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At least 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Diamagnetic susceptibility and optical properties of a spherical quantum dot: effects of the parabolic and the shifted parabolic potentials

Centred charge donor related diamagnetic susceptibility and optical properties of a spherical GaAs quantum dot are presented. In particular, effects of intrinsic parabolic and shifted parabolic potentials on these quantities are investigated. This is theoretically achieved by solving the Schrödinger equation within the effective mass approximation. It is observed that the parabolic potential reduces the magnitude of the diamagnetic susceptibility while the shifted parabolic potential increases it. Other findings are that the parabolic potential blue-shifts both the absorption coefficient and the change in refractive index of quantum dots, while the shifted parabolic potential red-shifts these quantities. These features are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Modeling and design of tin doped group IV alloy based QWEAM

This work investigates vital characteristics of tin doped group IV based quantum well for its potential as an electroabsorption modulator (EAM). Absorption coefficient and refractive index variation in proposed EAM structure are evaluated and studied under variation of electric field. Performance parameters like extinction ratio, chirp factor, etc. are calculated for different electric fields and Sn content of GeSn quantum well. A significant negative chirp and high extinction ratio has been obtained at midinfrared range of wavelength. The result reveals that appropriate selection of external field and Sn content plays a decisive role in the performance of QWEAM. Moreover, there is a tradeoff between extinction ratio and insertion loss on increasing length of the modulator.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Optoelectronic properties of germanium iodide perovskites AGeI{sub 3} (A = K, Rb and Cs): first principles investigations

In this paper, we have investigated the structural, optoelectronic and elastic properties of AGeI{sub 3} (A = K, Rb and Cs) using the density functional theory with generalized gradient approximation (GGA) for potential exchange correlation. The modified Becke–Johnson (mBJ-GGA) potential approximation is also used for calculating the optoelectronic properties of the material. The results show that the band structure of the perovskites AGeI{sub 3} (have a semiconductor behavior with direct band gap at R–R direction, the gap energy values calculated with mBJ-GGA, for each compound as following: 0.58, 0.63, and 0.71 eV, respectively. The optical properties, such as real and imaginary parts of the dielectric functions, refractive index, reflectivity, conductivity and absorption coefficient are investigated. As results, these compounds are competent candidates photovoltaic application like light harvester.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Spectroscopic and mechanical studies of lithium aluminoborate glasses doped with chromium ions

Aluminoborate glasses, doped with chromium ions, were prepared using melt quenching technique. Spectroscopic and mechanical tools were utilized to study the impact of B{sub 2}O{sub 3} substitution with Al{sub 2}O{sub 3} on the structure of the glass system. Infrared spectra uncovered that substitution of B{sub 2}O{sub 3} with Al{sub 2}O{sub 3} causes concealment of non-bridging oxygen NBOs and creation of inflexible AlO{sub 4} tetrahedral. The UV–Vis absorption spectra demonstrated a blue-shift of the optical absorption edge with increasing Al{sub 2}O{sub 3} content. The optical band gap was found to increase, while the refractive index diminished with addition of Al{sub 2}O{sub 3} content. The calculated crystalline field Dq, Racah parameters (B and C) and Dq/B indicated the diminishment in inter-electron repulsion with increasing the covalency. In particular, a value of Dq/B larger than 2.3 assures that chromium ions are in strong ligand field sites. The elastic moduli increase with increasing Al{sub 2}O{sub 3} content, due to the reduction NBOs and, consequently, the increased average bond connectivity.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High-Q microsphere integrated with a tapered fiber suitable for biosensing applications

We propose a novel whispering gallery mode (WGM) microsphere resonator integrated with a tapered optical fiber. In the proposed structure, the surface of the silica microsphere is coated with a thin layer of Hafnia (Hafnium dioxide). The results from analytical and numerical simulations indicated that the WGMs can be efficiently excited with quality factors, Q, up to 1.9 × 10{sup 5} in a silica-coated microsphere with a diameter of 24.08 μm, coupled to a tapered silica fiber with 1 μm core radius. The sensitivity, S, and figure of merit, FOM, of the proposed structure were 69 nm/R.I.U (nanometers per refractive index unit) and 1.3 × 10{sup 7}, respectively. Integration of microspheres and coupling system with High-Q and Ultra-High-S can be used for various applications such as detection and biosensing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Effect of the electric field induced birefringence on the slab waveguide evanescent-wave sensor sensitivity

We have investigated the potential of using the E-field induced birefringence for improving the sensitivity of uniaxial anisotropic slab waveguide sensor based on evanescent wave interactions. LiNbO{sub 3} waveguide core was used as an example. We have calculated the sensor sensitivity formulas for the two kinds of modes propagating simultaneously in the waveguide sensor. In our study, we have distinguished between two different cases. The first case when the electric field is applied along the optic axis (+c) of the LiNbO{sub 3} wave guiding film (positive electric field); the second case when the electric field is applied opposite to the optic axis (−c) of such uniaxial crystal (negative electric field). The obtained results showed that, for positive electric field, increasing the electric field induces an increasing of the total anisotropy which causes decreasing on sensor sensitivity. However, for negative electric field, the increase of absolute values of negative electric field induces a decrease of the total anisotropy, the latter increases the sensor sensitivity. On the other hand, the study of the physical parameters on the sensor sensitivity showed that, to maximize the sensor sensitivity, it is advisable to use isotropic substrate that has a refractive index as closer as possible to the measurand index.

42 ENGINEERING↗
DOE OSTI2019

Evaluation of optical parameters and characterization of few layer sputtered MoS{sub 2} film by spectroscopic ellipsometry

The study involves spectroscopic ellipsometry analysis of sputter deposited few layer MoS{sub 2} grown on three different substrates (ITO coated glass, n-silicon and p-silicon) for diverse deposition time. We have investigated optical parameters such as refractive index, extinction coefficient and dielectric constant of MoS{sub 2} layers in the visible region of electromagnetic spectrum. For such purpose of investigation we have involved Cauchy dispersion model (for the film deposited on n-silicon and p-silicon) and hybrid of Lorentz and Drude model (for the film deposited on ITO coated glass). Furthermore, comparative analysis at the diverse growth time of 5, 10, 15 and 20 min has been performed on the basis of optical parameters and surface morphology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Composition dependence of structural and optical properties of Ge{sub x}Se{sub 100−x} semiconducting thin films

The studied thin films of Ge{sub x}Se{sub 100−x} compositions were synthesized with thermal evaporation technique at room temperature. The effect of composition on the structure of the prepared films was characterized by X-ray diffraction and scanning electron microscopy. The stoichiometry of the studied compositions was examined by energy dispersive X-ray spectroscopy. The film thickness and refractive index were calculated by Swanepoel’s method. The structural analysis showed that the as-prepared Ge{sub x}Se{sub 100−x} (x = 10, 15, 20 and 30 at.%) films exhibit the amorphous state while other films containing 25, 35 and 40 at.% of Ge are polycrystalline. On the other hand, the GeSe and Se crystalline phases are obtained for the annealed films. The analysis of the optical spectra showed that E{sub g} increases with increasing Ge content up to a x = 30 at.% and then decreases with further increase of the Ge concentration. Other many optical parameters such as optical conductivity, dispersion energy and dissipation factor were determined and strongly affected by the variation of the composition.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Influence of argon flow rate on structural and optical properties of transparent Nb{sub 2}O{sub 5} thin films

Transparent niobium pentoxide (Nb{sub 2}O{sub 5}) thin films deposited on glass substrates by RF sputtering at different argon (Ar) flow rate were contrastively studied. Analytical methods such as X-ray fluorescence, Fourier-transform infrared spectroscopy and field emission scanning electron microscope were utilized to investigate the morphological surface and structural properties of Nb{sub 2}O{sub 5} thin films deposited at different Ar flow rate. UV–Vis–NIR and photoluminescence (PL) spectroscopy were used to explore the optical properties of Nb{sub 2}O{sub 5} thin films deposited at different Ar flow rate. The allowed optical band gap (E{sub g}{sup d}) of the Nb{sub 2}O{sub 5} thin films varies from 3.88 to 3.80 eV with increasing Ar flow rate from 30 to 90 sccm. The PL of the Nb{sub 2}O{sub 5} thin films showed strong emission peak around 400 nm. The real values of the refractive index are increase with increasing Ar flow rate. Optical quantities related to the optical constants of Nb{sub 2}O{sub 5} thin films thin films such as single oscillator parameters and third-order nonlinear susceptibility were assessed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Ag-doped HfO{sub 2} thin films via sol–gel dip coating method

In this study, undoped and Ag-doped HfO{sub 2} thin films were deposited on glass substrates by means of sol–gel dip coating method. These films were then thermally annealed at 500 °C for 1 h. The structural and optical properties of undoped and Ag-doped HfO{sub 2} thin films were characterized by X-ray diffraction, UV–Vis spectrometry and scanning electron microscope. The results of this analysis were compared and interpreted with the results obtained in literature by various methods of coating with HfO{sub 2}. The X-ray diffraction peaks of the films paired with monoclinic HfO{sub 2} crystalline peaks. The refractive indices of the films decreased with doping Ag, at 500 nm wavelengths. The optical band gap values of Ag-doped HfO{sub 2} thin films increased with doping Ag. The porous structures were observed on the surface films, especially with 5% Ag doping.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

A new proposal for a high-performance 4-channel demultiplexer based on 2D photonic crystal using three cascaded ring resonators for applications in advanced optical systems

In this paper, a high-performance 4-channel demultiplexer (DEMUX) based on 2D photonic crystal using three cascaded ring resonators is proposed. The proposed DEMUX is composed of square lattice of silicon dielectric rods with a refractive index of 3.46 suspended in air. For the proposed device, the lattice constant a = 590 nm and the filling factor r/a = 0.2. In this study, the plane wave expansion and finite-difference time-domain methods are used respectively to characterize the photonic band gap and to investigate the optical behaviour of the structure. It is demonstrated that by choosing appropriate values for the radius of the inner rods, scattering rods, coupling rods and the coupling length between the bus and the drop waveguides, the desired wavelengths can effectively be separated. The resonant wavelengths of the proposed DEMUX are 1528.7 nm, 1535.3 nm, 1531 nm, and 1533 nm. The mean quality factor, spectral bandwidth and the transmission efficiency of our device are computed to be respectively 7358.5, 0.217 nm and 99.25%. The proposed DEMUX has a mean channel spacing, minimum and maximum values of crosstalk of about 2.2 nm, − 46.68 dB and − 9.79 dB, respectively. Furthermore, the footprint of the device is 294.4 μm{sup 2}, which is suitable for photonic integrated circuits.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Numerical investigation on a new designed hollow-core photonic crystal fiber with large modal separation

We investigate the characteristics of optical modes in a new designed hollow-core photonic crystal fiber (PCF) with large modal separation. The large effective refractive index difference between the adjacent second-order vector modes can be maintained higher than 0.001 within the wavelength range from 1 to 2 μm. The maximum value can arrive 0.01199 between HE{sub 21} and TM{sub 01} mode at 2 μm. The fundamental mode of the proposed PCF has flat dispersion in a wide spectral range, which can be applied on wideband supercontinuum generation. The influence on the characteristics by the PCF structure has also been investigated. The increase of the size of the central air hole and the duty cycle affects the flatness of the dispersion curve to some extent. Our simulated results could provide an optimized fiber structure for the experimental study on stable transmission of vector modes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Role of oxygen concentrations on structural and optical properties of RF magnetron sputtered ZnO thin films

We report an investigation on the effect of oxygen flow rate on the structural and optical properties of zinc oxide thin films prepared by RF magnetron sputtering. The structural measurements were carried using grazing incidence X-ray diffraction, atomic force microscopy and Raman spectroscopy. The role of oxygen partial pressure on the crystallinity, the surface morphology and vibrational modes has been established. The optical properties of the films were investigated using FR-Basic-VIS/NIR fitted with FR-Monitor software for film thickness, refractive index and color determination. The film thickness is observed to increase when oxygen is introduced at 4 sccm but eventual decrease with increase in the flow rate an indication of initial increase in rate of deposition followed by reduction. Elaborate explanations of these trends are provided.

36 MATERIALS SCIENCE↗
DOE OSTI2019

First principle study of structural, electronic, optical, and transport properties of ternary compounds NaGaX{sub 2} (X = S, Se, and Te) in tetragonal chalcopyrite phase

Eemploying the all electron full potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method based on density functional theory (DFT) structural, electronic, optical, and transport properties of compounds NaGaX{sub 2} (X = S, Se, and Te) in tetragonal phase have been investigated at ground state. The exchange-correlation effects have been included using the Wu Cohen (WC) generalized gradient approximation (GGA) and modified Becke–Johnson (mBJ) exchange potentials. Enthalpy of formation values ensure that crystal structures are stable in tetragonal chalcopyrite phase. Total and partial density of states, and band structures have been plotted to calculate electronic properties which exhibits direct band gap for all compounds. The electronic band gap of NaGaS{sub 2} (2.1 eV) is found to be higher than the electronic band gaps of NaGaSe{sub 2} (1.7 eV) and NaGaTe{sub 2} (1.2 eV) compounds. Using real and imaginary parts of the dielectric function, optical properties such as refractive index (n), extinction coefficient (k), reflectivity (R), absorption coefficient (α), and energy loss spectrum (L) were determined. Transport properties like Seebeck coefficient, thermal and electrical conductivities, figure of merit, and power factors have also been reported by combining the results from DFT and Boltzmann transport theory. The high absorption peaks in visible and ultraviolet regions of the energy spectrum and direct band gaps of these compounds ensure that three compounds are promising materials for photovoltaic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Synthesis and study of optical properties of copolymers of perfluoro-2,2-dimethyl-1,3-dioxole and perfluoro(propyl vinyl ether)

Polymerization under ultrahigh pressure without involvement of initiators was used to synthesize amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole and perfluoro(propyl vinyl ether). The copolymers have molecular masses within 2•10{sup 4}—7•10{sup 4} au, possess high optical transparency in the telecom ranges of wavelength at 0.85, 1.3, and 1.5 μm and very low refractive index n = 1.293—1.314 at the wavelength λ = 632.8 nm. They can form films and are promising as claddings for optical fibers and waveguides. Amorphous films with the thickness of 1—4 μm were prepared by spin-coating from solutions of the perfluorinated copolymers in perfluorodecalin.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Absorption Spectra of Gold Nanoparticle Suspensions

Three gold nanoparticle suspensions are obtained, and mean radii in distributions – (6.1 ± 0.2), (11.9 ± 0.3), and (17.3 ± 0.7) nm – are determined by the transmission electron microscopy method. The optical absorption spectra of suspensions are obtained and studied. Calculation of spectral dependences of the absorption index of suspensions at values of the gold complex refractive index taken from the literature showed a significant deviation of experimental and calculated data in the region of 450–800 nm. Spectral dependences of the absorption of suspensions are simulated within the framework of the Mie–Drude theory taking into account the interband absorption in the form of an additional term in the imaginary part of the dielectric permittivity of the Gaussian type. It is shown that to quantify the spectral dependences in the region of the plasmon absorption band of nanoparticles, correction of the parameters of the interband absorption is necessary in addition to the increase of the relaxation parameter of the Drude theory. Spectral dependences of the dielectric permittivity of gold in nanodimensional state are refined from the solution of the inverse problem. The results of the present work are important for predicting the special features of operation of photonic devices and optical detonators based on gold nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Holographic Formation of Diffraction Elements for Transformation of Light Beams in Liquid Crystal – Photopolymer Compositions

A theoretical model of holographic formation of diffractive optical elements for transformation of light beam field into Bessel-like fields in liquid crystal – photopolymer (LC–PPM) composite materials with a dyesensitizer is developed. Results of numerical modeling of kinetics ofvariation of the refractive index of a material in the process of formation with different relationships between the photopolymerization rates and diffusion processes are presented. Based on the results of numerical simulation, it is demonstrated that when the photopolarization process dominates, the diffractive element being formed is distorted. This leads to a change in the light field distribution at its output and consequently, to ineffective transformation of the reading beam. Thus, the necessity of optimizing of the recording conditions and of the prepolymeric composition to increase the transformation efficiency of light beam fields is demonstrated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Influence of After-Growth Treatments on the Optical Parameters of Teraherz ZnGeP{sub 2} Crystals

Results of investigations are presented of the THz spectra of the refractive index n(v) and of the extinction coefficient k(v) for ZnGeP{sub 2} single crystals with different degrees of technological treatment – after growth by the vertical Bridgman technique, after heat treatment at temperatures above the Debye temperature for the highest-frequency phonons, and after modification of the single-crystal properties under irradiation by fast electrons (~4 MeV).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗