Refractive Index Spectra Research Articles

Terahertz characterization of organic crystals using paraffin as dilution matrix

Terahertz waves exhibit excellent performance in molecular information detection of substances. Since natural materials exhibit weak absorption of terahertz waves, it's conventional to involve mixing analyte with polymer diluents and pressing them into pellets, or enhance the light-material interaction through coupling systems of natural materials with metamaterials. However, both pressure-induced metastable crystal structure transformations and spatial overlap between the analyte and metasurfaces can impact the absorption of terahertz waves by organic crystals. This paper proposes a novel analytical approach using paraffin as a dilution matrix for qualitatively and quantitatively characterizing organic crystals with THz spectroscopy. The featureless refractive index spectra and negligible absorption demonstrated the feasibility of paraffin as a diluting analyte. The analytical process was further demonstrated with well-studied lactose by being diluted in molten paraffin at different mass-ratios and solidified as pellets under room temperature and ambient pressure. A continuous wave terahertz frequency domain spectroscopy system (THz-FDS) is used for spectral acquisition over 0.4–1.3 THz. The experimental results reveal a significant linear correlation between the absorption coefficient peak areas and molar concentration of lactose, with a correlation coefficient R2 of 0.9678. Our method provides an additional optional dilution matrix for terahertz spectroscopy characterization of organic crystals, enabling non-destructive, rapid, and direct measurement of metastable crystals. Furthermore, this study on paraffin as a binder material holds potential for enhancing spatial overlap between natural materials and metamaterials in the field of metasurface-enhanced sensing.

Separating Surface Reflectance from Volume Reflectance in Medical Hyperspectral Imaging.

Hyperspectral imaging has shown great promise for diagnostic applications, particularly in cancer surgery. However, non-bulk tissue-related spectral variations complicate the data analysis. Common techniques, such as standard normal variate normalization, often lead to a loss of amplitude and scattering information. This study investigates a novel approach to address these spectral variations in hyperspectral images of optical phantoms and excised human breast tissue. Our method separates surface and volume reflectance, hypothesizing that spectral variability arises from significant variations in surface reflectance across pixels. An illumination setup was developed to measure samples with a hyperspectral camera from different axial positions but with identical zenith angles. This configuration, combined with a novel data analysis approach, allows for the estimation and separation of surface reflectance for each direction and volume reflectance across all directions. Validated with optical phantoms, our method achieved an 83% reduction in spectral variability. Its functionality was further demonstrated in excised human breast tissue. Our method effectively addresses variations caused by surface reflectance or glare while conserving surface reflectance information, which may enhance sample analysis and evaluation. It benefits samples with unknown refractive index spectra and can be easily adapted and applied across a wide range of fields where hyperspectral imaging is used.

(Invited) High Temperature Exciton Properties in Aggregated Single-Walled Carbon Nanotubes

Individual single-walled carbon nanotubes (SWCNTs) at high temperatures have been reported to generate narrow-band thermal radiation in the near-infrared region due to thermally robust excitonic effects [1,2]. This phenomenon potentially offers a new opportunity for utilizing exciton properties in thermal engineering such as thermophotovoltaic energy harvesting requiring excellent wavelength selective near-infrared thermal emitter. However, for its realistic applications in macroscale, it is necessary to make the distinct exciton effect available under high temperature conditions in macroscopic assemblies of SWCNTs. As a first step toward this goal, we have recently determined broadband complex refractive index spectra of single-chirality SWCNT membranes in which SWCNTs are aligned two-dimensionally in a plane [3] and reported their birefringent properties [4]. In the presentation, we will discuss the change in the optical spectra of SWCNT assemblies with increasing temperature, as well as how the aggregation states affect the exciton properties. [1] T. Nishihara, A. Takakura, Y. Miyauchi, and K. Itami, Nat. Commun. 9, 3144 (2018). [2] S. Konabe, T. Nishihara, and Y. Miyauchi, Opt. Lett. 46, 3021 (2021). [3] T. Nishihara, A. Takakura, M. Shimasaki, K. Matsuda, T. Tanaka, H. Kataura, and Y. Miyauchi, Nanophotonics 11, 1011 (2022). [4] H. Wu, T. Nishihara, A. Takakura, K. Matsuda, T. Tanaka, H. Kataura, and Y. Miyauchi, Carbon, in press.

Mid-Infrared Dispersion Spectroscopy as a Tool for Monitoring Time-Resolved Chemical Reactions on the Examples of Enzyme Kinetics and Mutarotation of Sugars.

Ongoing technological advancements in the field of mid-infrared (MIR) spectroscopy continuously yield novel sensing modalities, offering capabilities beyond traditional techniques like Fourier transform infrared spectroscopy (FT-IR). One such advancement is MIR dispersion spectroscopy, utilizing a tunable quantum cascade laser and Mach-Zehnder interferometer for liquid-phase analysis. Our study assesses the performance of a custom MIR dispersion spectrometer at its current development stage, benchmarks its performance against FT-IR, and validates its potential for time-resolved chemical reaction monitoring. Unlike conventional methods of IR spectroscopy measuring molecular absorptions using intensity attenuation, our method detects refractive index changes (phase shifts) down to a level of 6.1 × 10-7 refractive index units (RIU). This results in 1.5 times better sensitivity with a sevenfold increase in analytical path length, yielding heightened robustness for the analysis of liquids compared to FT-IR. As a case study, we monitor the catalytic activity of invertase with sucrose, observing the formation of resultant monosaccharides and their progression toward thermodynamic equilibrium. Anomalous refractive index spectra of reaction mixtures, with substrate concentrations ranging from 2.5 to 25 g/L, are recorded, and analyzed at various temperatures, yielding Michaelis-Menten kinetics findings comparable to the literature. Additionally, the first-time application of two-dimensional correlation spectroscopy on the recorded dynamic dispersion spectra correctly identifies the mutarotation of reaction products (glucose and fructose). The results demonstrate high precision and sensitivity in investigating complex time-dependent chemical reactions via broadband refractive index changes.

Polymer-like hydrogenated amorphous carbon thin films fabricated by plasma-enhanced chemical vapor deposition of cyclohexane precursor

Hydrogenated amorphous carbon (a-C:H) films were fabricated by plasma-enhanced chemical vapor deposition (PECVD) of a cyclohexane precursor at ambient temperature at varying deposition pressures from 19.73 to 38.00 Pa and varying plasma powers from 20 to 80 W. The deposition rate of the a-C:H films was strongly dependent on the deposition conditions. The films were all optically transparent with extinction coefficient below 0.0042. The refractive index as an indicator of the film's density varied depending on the deposition conditions. Their surfaces were all hydrophobic regardless of the deposition conditions. The a-C:H films had wide optical bandgaps ranging from 3.09 to 3.69 eV. The refractive index and FTIR spectra were consistent with those of polymer-like a-C:H films. As the deposition pressure decreased and plasma power increased, the intensity of a dominant peak of CHx stretching mode in the FTIR spectra decreased. The relative hydrogen content of the a-C:H films was estimated from an FTIR analysis and determined to have an inverse relationship with refractive index. These results indicated that the formation of more energetic plasmas during deposition at lower pressures and higher plasma powers led to the a-C:H films with reduced hydrogen content and increased density. The observed film properties could be advantageous for several applications, particularly as protective, wear-resistant, low-friction, or anti-reflective coatings for optical windows.

Renormalizing the high-harmonic interference via double-slit and grating

A method to utilize high-harmonic interference in Young’s double-slit followed by a grating holds promise for precisely measuring the refractive-index spectrum in the extreme ultraviolet (EUV) region. The measurement is currently bottlenecked by the time it takes to fit the Fresnel interference patterns. The conventional fitting procedure, involving multiple numerical integrals for evaluating the EUV propagation through the slit and grating, takes ≳30min on a standard laptop computer, while the data acquisition time is ∼200s. Here, we apply an analytic Gaussian integral and bypass one of the numerical integrals associated with the grating. The analysis reduces to evaluating a renormalized EUV propagation in a simple double-slit interferometer, and the estimated fitting time on a laptop becomes as short as 112 s. Our study enables real-time analysis during measurements, facilitating mass optical-data collection of EUV lithography materials.

Pressure effects on the structural, electronic, elastic, optical, and vibrational properties of YMg intermetallic compounds: a first-principles study

The properties of YMg in B2 structure have been comprehensively analysed using the first-principles plane-wave pseudopotential method. Specifically, the structural, electronic, elastic, vibrational, and optical properties were investigated using the generalized gradient approximation (GGA) method in the context of density functional theory. The Vienna ab initio simulation package (VASP) was utilized for these calculations. The computed lattice parameter (3.803 Å) and bulk modulus (41.33 GPa) are consistent with the earlier data on ambient pressure. The electronic band structure and energy-dependent density of states reveal the metallic nature of the titled compounds. The Born stability requirements confirmed the mechanical stability. The analysis of Pugh’s and Poisson’s ratios and Cauchy’s pressure reveals that YMg is ductile under the pressures in consideration. According to several anisotropy indices, the compound is noticeably anisotropic both in ambient and under pressure. Our investigation includes an analysis of several fundamental mechanical parameters of the material, including the bulk modulus, the pressure derivative of the Zener anisotropy factor, Poisson’s ratio, isotropic shear modulus and Young’s modulus with a particular focus on their dependence on pressure. We have determined that the elastic constants obtained remain mechanically stable, satisfying the Born Stability conditions even at high pressures of up to 60 GPa. To explore the dynamic stability of YMg, we analysed the material’s phonon dispersion curves. The examined compound displays stability under dynamic conditions from 0 GPa to 30 GPa, as evidenced by its positive vibration frequencies. However, this stability is not sustained under higher pressure, as the compound becomes unstable after 30 GPa to 70 GPa. The electronic band structure and density of states diagrams demonstrate YMg’s metallic properties. At atmospheric pressure (0 GPa), the total density of states (TDOS) near the Fermi level is approximately 1.63 states/eV, with pressure application reducing DOS. The dielectric function, refractive index, and energy loss spectra are examined within the 0–20 eV energy range. YMg exhibits its highest absorption between 4 and 11 eV. The peak optical conductivity is observed around 0.78 eV (equivalent to 1589.5409 nm), while the most significant energy loss occurs at 11.90 eV, roughly corresponding to 2.8 Hz in the ultraviolet spectrum. Moreover, we extensively analyzed the material’s phonon thermodynamic and optical properties, providing insights into its behavior under various conditions. The outcomes acquired at zero pressure are generally coherent with the current theoretical values.

Growth, thermal, spectroscopy and ∼2.7 μm multiwavelength laser output of Er:GYAP crystal

We demonstrate the growth, thermal, spectroscopy and laser performance of a Er3+ doped Gd0.1Y0.9AlO3 (Er:GYAP) disorder crystal grown by Czochralski method. The crystal with space group Pbnm and lattice parameters of =0.5185 nm, =0.5327 nm, =0.7378 nm, α=β=γ=90° and =0.203784 nm3 are obtained by fitting powder X-ray diffraction data. The Mohr’s hardnesses along three axes are 6.94, 7.27, and 7.44. The thermal expansion coefficient of axis is 4.20 × 10–6 K–1 and the density is 5.88 g/cm3. The thermal conductivities are characterized as =6.24, =5.57, and =6.83 W/(m·K). Meanwhile, the refractive index, absorption and emission spectra in triaxial directions are determined. Besides, level lifetimes of 4I11/2 and 4I13/2 are 0.86 and 2.83 ms. Finally, the ∼2.7 μm multiwavelength laser outputs are observed with maximum average power of 628 mW and beam quality factors / of 1.42/1.45. The results prove that the Er:GYAP crystal is a promising gain medium for generating mid-infrared lasers.

Research on classification methods for rubber based on terahertz time-domain spectroscopy with data fusion strategy

Rubber, an essential industrial product, plays a crucial role in industry and human life. However, some manufacturers of rubber use inferior, recycled or low-cost rubber materials to replace high-quality rubber products. Therefore, in order to ensure industrial production, protect natural environment and ensure personal safety, it is of great economic and social significance to enable rapid and non-destructive qualitative identification of rubber products. In this paper, eight different types of black rubber, including Nitrile Butadiene Rubber (NBR), Choloroprene Rubber (CR) and Ethylen Propylen Diene Monomer (EPDM), were selected as research objects. Terahertz Time-Domain Spectroscopy (THz-TDS) technology was utilized to get the absorption spectra, refractive index spectra and time-domain spectra of these samples for exploring the differences between different types of rubber in terahertz spectra. To reduce the data volume, three band selection algorithms were employed to extract features from the absorption spectra and refractive index spectra, and temporal features of time-domain spectra were extracted for subsequent data processing. In the selection of classification model algorithms, K-Nearest Neighbor (KNN), Random Forest (RF) and Supervised Kohonen Neural Networks (S-Kohonen) were employed to recognize these spectral data. To fully exploit the latent information within these data and considering the possibility of the loss of partial information in single-type signal, a feature-level data fusion method was applied to different optical parameter signals to obtain more information about terahertz spectra during the process of data modeling. The results of the research indicated that the model with the highest prediction accuracy was the KNN model, with an accuracy of 97.37%, when refractive index spectra and time-domain spectra were fused as inputs, the F1-score reached 99.64. The performance of data fusion was noticeably better than that of a single-type signal. This study validates the feasibility of using terahertz time-domain spectroscopy for qualitative identification of different types of rubber.

Behavior of fullerene C60 in xylene-dimethylformamide binary solvents

The formation of colloidal species of fullerene C60 in two component (xylenedimethylformamide) organic solvents was studied for the first time. The results of the study of the refractive index and UV-visible spectra of C60 solutions were accompanied by an analysis of the particle size using the dynamic light scattering (DLS) method. A correlation has been established between the change in the refractive index of the solution and the degree of selforganization of fullerene molecules in solution at different concentrations and storage periods. It is shown that in the xylene-dimethylformamide binary system, the absorption spectra of C60 (~0.22 mg/ml) do not retain spectral features in a pure solvents when the solution is stored after 5 days. It has been established that, over time, the C60-xylene-dimethylformamide solution becomes polydisperse, and the sizes of the resulting fullerene nanoaggregates depend on the initial C60 concentration.

Oxidative desulfurization of fuels using alcohol-based DESs.

The presence of sulfur-containing compounds in fuel oil has become a major global issue due to their release of toxic sulfur dioxide. Hydrodesulfurization is a commonly used method for removing sulfur from fuel. However, new desulfurization techniques have been developed recently as hydrodesulfurization (HDS) is ineffective in removing refractory sulfur, e.g., BT, DBT, 4-MDBT. In this study, a series of deep eutectic solvent (DES) using ChCl, salicylic acid, oxalic acid, citric acid, and adipic acid as hydrogen bond acceptors and MeOH, EtOH, BuOH, EG, DEG, and TEG as hydrogen bond donors on different mole ratios were synthesized and then investigated the efficiency of these DESs in extracting sulfur from model and diesel fuel. Densities, viscosity, refractive index, and FTIR spectra of synthesized DESs were recorded. It also included oxidative desulfurization, which is a promising approach offering high selectivity, mild reaction conditions, low cost, and high efficiency. Hydrogen peroxide was selected as the oxidant in this study due to its excellent performance, commercial availability, and high proportion of active oxygen. [Citric acid: TEG] [1:7] and [adipic acid: TEG] [1:8] were found to be the most effective, removing up to 44.07% and 42.53% sulfur from model oil during single-stage extraction at 30°C using a solvent-to-feed ratio of 1.0 and was increased to 86.87% and 85.06% using successive extraction up to the fourth stage. On oxidation, extraction efficiencies were reported to be 98.98%, 87.79%, and 56.25% and 96.96%, 81.22%, and 44.51% for model oil containing DBT and diesel 1 and diesel 2 with DES [citric acid: TEG] [1:7] and [adipic acid: TEG] [1:8] respectively at 30°C using a solvent-to-feed ratio of 1.0. The study found that [citric acid: TEG] [1:7] exhibits better extraction performance in the deep desulfurization of fuels at an extraction temperature of 30°C.

Physical and Optical Properties of CeF<sub>3</sub> Doped with Aluminium Fluorophosphate Glasses

Glass doped with cerium is an attractive material for a variety of applications. The aluminium fluorophosphate glasses were made by the conventional melt-quenching technique. The glass samples were characterized by density, refractive index, FTIR and photoluminescence spectra. The density was shown to increase, but refractive and molar volume were shown to decrease. The FTIR spectra of these glasses showed mainly [PO3] and [PO4] structural units. Transparency of the glass samples is demonstrated by a transmission intensity in the 70-80% range. Regarding the optical properties, under 307 nm excitation, the emission peak around 348 nm of the CeF3-doped aluminium fluorophosphate glasses was confirmed. The emission would be due to the 5d→4f transitions of Ce3+ ions.

Optical properties and electric modulus studies of TSP: CH3COONa based biopolymer electrolytes

The research of biopolymers for the creation of solid polymer electrolytes (SPE) for electrochemical devices has resulted from the green revolution. Various strategies have been used to build and characterise biopolymer-based membranes for proton and lithium-ion conduction. However, research on biopolymers based on sodium ions is uncommon in the literature. The solution cast approach is used in this work to create a SPE based on the biopolymer Tamarind Seed Polysaccharide (TSP) incorporated with sodium acetate (CH3COONa). UV–visible optical absorption spectroscopy in the wavelength range of 200–800 nm was used to investigate the optical characteristics. From the studies of optical absorption, optical transmission, optical absorption coefficient, refractive index spectrum, extinction coefficient spectra, direct energy bandgap, indirect energy bandgap, optical absorption edge, Urbach – energy, and optical dielectric loss were calculated. The comparative study of the optical dielectric loss to the optical bandgap showed that the direct allowed transition was the most probable electronic transition for the prepared films. The calculated optical bandgap (Direct allowed) was decreased for 80:20 film from 5.51 eV (for pure TSP) to 4.88 eV. The direct, indirect, and absorption edges for pure TSP were all high, and when the salt concentration of CH3COONa increased, the above characteristics progressively decreased. For 80 % TSP: 20 % CH3COONa concentration, a low direct and indirect energy bandgap value was obtained. Tangent loss and electric modulus experiment results were then presented using AC Impedance data. For the 80:20 film, the tangent energy loss revealed a minimum and the electric modulus spectra exhibited the zeroth tail is at its maximum.

A generalized and comprehensive slant channel modeling method for underwater wireless optical communication and its system performance analysis

The underwater wireless slant optical link is a more generalized type of communication links compared with vertical and horizontal links. Since several oceanic factors including temperature and salinity variations with the seawater depth, the performance of the slant link for the underwater wireless optical communication (UWOC) will be overestimated under the assumptions of constant temperature and salinity. To this end, this paper proposes a model of slant link considering the depth-dependent and inclination-angle-dependent turbulence and scattering that are the main causes of multipath fading for UWOC. Specifically, to model the turbulence-induced fluctuations of light fields, the random phase screen method is exploited, where the power spectrum of refractive index is calculated using the oceanic turbulence optical power spectrum (OTOPS) model and the light fields at the receivers are derived by the angular spectrum method. To emulate the scattering-induced divergence, the scattering phase function is applied, where the motion directions and coordinates of light spots propagating among phase screens are deduced using Rodrigues’ Rotation Formula. Simulation results demonstrate the effects of the depths and inclination angles of transmitters on the performance of UWOC by analyzing the scintillation index, channel impulse response, and BER (bit error rate).

Optical, photo-physical and photo-stability characterizations of malachite green as a laser dye, combined with TD-DFT simulations

The optical properties of Malachite green (Mg) dye were examined experimentally, including absorption, optical energy gab, refractive index, dielectric constant, optical conductivity and emission spectra in various solvents. Additionally, several significant photophysical parameters were evaluated, including the extinction coefficient (ε), the energy yield of fluorescence (Ef), the length of attenuation Λ (λ), oscillator strength (f), quantum yield (Øf), fluorescence lifetime ({uptau }_{{text{f}}}), decay rate radiative constant (kr), and the dipole moment (μ) in addition to absorption and emission cross-sections (σa) and (σe) respectively. Time Dependent Density function theory (TD-DFT) computations were used to generate the theoretical absorption spectra of the (Mg) compound. The energy gap (Eg), electron density, and electrostatic potential were also simulated.

A first-principles investigation on the structural, electronic and optical characteristics of tetragonal compounds XAgO (X = Li, Na, K, Rb)

First-principles calculations employing the density functional theory full-potential (linearized) augmented plane-wave plus local orbitals (FP-(L)/APW + lo) method were conducted to investigate the structural, electronic and optical characteristics of silver-based ternary oxides XAgO (X = Li, Na, K, and Rb). The GGA-PBEsol and TB-mBJ functionals were employed to describe the exchange-correlation potential. The optimized lattice parameters and atomic positions obtained from the calculations exhibit good agreement with both theoretical predictions and experimental measurements. Various exchange-correlation functionals were employed to evaluate the electronic properties, revealing that the newly developed Tran–Blaha modified Becke–Johnson functional yields a significant improvement in the band gap value. All XAgO compounds under consideration are categorized as semiconductor materials where the band gap value decreases as the atomic size of the X element increases. The study also explored the total and site-projected l-decomposed densities of states. Additionally, the complex dielectric function, refractive index, extinction coefficient, reflectivity, and loss function spectra were calculated for the incident radiation polarized parallel to both the [100] and [001] crystalline directions. The interband transitions that contribute effectively to the observed peaks in the imaginary part of the dielectric function were identified.

High resolution terahertz ATR frequency-domain spectroscopy for monitoring spinal cord injury in rats.

Traumatic spinal cord injury (SCI) can lead to permanent neurological impairment, underscoring the urgency of regular therapeutic intervention and monitoring. In this study, we propose a new strategy for monitoring spinal cord injury through serum based on high-resolution THz attenuated total reflection frequency domain spectroscopy (THz-ATR-FDS). We demonstrated serum spectral differences at different time points after experimental SCI in rats. We also studied the relationship between serum lipid concentration and the time of SCI, which revealed the potential of lipid molecules as biomarkers of SCI. In addition, based on the principal component analysis (PCA) and least squares regression (LSR) models, the quantitative relationship between the refractive index spectrum and lipid concentration in serum was automatically analyzed. This work highlights terahertz spectroscopy as a promising tool for label-free, periodic, and efficient monitoring of SCI.

Birefringent optical responses of single-chirality carbon nanotube membranes

Membranes composed of single-walled carbon nanotubes (SWCNTs) with a specific chiral structure (chirality) possess unique optical properties dominated by thermally robust quasi-one-dimensional excitons. Therefore they have emerged as promising materials for photonic and/or thermo-optic applications. As SWCNTs in the membranes are usually aligned two-dimensionally in a plane, and the optical responses of individual SWCNTs are highly anisotropic, the macroscopic responses of membranes are expected to depend on the light-propagation direction. However, the complex refractive-index spectra of some membrane axes are unknown, hindering the optical design of SWCNT-based devices that respond to arbitrarily propagating light. Here, we report the anisotropic complex refractive index spectra of a single-chirality SWCNT membrane fabricated via vacuum filtration. The polarization- and angle-resolved reflection spectra were obtained in the near-infrared-to-visible region. All spectral features in different polarizations and incident angle configurations were consistent with a uniaxial birefringent membrane, reflecting the random in-plane orientations of the SWCNTs. The ordinary (in-plane) refractive index spectra presented a series of sharp resonances of parallel-polarized excitons. The extraordinary (out-of-plane) refractive index in the 0.8–2.4 eV range was determined as ∼1.9. The extraordinary spectra included small but indispensable contributions from the cross-polarized exciton resonance, which are necessary for properly predicting the angle-dependent optical responses of the membrane. By completely unveiling the birefringent optical responses of single-chirality SWCNT membranes, this work paves the way for integrating SWNCT membranes into precise and diverse photonic and/or thermo-optic devices.

First-principles study of ZnSn1−xTaxO3 (x=2.5% and x=5%) for opto-electronics and electronic structure properties

This study employs density functional theory (DFT) calculations to investigate the impact of tantalum (Ta) doping in ZnSnO3 to investigate the electronic and optoelectronic properties. ZnSnO3 is a promising semiconductor material with a wide bandgap and visible light transparency, making it suitable for optoelectronic applications. However, its low electrical conductivity limits its performance in these applications. The results revealed that our structural parameters are in good agreement with the experimental values. The electronic structures revealed that the top of the valence band and the bottom of the conduction band are decided by O 2p and Sn 5s states, respectively, and that ZnSn[Formula: see text]TaxO3 presented a direct band gap (1.0[Formula: see text]eV) located at [Formula: see text]-point. Finally, the complex dielectric function and optical constants (such as absorption spectrum, refractive index, extinction coefficient, reflectivity, and energy-loss spectrum) were obtained and discussed in detail. Our findings also suggested that ZnSn[Formula: see text]TaxO3 is a promising transparent semiconductor and photocatalyst. These insights provide opportunities for high-performance optoelectronic device design such as biomedical and LED.

Surface and guided waves near the interface between the media with an abruptly change in the dielectric constant and a parabolic permittivity profile

The waveguide features of the planar interface separating the different optical media with a parabolic permittivity profile and with an abrupt change in the dielectric constant with growing the electric field are studied. A new form of the dielectric permittivity consisting of a parabolic spatial distribution and an intensity-dependent nonlinear part is proposed. Exact solutions to the wave equation with proposed complicated permittivity describing the new types of surface and guided transverse electric (TE) waves are found in the case of both continuous and discrete spectrum of the effective refractive index. The influence of the optical parameters of the contacting media on the wave distribution profiles and their properties are analyzed. A growing width of graded-index layer makes it possible to enlarge the penetration depth of the surface wave existing in the discrete spectrum and to reduce it in the continuous spectrum.