a high bulk refractive index sensitivity of 1605 nm/RIU, but occurring with comparatively low surface sensitivity. Compared to the above-mentioned narrowband SLR mode, the other two absorption peaks, respectively stemming from the coupling between slit-cavity mode and the plasmon resonance of different orders, possess relatively broad linewidths and low bulk refractive index sensitivities, yet outstanding surface sensitivities. The complementary sensing performance among these absorption peaks presents opportunities for using the designed plasmonic metamaterial absorber for multi-parameter detection and various complex application scenarios.

Slip-Stacked J-Aggregate Materials for Organic Solar Cells and Photodetectors.

Dye-dye interactions affect the optical and electronic properties in organic semiconductor films of light harvesting and detecting optoelectronic applications. This review elaborates how to tailor these properties of organic semiconductors for organic solar cells (OSCs) and organic photodiodes (OPDs). While these devices rely on similar materials, the demands for their optical properties are rather different, the former requiring a broad absorption spectrum spanning from the UV over visible up to the near-infrared region and the latter an ultra-narrow absorption spectrum at a specific, targeted wavelength. In order to design organic semiconductors satisfying these demands, fundamental insights on the relationship of optical properties are provided depending on molecular packing arrangement and the resultant electronic coupling thereof. Based on recent advancements in the theoretical understanding of intermolecular interactions between slip-stacked dyes, distinguishing classical J-aggregates with predominant long-range Coulomb coupling from charge transfer (CT)-mediated or -coupled J-aggregates, whose red-shifts are primarily governed by short-range orbital interactions, is suggested. Within this framework, the relationship between aggregate structure and functional properties of representative classes of dye aggregates is analyzed for the most advanced OSCs and wavelength-selective OPDs, providing important insights into the rational design of thin-film optoelectronic materials.

Ultraviolet graphene ultranarrow absorption engineered by lattice plasmon resonance

We numerically demonstrate an ultraviolet graphene ultranarrow absorption in a hybrid graphene-metal structure. The full-width at half maximum of the absorption band being 9 nm in ultraviolet range is achieved based on the coupling of lattice plasmon resonances of the metallic nanostructure to the optical dissipation of graphene. The position, absorbance and linewidth of the hybridized narrow resonant mode tuned by controlling geometrical parameters and materials are systematically investigated. The proposed structure possesses high refractive index sensitivity of 288 nm/RIU and figure of merit of 72, and can also be used to detect small molecules layer of sub-nanometer thickness and refractive index with small changes, providing promising applications in ultra-compact efficient biosensors.

Semitransparent Layers of Social Self‐Sorting Merocyanine Dyes for Ultranarrow Bandwidth Organic Photodiodes

AbstractTwo dipolar merocyanines consisting of the same π‐conjugated chromophore but different alkyl substituents adopt very different packing arrangements in their respective solid state with either H‐ or J‐type exciton coupling, leading to ultranarrow absorption bands at 477 and 750 nm, respectively, due to exchange narrowing. The social self‐sorting behavior of these push‐pull chromophores in their mixed thin films is evaluated and the impact on morphology as well as opto‐electronical properties is determined. The implementation of this well‐tuned two‐component material with tailored optical features allows to optimize planar heterojunction organic photodiodes with fullerene ​(C60) with either dual or single wavelength selectivity in the blue and NIR spectral range with ultranarrow bandwidths of only 11 nm (200 cm−1) and an external quantum efficiency of up to 18% at 754 nm under 0 V bias. The application of these photodiodes as low‐power consuming heart rate monitors is demonstrated by a reflectance‐mode photoplethysmography (PPG) sensor.

Tunable dual-band terahertz absorber with all-dielectric configuration based on graphene.

In this paper, we theoretically design a dual-band graphene-based terahertz (THz) absorber combining the magnetic resonance with a THz cold mirror without any metallic loss. The absorption spectrum of the all-dielectric THz absorber can be actively manipulated after fabrication due to the tunable conductivity of graphene. After delicate optimization, two ultra-narrow absorption peaks are achieved with respective full width at half maximum (FWHM) of 0.0272 THz and 0.0424 THz. Also, we investigate the effect of geometric parameters on the absorption performance. Coupled mode theory (CMT) is conducted on the dual-band spectrum as an analytic method to confirm the validity of numerical results. Furthermore, physical mechanism is deeply revealed with magnetic and electric field distributions, which demonstrate a totally different principle with traditional plasmonic absorber. Our research provides a significant design guide for developing tunable multi-resonant THz devices based on all-dielectric configuration.

High Performance Plasmonic Nano-Biosensor Based on Tunable Ultra-Narrowband Perfect Absorber Utilizing Liquid Crystal

In this paper, a refractive index plasmonic nano-sensor based on a tunable perfect absorber has been proposed in the near-infrared region. The proposed sensor consists of a truncated cone resonator with more than 99% absorption and ultra-narrow bandwidth. Liquid crystal has been used in the designed nano-structure to tune the structure by variation of the incident angle and applying the external bias field to obtain the near perfect and ultra-narrow absorption peak. The proposed nano-sensor has a high sensitivity of 1363.63 nm/RIU and a high figure of merit of 1136.36 RIU−1 at the telecommunication wavelength of 1550 nm. Furthermore, after obtaining appropriate conditions for the liquid crystal layer, we have suggested a new resonator to boost the interaction of surface plasmons and the test medium. Therefore, the sensitivity and figure of merit are increased to the values of 1509 nm/RIU and 1257.5 RIU−1, respectively. This excellent performance of the sensor has huge potential for precision applications such as biomedical science and biosensor. Hence, the capability of the proposed nano-sensor in the field of histopathology for cancerous tissue diagnosis and detection of toxic and flammable gases to prevent endangering human health has been studied. In this case, the high sensitivity of 1368.06 nm/RIU and high figure of merit of 1179.36 RIU−1 have been obtained.

Polarization-independent absorption enhancement in graphene for light incidence in conical mounting

A terahertz graphene tunable absorber consisting of monolayer graphene on a dielectric grating and a substrate separated by a waveguide layer is designed and investigated. The absorber exhibits polarization-independent absorption enhancement at resonance for fully conical light incidence, which is attributed to the simultaneous excitation of two identical guided modes in the waveguide layer. Moreover, the absorber possesses an ultranarrow absorption profile with an ultrahigh quality factor. To intuitively confirm the potential physical mechanism of such phenomena, the electromagnetic field distributions for both polarized light are described. Finally, the influences of Fermi level and relaxation time on the absorption properties are investigated, which present the flexible tunability of the proposed device. It is believed that the conclusions will enable the development of optoelectronic devices by simply combining graphene with a guided-mode resonance structure.

Ultra-narrowband dielectric metamaterial absorber for sensing based on cavity-coupled phase resonance

We propose an ultra-narrowband dielectric metamaterial absorber with dielectric-dielectric-metal (DDM) structure where a dielectric cavity layer is inserted between the top compound periodic dielectric microstructures and bottom metal substrate. The results show that this absorber has an ultra-narrowband absorption with a full width at half-maximum (FWHM) of 0.028 nm and quality factor larger than 50,000 in the near-infrared regime. The electric field distribution shows that the phase resonance excited in the microstructures slits is coupled with the cavity resonance occurring in the middle dielectric layer which can greatly narrow the absorption bandwidth. More importantly, the absorption bandwidth can be flexibly manipulated by adjusting the thickness of the dielectric cavity layer. Due to the ultra-narrow absorption bandwidths and electric field concentrated in the slits, we can get a huge figure of merit (FOM) of 6731 which is much larger than those of the reported absorbers in the near-infrared regime. In addition, the larger FOM of 20,366 can be attained with higher-order mode resonance in the dielectric cavity layer. The proposed metamaterials have the great potentials in sensing applications.

Ultra-narrowband dielectric metamaterial absorber with ultra-sparse nanowire grids for sensing applications

Due to their low losses, dielectric metamaterials provide an ideal resolution to construct ultra-narrowband absorbers. To improve the sensing performance, we present numerically a near-infrared ultra-narrowband absorber by putting ultra-sparse dielectric nanowire grids on metal substrate in this paper. The simulation results show that the absorber has an absorption rate larger than 0.99 with full width at half-maximum (FWHM) of 0.38 nm. The simulation field distribution also indicates that the ultra-narrowband absorption is originated from the low loss in the guided-mode resonance. Thanks to the ultra-narrow absorption bandwidths and the electric field mainly distributed out of the ultra-sparse dielectric nanowire grids, our absorber has a high sensitivity S of 1052 nm/RIU and a large figure of merit (FOM) of 2768 which mean that this ultra-narrowband absorber can be applied as a high-performance refractive index sensor.