Optical Response Research Articles

Signature of excitonic insulators in phosphorene nanoribbons.

Phosphorene is a recently developed two-dimensional (2D) material that has attracted tremendous attention because of its unique anisotropic optical properties and quasi-one-dimensional (1D) excitons. We use first-principles calculations combined with the maximally localized Wannier function tight binding Hamiltonian (MLWF-TB) and Bethe-Salpeter equation (BSE) formalism to investigate quasiparticle effects of 2D and quasi-1D blue and black phosphorene nanoribbons. Our electronic structure calculations shows that both blue and black monolayered phases are semiconductors. On the other hand black phosphorene zigzag nanoribbons are metallic. Similar behavior is found for very thin blue phosphorene zig-zag and armchair nanoribbon. As a general behavior, the exciton binding energy decreases as the ribbon width increases, which highlights the importance of quantum confinement effects. The solution of the BSE shows that the blue phosphorene monolayer has an exciton binding energy four times higher than that of the black phosphorene counterpart. Furthermore, both monolayers show a different linear optical response with respect to light polarization, as black phosphorene is highly anisotropic. We find a similar, but less pronounced, optical anisotropy for blue phosphorene monolayer, caused exclusively by the quasi-particle effects. Finally, we show that some of the investigated nanoribbons show a spin-triplet excitonic insulator behavior, thus revealing exciting features of these nanoribbons and therefore provides important advances in the understanding of quasi-one dimensional phosphorus-based materials.&#xD.

Photoinduced carrier transfer dynamics in a monolayer MoS2/PbS quantum dots heterostructure

Two-dimensional molybdenum disulfide (MoS2) has been proven to be a candidate in photodetectors, and MoS2/lead sulfide (PbS) quantum dots (QDs) heterostructure has been used to expand the optical response wavelength of MoS2. Time-resolved pump-probe transient absorption measurements are performed to clarify the carrier transfer dynamics in the MoS2/PbS heterostructure. By comparing the carrier dynamics in MoS2 and MoS2/PbS under different pump wavelengths, we found that the excited electrons in PbS QDs can transfer rapidly (<100 fs) to MoS2, inducing its optical response in the near-infrared region, although the pump light energy is lower than the bandgap of MoS2. Besides, interfacial excitons can be formed in the heterostructure, prolonging the lifetime of the excited carriers, which could be beneficial for the extraction of the carriers in devices.

High-accuracy optical vector network analyzer for optical notch and bandpass responses

High-accuracy optical vector network analyzer for optical notch and bandpass responses

Symmetry breaking in 2D materials for optimizing second-harmonic generation

Abstract Second-harmonic generation (SHG) is the generation of 2ω (or half wavelength) light from incident light with frequency ω as a nonlinear optical response of the material. Three-dimensional (3D) SHG materials are widely investigated for developing laser technology to obtain shorter wavelengths in photolithography fabrication of semiconductor devices and the medical sciences, such as for imaging techniques that do not use fluorescent materials. However, to obtain the optimized SHG intensity, the 3D material is required to have no spatial-inversion symmetry (or non-centrosymmetry) and special crystal structure (or so-called phase-matched condition). Recently, engineering symmetry breaking of thin two-dimensional (2D) materials whose 3D structure has the inversion symmetry can offer a breakthrough to enhance the SHG intensity without requiring the phase-matched condition. Over the past decade, many 2D SHG materials have been synthesized to have broken inversion symmetry by stacking heterostructures, twisted moire structures, dislocated nanoplates, spiral nanosheets, antiferromagnetic order, and strain. In this review, we focus on the recent progress in breaking inversion and rotational symmetries in out-of-plane and/or in-plane directions. The theoretical calculations and experimental setup are briefly introduced for the non-linear optical response of the 2D materials. We also present our perspectives on how these can optimize the SHG of the 2D materials.

GOLD PLASMONIC ARRAY STRUCTURES FOR SENSING APPLICATIONS

This article is devoted to the theoretical study of the plasmonic properties of periodically arranged arrays of gold nanoparticles. The Comsol Multiphysics software, which is based on the finite element method, was used to build 3D numerical models for the simulation and conduct research. In this work the electric field distribution and optical characteristics of the spherical gold nanoparticles array were studied. Individual localized surface plasmon resonance modes are influenced when metallic nanoparticles are in the close proximity and as a result the electric near- fields can couple, resulting in a new hybrid mode. We mainly focused here on the investigation of two crucial questions, particularly, influences of the gap between the nanoparticles and the refractive index of the surrounding medium on the resulting optical response of the gold nanoparticles arrays. The array of periodically arragement gold nanoparticles is characterized by an enhanced local electric field between the nanoparticles, which is inversely proportional to the gap between the particles. The field strength and optical properties (reflection, transmission, and absorption) can be conveniently manipulated by changing the gap between particles. In additional, their potential applications as sensetive plasmonic sensors element have been considered. The studied structure has a significant potential for practical applications due to its wide range of the operating wavelengths and ease of the high-throughput fabrication. In the course of the study, it was established that the change in the distance between the surface of nanoparticles by 1 nm leads to a significant shift in the spectral transmission and reflection curves on the spectral range. In addition, these studies showed that an increase in the distance between the surfaces of nanoparticles leads to the decrease in the near-field interaction between gold nanoparticles in the array. Therefore, the obtained results can be successfully used in the manufacture of highly sensitive plasmon sensors with the possibility of controlling the sensitivity and the working spectral range.

Computational Evaluation of the Structural, Topological, and Solvent Effects on the Nonlinear Optical Properties of 1-Methylurea Butanedioic Acid Crystal

In silico investigation of the effects of a molecule’s framework and surroundings on its nonlinear optical (NLO) response is still an active topic of study in the fields of photonics and optoelectronics. NLO materials play a crucial role in modern photonics and optoelectronic technologies. Presented here is a comprehensive theoretical analysis of the structural, topological, and NLO features of 1-methylurea butanedioic acid (MUBA) alongside solvent effects (water, DMSO, and benzene) using the DFT method at the B3LYP(D4)/6–311++G(d,p) level. Geometric and infrared parameters were calculated and compared with experimental values. The analysis using atoms in molecules (AIM) and the independent gradient model (IGM) reveals the presence of two noncovalent intermolecular interactions: N4–H16⋯O12 and O6–H25⋯O3, which stabilize the crystal structure. The natural bond orbital (NBO) analysis reveals that the LP(1)N4 ⟶ π∗(C2-O3) interaction is the most stabilizing and is enhanced in solvent environments. NLO data show that the first (βtot) and second (γ) hyperpolarizability values of MUBA are approximately 0.6–1.1 and 8.3–17.0 times higher than those of urea. In addition, the quadratic and cubic responses of MUBA are significantly reduced and increased, respectively, in solvent environments. Based on its NLO susceptibilities, MUBA exhibits SHG, EOPE, OKE, and EFISHG properties, suggesting its potential application in the production of optoelectronic devices and optical limiting. This study enhances our understanding of the factors influencing the NLO behaviour of organic crystals, providing valuable insights for designing materials with enhanced NLO characteristics. The implications extend to industries such as telecommunications and computing, where faster data transmission rates are in high demand.

Terahertz and Infrared Plasmon Polaritons in PtTe2 Type-II Dirac Topological Semimetal.

Surface plasmon polaritons (SPPs) are electromagnetic excitations existing at the interface between a metal and a dielectric. SPPs provide a promising path in nanophotonic devicesforlight manipulation at the micro and nanoscale with applications in optoelectronics, biomedicine, and energy harvesting. Recently, SPPs have been extended to unconventional materials like graphene, transparent oxides, superconductors, and topological systems characterized by linearly dispersive electronic bands. In this case, three-dimensional Dirac and Weyl semimetals offer a promising frontier for infrared (IR) and terahertz (THz) radiation tuning by topologically-protected SPPs.In this work, we investigate the THz-IR optical response, of platinum ditelluride (PtTe2) type-II Dirac topological semimetal films grown on Si substrates. We detect SPPs generated on microscale ribbon arrays of PtTe2in the far-field limit,finding an excellent agreement among measurements, theoretical model, and electromagnetic simulation data.The far-field measurements have been further supported by near-field infrared data which indicate a strong electric field enhancement due to the SPP excitation near the ribbon edges. The whole results of this paper, indicate that PtTe2ribbon array appears an idealactive layout for geometrically tunable SPPs thus inspiring a new fashion of optically tunable materials in the technologically demanding THz and IR spectrum. This article is protected by copyright. All rights reserved.

DNA Origami‐Directed Self‐Assembly of Gold Nanospheres for Plasmonic Metasurfaces

AbstractPlasmonic nanostructures are frequently utilized to create metasurfaces with a large variety of optical effects. Control over shape and positioning of the nanostructures is key to the function of such plasmonic metasurfaces. Next to lithographic means, directed self‐assembly is a viable route to create plasmonic structures on surfaces with the necessary precision. Here, a combined approach of DNA origami self‐assembly and electron beam lithography is presented for determinate positioning of gold nanospheres on a SiO2 surface. First, DNA origami structures bind to the electron beam‐patterned substrate and subsequently, gold nanoparticles attach to a defined binding site on the DNA origami structure via DNA hybridization. A sol‐gel reaction is then used to grow a silica layer around the DNA, thereby increasing the stability of the self‐assembled metasurface. A mean yield of 74% of single gold nanospheres is achieved located at the determinate positions with a spatial position accuracy of 9 nm. Gold nanosphere dimers and trimers are achieved with a rate of 65% and 60%, respectively. The applicability of this structuring method is demonstrated by the fabrication of metasurfaces whose optical response can be tuned by the polarization of the incoming and the scattered light.

Superalkalides based on stacked janus molecule with improved optical nonlinearity

Research is actively being carried out to design new materials with exceptional nonlinear optical (NLO) responses. In this context, a systematic investigation of designing novel hypothetical materials e.g., superalkalides based on stacked Janus dimer, all-cis-1,2,3,4,5,6-hexafluorocyclohexane (C6H6F6)2 has been reported using high-level density functional simulations. The superalkalides are designed here by doping alkali metals on the fluorine face and superalkalis on the hydrogen face of Janus dimer. The thermodynamic stability of newly designed complexes is demonstrated by the interaction energies (Eint), ranging between −13.64 and −33.12 kcal/mol. Moreover, the superalkalide nature of these complexes is proved by negative charge and HOMO on superalkalis in natural bond orbitals (NBO) and frontier molecular orbitals (FMO) analyses, respectively. Energy gaps (Eg) between HOMO and LUMO orbitals of the designed complexes lie in the range of 0.63–0.83 eV. UV–Vis analysis is performed to gain idea about the transparent region of electromagnetic spectrum for nonlinear activity. The nonlinear activity of the designed superalkalide(s) is studied by static first hyperpolarizability β0, dynamic first hyperpolarizability β(ω) and dynamic second hyperpolarizability γ(2- ω; ω, ω). The highest β0, β(ω), and γ(2- ω; ω, ω) ranges up to 1.1 × 107, 2.9 × 106 and 2.9 × 1012 au, respectively for designed complexes. A comprehensive examination of these superalkalides based on stacked Janus dimers with exceptionally high NLO response highlights their potential for use in nonlinear optical materials.

First-principles screening of optoelectronics and thermoelectric response of XAcTe2 (X=K, Rb) full Heusler alloys: mBJ+SOC effect

Structural geometry, Electronic, optical, and thermoelectric attributes of XAcTe2 (X=K,Rb) full Heuser alloys were investigated theoretically via density functional theory (DFT). Structural optimization yielded optimized lattice parameters along with obtained negative formation energies (Ef) revealed the thermodynamically stable cubic geometries of alloys under investigation. For both alloys, the computed electronic band dispersions exhibit semiconductor behavior with a direct band gap. The band gap value of KAcTe2 is 1.59 eV, and 1.66 eV for RbAcTe2. The analysis of optical response shows maximum absorption α (ω) in the ultraviolet (UV) region, validating their quality for photovoltaic devices. The investigation of thermoelectric characteristics showed that both alloys display higher electrical conductivities and lower thermal conductivities.

Ab initio-simulated optical response of hot electrons in gold and ruthenium

Optical femtosecond pump-probe experiments allow to measure the dynamics of ultrafast heating of metals with high accuracy. However, the theoretical analysis of such experiments is often complicated because of the indirect connection of the measured signal and the desired temperature transients. Establishing such a connection requires an accurate model of the optical constants of a metal, depending on both the electron temperature T e and the lattice temperature T l . In this paper, we present first-principles simulations of the two-temperature scenario with T e ≫ T l , showing the optical response of hot electrons to laser irradiation in gold and ruthenium. Comparing our simulations with the Kubo-Greenwood approach, we discuss the influence of electron-phonon and electron-electron scattering on the intraband contribution to optical constants. Applying the simulated optical constants to the analysis of ultrafast heating of ruthenium thin films we highlight the importance of the latter scattering channel to understand the measured heating dynamics.

Optical non-linearities and applications of ZnS phosphors

Optical non-linearities play a crucial role in enabling efficient and ultrafast switching applications that are essential for next-generation photonic devices. ZnS phosphor material produces the best results in terms of increased luminescence quantum yield when doped with certain impurities. Nevertheless, the investigation of the third-order non-linear optical susceptibility of the phosphor materials can be exploited for various switching applications. In this regard, we review the recent advancements in the investigation of non-linear optical properties of ZnS phosphors, where the knowledge of absorption and refraction is utilized in various optical and detector applications. Furthermore, the review highlights strategies employed to enhance the non-linear optical response of phosphor materials as well as a general discussion of an attosecond optical switching scheme which can be used to fabricate devices with petahertz speeds. Consequently, we provide a solution to the unsolved problem of the significant extension of optical limiting applications to switching applications by developing design strategies to manipulate conventional ZnS phosphor material. The potential challenges and future prospects of utilizing phosphor materials for switching applications are also addressed. The strategies for manipulating ZnS phosphor can be generalized for a broad range of other materials by minimizing linear and non-linear losses, while enhancing the values of the non-linear refractive index coefficient. We propose that the figure-of-merit of ZnS material can be enhanced by using a suitable combination of pump and probe wavelength values, which can be useful for optical switching applications.

Giant Terahertz Birefringence in an Ultrathin Anisotropic Semimetal.

Manipulating the polarization of light at the nanoscale is key to the development of next-generation optoelectronic devices. This is typically done via waveplates using optically anisotropic crystals, with thicknesses on the order of the wavelength. Here, using a novel ultrafast electron-beam-based technique sensitive to transient near fields at THz frequencies, we observe a giant anisotropy in the linear optical response in the semimetal WTe2 and demonstrate that one can tune the THz polarization using a 50 nm thick film, acting as a broadband wave plate with thickness 3 orders of magnitude smaller than the wavelength. The observed circular deflections of the electron beam are consistent with simulations tracking the trajectory of the electron beam in the near field of the THz pulse. This finding offers a promising approach to enable atomically thin THz polarization control using anisotropic semimetals and defines new approaches for characterizing THz near-field optical response at far-subwavelength length scales.

Stretchable metal–dielectric–metal metasurface for dynamic radiation management

Radiative cooling devices offer passive characteristics and hold significant potential for reducing energy consumption. However, to address changing climate needs, dynamic devices with tunable radiation properties are crucial. Here, we propose a novel, to the best of our knowledge, design for tunable radiative thermal management utilizing a reconfigurable flexible metasurface emitter. By applying biaxial stretching to alter the metasurface’s periodicity, its optical response can be continuously modulated. At ambient temperature, with a stretch ratio of 1.6, the device is predicted to achieve thermal management power modulations of 173W/m2 and 42W/m2 during daytime and nighttime, respectively. This approach holds promise for improving the efficiency of thermal management systems in applications such as buildings and smart windows.

Investigating the Z-scan technique for quantifying circulating cell-free DNA (ccfDNA) extracted from blood plasma as a potential biomarker for various cancers.

Abstract
The Z-scan technique is a nonlinear optical method that has found applications in characterizing various materials, particularly those exhibiting nonlinear optical response (NLOR). This study applies the continuous wave (CW) Z-scan technique to examine the NLOR in terms of the nonlinear optical phase shifts (ΔΦ_0) exhibited by the ccfDNA extracted from blood plasma samples collected from a group constituting 30 cancer-diagnosed patients and another group constituting 30 non-diagnosed individuals. The cancer group exhibited significantly higher ΔΦ_0vs. incident power slopes compared to the non-cancer group (0.34 vs 0.12) providing a clear distinction between the two groups. The receiver operating characteristic (ROC) curve analysis of the results indicates a clear separation between cancer and non-cancer groups, along with a 94% accuracy rate of the data. The Z-scan results are corroborated by spectrophotometric analysis, revealing a consistent trend in the concentration values of ccfDNA samples extracted from both cancerous and non-cancerous samples, measuring 3.24 and 1.41 respectively. Additionally, more sensitive fluorometric analyses of the respective samples demonstrate significantly higher concentrations of ccfDNA in the cancer group, further affirming the correlation with the Z-scan results. The study suggests that the Z-scan technique holds promise as an effective method for cancer detection, potentially contributing to improved oncology diagnosis and prognosis in the future.&#xD.

Floatable Cu2(OH)PO4/rGO Aerogel for Full Spectrum Driven Photocatalytic Degradation of Organic Pollutants.

Photocatalytic technology is an attractive option for environmental remediation because of its green and sustainable nature. However, the inefficient utilization of solar energy and powder morphology currently impede its practical application. Here, we designed a floatable photocatalyst by anchoring 0D Cu2(OH)PO4 (CHP) nanoparticles on 2D graphene to construct 0D/2D CHP/reduced graphene oxide (rGO) aerogels. The CHP/rGO aerogels have interconnected mesopores that provide a large surface area, promoting particle dispersion and increasing the number of active sites. Moreover, the optical response of the CHP/rGO aerogel has been significantly expanded to cover the full spectrum of the solar light. Notably, the 20%CHP/rGO aerogel displayed a high degradation rate (k = 0.178 min-1) taking methylene blue (MB) as a model pollutant under light irradiation (λ > 420 nm). The enhanced photocatalytic activity is ascribed to the rapid electron transfer in the CHP/rGO heterostructures, as supported by the DFT theoretical calculations. Our research highlights the utilization of full spectrum responsive photocatalysts for the elimination of organic pollutants from wastewater under solar light irradiation, as well as the potential for catalyst recovery using floatable aerogels to meet industrial requirements.

Insights on the effect of process conditions on the optical properties of silver ion exchanged soda-lime silicate glass

The effects of ion exchange time and temperature on the optical properties and plasmonic response of silver ion exchanged soda-lime silicate glass were investigated using scanning electron microscopy (SEM) in energy dispersive spectrometry (EDS) configuration, m-lines spectroscopy, photoluminescence (PL) spectroscopy, and UV–visible absorption spectroscopy. SEM analyses in EDS mode provided profiles of silver oxide molar concentration. These profiles were directly correlated to the silver diffusion coefficient using an adjustment procedure. The effective indices of ion exchanged glasses measured by the standard prism coupling technique (m-lines) allowed access to refractive index distributions in ion exchange regions. These ion-exchanged glasses underwent evaluation to determine their potential suitability for use in multimode planar systems. The PL results acquired after ion exchange demonstrated that the creation of Ag0 atoms from Ag+ ions was responsible for the decline and quenching of PL intensity at ion exchange times and temperatures increase. Silver nanoparticles were generated in the samples subjected to ion exchange at 480 °C without the need for post-exchange treatments. The emergence of the surface plasmon resonance band around 427 nm in the optical absorption spectra confirmed the formation of Ag nanoparticles in annealed glasses. Estimates of the UV–visible absorption spectra indicated an average size of silver nanoparticles ranging from 1.8 to 2.4 nm.

Optical tunability with superlattice hyperbolic metamaterial coatings

Optical tunability is demonstrated with multi-metal hyperbolic metamaterial (HMM) structures on varying substrate surfaces. A systematic uniaxial modeling methodology is adapted from classical approaches to extract the anisotropic permittivity of the films to identify epsilon-near-zero (ENZ) behavior over a wide range of metal volume fractions (φ). The anisotropic model accuracy is quantified by a mean squared error (MSE) with the presented modeling routine resulting in a MSE < 35 for all samples. The optical model thicknesses were verified with transmission electron microscopy (TEM) imaging and measurements. This study also demonstrates the ability to tune the optical responses in the visible-to-infrared frequencies with surface microtexturing and applied strain with HMM coatings on flexible Kapton substrates. Furthermore, the structured films and modeling procedure lay the groundwork for future studies on coupling the anisotropic optical and thermal properties for control over advanced multifunctional thin-film coatings.

Double Resonance Characteristic of Photonic Crystal Structure with Defect Metal Layer

The optical response of the photonic crystal structure has been analyzed using the Finite Difference Frequency Domain (FDFD) method. Simulation using this method aims to analyze the characteristics of light transmission when interacting with related structure. The results of the study of photonic crystal structures with two defects show that there are two transmittance bands called double resonances at two specific wavelengths. Changes in the resonance peak with respect to the variations of refractive index in the second defect layer resulted in a linear change with significant sensitivity. For photonic crystals with two defects, the first defect is a metal layer and the second defect is material sensing, which produces double resonance with a sensitivity of 7,825 and 3,2675, while for photonic crystals with the first defect, a dielectric layer, and the second defect is material sensing, produces single resonance with a sensitivity of 2,022. The choice of the first defect is that the metal layer is quite important, in addition to producing greater sensitivity, it also produces a field enhancement between the dielectric and the metal layer which is called surface plasmon resonance (SPR). The sensitivity value can also be set by determining the thickness of the second defect layer. These results can be used as a standard for fabrication and developed for sensor applications.

Angle-Resolved Polarimetry with Quasi-Bound States in the Continuum Plasmonic Metamaterials via 3D Aerosol Nanoprinting.

Three-dimensional (3D) plasmonic metamaterials, featuring well-arranged subwavelength nanostructures, facilitate effective coupling between electrical dipoles and incident electromagnetic waves. This coupling allows for unique optical responses including localized surface plasmon resonance (LSPR) and quasi-bound states in the continuum (q-BIC). While 3D plasmonic metamaterials with LSPR and q-BIC have been independently explored for sensors, achieving simultaneous optical responses in the near-infrared region remains challenging. Here, we present 3D plasmonic metamaterials that integrate LSPR and q-BIC within a single π-shaped plasmonic structure, fabricated using a 3D aerosol nanoprinting technique. This printing technique controls the local electrostatic field to precisely position charged metallic nanoaerosols, enabling parallel printing of π-shaped plasmonic structures under ambient conditions. The printed π-shaped plasmonic structures exhibit two distinct optical modes: x-polarization-sensitive LSPR and transverse magnetic mode-sensitive q-BIC within the near-infrared region. Exploiting these dual optical responses, we demonstrate simultaneous polarization detection and incident angle analysis by integrating the π-shaped plasmonic structures into commercial Fourier-transform infrared spectroscopy, termed "numerical aperture-detective polarimetry". This approach holds promise for evaluating alignment in optical and imaging systems with light distribution analysis. Furthermore, the 3D aerosol nanoprinting technique provides an avenue for fabricating 3D plasmonic metamaterials with intricate geometries and optical properties, expanding their potential applications in nano-optics.