Infrared Frequency Range Research Articles

Terahertz super-radiance from picosecond electron bunches moving through a micro-undulator

We suggest using emission from the photoinjector-formed electron bunches moving through micro-undulators for generation of powerful super-radiant pulses in the terahertz/far infrared frequency range. Within the time-domain quasi-optical approach, we demonstrate the spatial coherence of emission with narrow angular spectrum from the electron bunches with transverse size limited by the Fresnel parameter NF ∼ 1, when the diffraction effects together with slippage provide synchronization of radiation from the entire volume of the extended bunch. For picosecond-duration, 5 MeV, 250 pC electron bunches, and a micro-undulator with a period of 3 mm, the peak power of 15 THz SR pulses can be about of 20 MW.

Vanadate Crystals with an Enhanced Birefringence and a Broadened Transparency Spectrum through Controlled [VO3]∞ Chain Arrangements and Alkali Metal Cation Introduction.

The vanadate (VO) polyhedron offers a compelling avenue for exploring birefringent materials within the infrared frequency range. Among many potential building blocks, the implementation of [VO3]∞ chains demonstrated great potential as effective birefringent functional units. In this article, we successfully synthesized the Li0.8Na0.2CsV2O6·H2O compound, which exhibits a remarkable birefringence of 0.134 at 546.1 nm, as confirmed by the experiment. Notably, the introduction of alkali metals in this compound led to a significantly shorter cutoff edge at 340 nm. Through a comprehensive investigation, Li0.8Na0.2CsV2O6·H2O has the shortest UV cutoff edge among all vanadates, whose birefringences are larger than 0.1, to the best of our best knowledge. This finding underscores the application potential of this novel material as a birefringent crystal.

Polarization dependent light propagation in textrm{WTe}_2 multilayer structure

textrm{WTe}_2 is one of the exciting and outstanding semimetallic members of TMDCs, which has attracted immense attention for manipulating light propagation due to its inherent optical anisotropy and hyperbolic characteristic in the infrared frequency range. We investigate the dependence of the reflectance and transmittance of structures with a single and double textrm{WTe}_2 thin film in terms of frequency and polarization angle of the incident wave. We find rich behaviors in the optical response of these structures due to their anisotropic permittivity tensors. Furthermore, we analyze the polarization state of transmitted and reflected waves through these structures. We demonstrate that these structures provide the ability to achieve desired polarization rotation for outgoing waves by tuning the frequency and polarization angle of the incident wave with respect to the principal axes of textrm{WTe}_2 thin film. In particular, we elucidate the essential relevance of the optical response and polarization rotation of the double thin film structure to the in-plain twist angle of textrm{WTe}_2 thin films. We explain that this structure permits comprehensive control of the polarization rotation of the outgoing waves by adjusting the twist angle of thin films. The proposed structure can be employed as an efficient light manipulator with the aim of application in communication, imaging, and information processing.

Design of infrared optical absorber using silver nanorings array made by a top-down process

This paper presents the numerical simulation and fabrication of a metasurface composed of silver nanorings with a split-ring gap. These nanostructures can exhibit optically-induced magnetic responses with unique possibilities to control absorption at optical frequencies. The absorption coefficient of the silver nanoring was optimized by performing a parametric study with Finite Difference Time Domain (FDTD) simulations. The absorption and scattering cross sections of the nanostructures are numerically calculated to assess the impact of the inner and outer radii, the thickness and the split-ring gap of one nanoring, as well as the periodicity factor for a group of four nanorings. This showed full control on resonance peaks and absorption enhancement in the near infrared spectral range. The experimental fabrication of this metasurface made of an array of silver nanorings is achieved by e-beam lithography and metallization. Optical characterizations are then carried out and compared to the numerical simulations. In contrast to usual microwave split-ring resonator metasurfaces reported in literature, the present study shows both the realization by a top-down process and modelling performed in the infrared frequency range.

Modeling of the interband transitions in the optical conductivity of doped two-dimensional materials in the terahertz to the infrared frequency range: the case studies of graphene and phosphorene

We use Kramers-Kronig analysis and ab initio calculations to develop a simple analytical method for including the effects of high-energy interband electron transitions in the density polarization function of doped graphene and doped phosphorene in the optical limit. The resulting formulas are suitable for applications in the terahertz to the mid-infrared range of frequencies, where the interband electron transitions are shown to give rise to static screening with a suitably chosen in-plane polarizability. In the case of phosphorene, each component of its static polarizability tensor can be computed from a sum-rule–like formula using the ab initio data for the real part of the corresponding component of the full optical interband conductivity tensor of that material.

MATHEMATICAL MODELING AND EXPERIMENTAL STUDY OF THE PROCESS OF ELECTROMAGNETIC-CONVECTIVE DRYING OF PLANT MATERIALS

The work on electromagnetic drying with heat supply to the dried material using high and ultrahigh frequency currents and in the infrared frequency range - with oscillating energy supply is analyzed. (Research purpose) The research purpose is in analytical mathematical describing the oscillating electromagnetic-convective drying of materials, as well as the method of drying seeds of vegetable crops, non-traditional and rare plants that improve their sowing qualities. (Materials and methods) Obtained solutions to the problems of heating the material using the analytical method of integral transformations. Experimental studies were carried out on oscillating infrared drying on seeds of vegetable crops, non-traditional and rare plants. (Results and discussion) The combined electromagnetic-convective drying of materials was considered, in which the energy for drying is supplied using an electromagnetic field and convectively using a preheated drying agent. Mathematical models describing the digitizing heating of bodies of different shapes (unlimited plate, infinite cylinder, ball) under conditions of convective drying were analyzed. The results of numerical modeling of the process of oscillating infrared drying of onion seeds in a fluidized bed are presented, which show that the necessary technological drying mode can be found by numerical modeling based on the obtained models. (Conclusions) Presented mathematical models that allow numerical modeling of electromagnetic-convective drying and finding the required hardware and technological design of the process. It was determined that oscillating infrared drying of seeds of vegetable crops, non-traditional and rare plants when the seed temperature fluctuates from tmin = 34 degrees Celsius to tmax = 40 degrees Celsius causes seed stimulation, which manifests itself in an increase in germination energy and germination. It was found that the germination of vegetable seeds increases by 11-24 percent (from control), and the germination energy - by 12-73 percent, seeds of non-traditional and rare plants, respectively, by 13-24 percent and 14-82 percent.

Performance analysis of the salinity based on hexagonal two-dimensional photonic crystal: computational study

We have designed a unique structure for a liquid sensor based on two-dimensional PCs with a triangular lattice constant in the periodicity by drilling a hexagonal cylinder in a dielectric host material. Using the COMSOL multiphysics approach, we investigated the given structure and sensing performance based on the finite element method. We will optimize two-dimensional hexagonal photonic crystals to localize the photonic band gap region in the mid and far infra-red frequency range, as water is a good absorber for this range of frequencies. Then, we inject the central hexagonal cylinder with saline water and calculate the sensor parameters for different values of the refractive index of saline water at different frequencies related to photonic band gaps. We could reach the optimum conditions of the salinity sensor as the half diagonal of the hexagonal shape (R) = 500 nm, the perpendicular distance between the two diagonal hexagonal (D) = 250 nm, and the number of periods (N) = 5, which gives a high efficiency with sensitivity (S) = 525 nm/RIU, figure of merit (FOM) = 80.7 RIU−1, and quality factor (Q) = 375. The effects of structural characteristics on sensing performance are investigated, with new approaches for improving salinity sensors proposed. Furthermore, traditional salinity sensors may be replaced by the proposed method in the photo-sensing application, which is simple and practical for use in the thermal desalination techniques.

Effect of rare-earth doping on the structural and optical properties of the Ag3AsS3 crystals

Non-linear optical (NLO) materials allow the production of the coherent laser beam in the difficult frequency ranges of the electromagnetic spectrum. Aiming to explore new classes of the NLO materials with high optical performance in the infrared region, in this work, we investigated the effect of the rare earth doping (Pr, Eu, Yb) on the crystal structure and optical properties of the Ag3AsS3 crystals. The performed analysis of the XRD patterns indicates that the rare earth elements are located in the Ag sites of the crystal lattice. As a result, the second harmonic generation intensity, which determines the effectiveness of the NLO materials, increases with the increase of rare earth dopant content up to 1.0%. Using the absorption analysis and Raman spectroscopy, we show that the increase in the SHG intensity can be related to the slight decrease of the bandgap, as well as with the increased electron–phonon interaction in rare-earth-doped Ag3AsS3 crystals. Considering the discovered enhancement of the SHG intensity, accompanied by the low melting temperature, this work offers rare-earth-doped Ag3AsS3 crystals as potential candidates for the non-linear optical applications for the infrared frequency range.

Extending plasmonic response to the mid-wave infrared with all-epitaxial composites.

Highly doped semiconductor "designer metals" have been shown to serve as high-quality plasmonic materials across much of the long-wavelength portion of the mid-infrared. These plasmonic materials benefit from a technologically mature semiconductor fabrication infrastructure and the potential for monolithic integration with electronic and photonic devices. However, accessing the short-wavelength side of the mid-infrared is a challenge for these designer metals. In this work we study the perspectives for extending the plasmonic response of doped semiconductors to shorter wavelengths by leveraging charge confinement, in addition to doping. We demonstrate, theoretically and experimentally, negative permittivity across the technologically vital mid-wave infrared (3-5 μm) frequency range. The semiconductor composites presented in our work offer an ideal material platform for monolithic integration with a variety of semiconductor optoelectronic devices operating in the mid-wave infrared.

Numerical investigation of the tunable polarizer using gold array and graphene metamaterial structure for an infrared frequency range

Numerical investigation of the tunable polarizer using gold array and graphene metamaterial structure for an infrared frequency range

Optical Scattering Characteristics of 3-D Lunar Regolith Particles Measured Using X-Ray Nano Computed Tomography

Shape, in addition to size and material composition, has a strong effect on the optical scattering characteristics of a particle. In this work, we computationally study how the measured 3-D shapes of individual lunar regolith particles affect their optical scattering characteristics. The shapes of 25 lunar regolith particles collected during the Apollo 11 mission were measured using X-ray nano computed tomography (XCT). The scattering cross sections (CSs) of particles that ranged in size between 400 and 1000 nm were computed using the Discrete Dipole Scattering (DDSCAT) software in the visible to the infrared frequency range. The orientation-averaged scattering CS of the lunar regolith particles was then compared with that of spheres of the same volume. The comparison shows that the shape of lunar regolith particles decreases the resonance wavelength by 20%, on average, compared with the spheres of the same volume. On the other hand, the peak scattering CS is found to be nearly independent of shape for the suite of particles studied. Also, lunar regoliths are found to generate a slightly lower single scattering albedo and have a higher phase function asymmetry parameter in comparison to spherical particles of the same volume. These differences highlight the importance of accounting for 3-D shape variations in understanding the optical response of lunar regolith particles.

Graphene-Based Tunable Broadband Polarizer for Infrared Frequency

This paper proposes the tunable graphene-assisted polarizer structure which is working on the infrared frequency range. The tunable polarizer has been designed by a three-layered structure of silica, graphene, and gold. The polarizer behavior of the structure is analyzed for the frequency range of 3 to 12 THz. The tunability of the structure is analyzed for the different values of Fermi energy which is a tunable parameter of the single-layer graphene sheet. Polarizer response is derived in terms of different performance parameters such as reflectance, phase variation, phase difference, polarization conversion rate, and effective refractive indices. Graphene-based polarizer structure is investigated for the co-polarization and cross-polarization input incident conditions to check linear to circular polarization conversion. It also shows an effective refractive index response to check the metasurface behavior of the polarizer for the 3 to 12 THz range. We have observed that the polarization amplitude becomes stronger for the higher Fermi energy value of the graphene sheet. The reflection amplitude is achieved up to 90%. Results of the proposed polarizer structure can be used to design the various electro-optical structure which operates in the lower terahertz range.

Experimental demonstration of ghost imaging with speckled light in long-wavelength infrared range

Infrared imaging with a single-pixel camera can achieve radiometric accuracy not currently available with multi-pixel thermal cameras. One of the actively investigated single-pixel camera technology is ghost imaging. We propose an optical design to experimentally demonstrate classical ghost imaging in the long-wave infrared frequency range with speckled light without using a spatial light modulator. We obtained an example low-quality ghost image and then used the cross-correlation function to identify and explain the main difficulties in ghost imaging with a thermal camera.

Vibrational Spectroscopy of Benzonitrile-(Water)1-2 Clusters in Helium Droplets.

Polycyclic aromatic hydrocarbons are considered as primary carriers of the unidentified interstellar bands. The recent discovery of the first interstellar aromatic molecule, benzonitrile (C6H5CN), suggests a repository of aromatic hydrocarbons in the outer earth environment. Herein, we report an infrared (IR) study of benzonitrile-(D2O)n clusters using mass-selective detection in helium nanodroplets. In this work, we use isotopically substituted water, D2O, instead of H2O because of our restricted IR frequency range (2565-3100 cm-1). A comparison of the experimental and predicted spectra computed at the MP2/6-311++G(d,p) level of benzonitrile-(water)1-2 clusters reveals the formation of a unique local minimum structure, which was not detected in previous gas-phase molecular beam experiments. Here, the solvent water forms a nearly linear hydrogen bond (H-bond) with the nitrile nitrogen of benzonitrile, while the previously reported most stable cyclic H-bonded isomer is not observed. This can be rationalized by the stepwise aggregation process of precooled monomers. The addition of a second water molecule results in the formation of two different isomers. In one of the observed isomers, a H-bonded water chain binds linearly to the nitrile nitrogen similar to the monohydrated benzonitrile-water complex. In the other observed isomer, the water dimer forms a ring-type structure, where a H-bonded water dimer simultaneously interacts with the nitrile nitrogen and the adjacent ortho CH group. Finally, we compare the water-binding motif in the neutral benzonitrile-water complex with the corresponding positively and negatively charged benzonitrile-water monohydrates to comprehend the charge-induced alteration of the solvent binding motif.

Effect of sample anisotropy on scanning near-field optical microscope images

Scattering-type scanning near-field optical microscopy (s-SNOM) has been widely used to characterize strongly correlated electronic, two dimensional, and plasmonic materials, and it has enormous potential for biological applications. Many of these materials exhibit anisotropic responses that complicate the extraction of dielectric constants from s-SNOM measurements. Here, we generalize our recently developed approach for retrieving the near-field scattering signal from isotropic systems and apply it to anisotropic dielectrics. Specifically, we compare our theoretical results with experimental measurements on modestly anisotropic sapphire that exhibit strong resonances at the infrared frequency range. Good agreement with the experimental result is found. Our result is important for understanding the near-field response of low damping, anisotropic polaritonic states in dielectric media.

Electrical control of anisotropic and tightly bound excitons in bilayer phosphorene

Monolayer and few-layer phosphorene are anisotropic quasi-two-dimensional (quasi-2D) van der Waals (vdW) semiconductors with the linear-dichroic light-matter interaction and the widely tunable direct band gap in the infrared frequency range. Despite recent theoretical predictions of strongly bound excitons with unique properties, it remains experimentally challenging to probe excitonic quasiparticles due to the severe oxidation that occurs during device fabrication. In this study, we report the observation of strongly bound excitons and trions with highly anisotropic optical properties in intrinsic bilayer phosphorene, which are protected from oxidation by encapsulation with hexagonal boron nitride (hBN) in a field-effect transistor (FET) geometry. Reflection contrast and photoluminescence spectroscopy clearly reveal the linear-dichroic optical spectra from anisotropic excitons and trions in the hBN-encapsulated bilayer phosphorene. The optical resonances from the exciton Rydberg series indicate that the neutral exciton binding energy is over 100 meV even with the dielectric screening from hBN. The electrostatic injection of free holes enables an additional optical resonance from a positive trion (charged exciton) \ensuremath{\sim}30 meV below the optical band gap of the charge-neutral system. Our work shows exciting possibilities for monolayer and few-layer phosphorene as a platform to explore many-body physics and photonics and optoelectronics based on strongly bound excitons with twofold anisotropy.

MODELING AND CALCULATION OF THE PHOTOLUMINESCENCE SPECTRUM OF A HETEROSTRUCTURE WITH A QUANTUM WELL BY THE EXAMPLE OF ALGaAS / GaAS

This research aims to improve the available means for characterizing the emission properties of quantum well heterostructures by modeling and calculating the absorption and photoluminescence spectra using the GaAs/AlGaAs heterostructure as an example. Research is conducted based on multilayer heterostructures and heterostructures with quantum wells to develop detectors and emitting elements in the infrared frequency range, pulsed solid-state generators in the millimeter and submillimeter-wave ranges. The study of radiating properties of heterostructures with a quantum well on A3B5 compounds has become widespread [1-3]. It is possible to control the heterostructure's emission frequency by selecting the optimal composition of the wideband semiconductor layer, the level and type of its doping, the doping region, and the quantum well layer width, which is of applied importance for the development of optoelectronic devices. Technologies for manufacturing such heterostructures are labor-intensive, time-consuming, and expensive processes, which contribute to developing methods for modeling and calculating the characteristic frequencies of radiation and absorption of radiation. Based on such calculations, radiating elements of the submicronic wavelength range can be developed based on heterostructures with a quantum well on the A3B5 type compounds. [4]

МОДЕЛИРОВАНИЕ И РАСЧЕТ СПЕКТРА ФОТОЛЮМИНЕСЦЕНЦИИ ГЕТЕРОСТРУКТУРЫ С КВАНТОВОЙ ЯМОЙ НА ПРИМЕРЕ ALGaAS/GaAS

This research aims to improve the available means for characterizing the emission properties of quantum well heterostructures by modeling and calculating the absorption and photoluminescence spectra using the GaAs/AlGaAs heterostructure as an example. Research is conducted based on multilayer heterostructures and heterostructures with quantum wells to develop detectors and emitting elements in the infrared frequency range, pulsed solid-state generators in the millimeter and submillimeter-wave ranges. The study of radiating properties of heterostructures with a quantum well on A3B5 compounds has become widespread [1-3]. It is possible to control the heterostructure's emission frequency by selecting the optimal composition of the wideband semiconductor layer, the level and type of its doping, the doping region, and the quantum well layer width, which is of applied importance for the development of optoelectronic devices. Technologies for manufacturing such heterostructures are labor-intensive, time-consuming, and expensive processes, which contribute to developing methods for modeling and calculating the characteristic frequencies of radiation and absorption of radiation. Based on such calculations, radiating elements of the submicronic wavelength range can be developed based on heterostructures with a quantum well on the A3B5 type compounds. [4]

Graphene based photonic crystals including anisotropic defect layers with highly tunable optical responses in infrared frequency range

Abstract‒ Optical features of three one dimensional photonic crystals are studied theoretically. First structure which consists of SiO2 slabs separated by graphene sheets is considered as an ideal crystal with tunable response. Adding anisotropic liquid crystal (LC) layers inside the ideal structure, two defective crystals are also proposed to assess their potential of being used in photonics. Dependence of the crystals transmittance to periods of the layers as well as size of the SiO2 and LC slabs are studied at first. Extracting the optimum values for these structural parameters, tunability of the optical response of the proposed crystals by using externally controllable parameters such as: optical axis of the anisotropic layer, light incident angle, crystal temperature and graphene layer chemical potential are evaluated systematically. Results clearly reflect that all suggested crystals might be useful to support the increasing demands of optical integrated circuit technology for adjustable photonic elements.

Optical dielectric constants of single crystalline silver films in the long wavelength range

Optical dielectric constants are critical to modeling the electronic and optical properties of materials. Silver, as a noble metal with low loss, has been extensively investigated. The recently developed epitaxial growths of single crystalline Ag on dielectric substrates have prompted efforts to characterize their intrinsic optical dielectric function. In this paper, we report spectral ellipsometry measurements and analysis of a thick, epitaxially-grown, single-crystalline Ag film. We focus on the range of 0.18 – 1.0 eV or 1.24 – 7 µm, an energy and wavelength range that has not been examined previously using epitaxial films. We compare the extracted dielectric constants and the predicted optical performances with previous measurements. The loss is appreciably lower than the widely quoted Palik’s optical constants (i.e., up to a factor of 2) in the infrared frequency range. The improved knowledge of fundamental optical properties of the high-quality epitaxial Ag film will have a broad impact on simulations and practical applications based on Ag in the long wavelength range.