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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Radiative Transfer, Non-transparency, Stability Against Quench in Superconductors and Their Correlations

Radiative transfer calculations are presented for multi-filamentary BSCCO 2212 and 2223 and for thin film-coated YBaCuO 123 superconductors. A strictly radiative view allows conductor morphology of these superconductors to be interpreted as particulate or quasi-particulate objects. Problems then arising from non-regular particle shape, missing refractive indices, dependent scattering and superconductor material (diamagnetic) properties are solved in a multi-step, approximation approach. Both types of conductors are shown to be non-transparent to mid-IR radiation. Non-transparency may become critical for superconductor stability. The obtained extinction cross sections converge near the phase transition. A substantial difference of extinction properties between the superconducting and normal conducting state thus cannot be observed. As a first corollary from non-transparency, application of the additive approximation for the total thermal conductivity used in previous numerical calculations of the BSCCO and YBaCuO superconductors is confirmed. Second, within transit time intervals, the length of which depends on optical thickness, no uniform equilibrium conditions of electron pair density within the conductor cross section and near critical temperature are observed. Phase transition does not proceed uniformly, neither spatial nor temporal, and the order (succession on time scales) of local events (temperature variations, quench), in extreme cases, is completely dissolved. As another corollary, non-transparency even makes the existence of uniquely defined, physical time scales doubtful in a superconductor. The obtained results are expected to improve existing stability models and will be of practical value for future materials development.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Optical Properties of Planar and Annular Ternary Superconducting Photonic Crystals in Near-Zero-Permittivity Operation Range

Optical properties of ternary superconducting planar/annular photonic crystals composed of a high-temperature superconductor and two dielectrics were theoretically investigated based on transfer matrix methods in Cartesian and cylindrical coordinates. Electrodynamics of superconductor were modelled using two-fluid model. It is of interest to observe that, for a planar structure, there exists an additional high reflectance band termed as superpolariton gap near the superconducting threshold wavelength for the TM wave at oblique incidences and some reflection dips also were found in the TM reflectance. However, the superpolariton gap and reflection dips were seen for an annular geometry at higher order azimuthal number. For an annular structure, the size of superpolariton gap can be controlled by simply adjusting the starting radius. Moreover, the superpolariton gap in both structures strongly depends on the operating temperature, different combinations of dielectric refractive indices, and thicknesses of dielectric materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Nanoparticle using parallel split rings and implementation of chain for creating Fano resonance with polarization independence for energy harvesting in mid-infrared

In optical devices, the polarization of the incident wave affects the Nano particle characteristics. Therefore, designing a polarization-independent device is significant in the process of designing optical structures. On the other hand, the concept of Fano resonance and dark mode has been utilized for achieving more energy enhancement. In this paper, we have developed a symmetrical Nano antenna by employing Fano resonance, which is independent of the incident wave polarization. The proposed Nano antenna is modified in mid infrared regime for biosensing and energy harvesting applications. The designed metamaterial antenna is made by Nano split ring resonators with etched capacitive gaps, which are utilized for concentrating energy. The introduced Nano antenna has a bright and dark mode with a weak enhancement of electric field. The effect of the incident wave polarization is investigated at wave incident angles between 0° and 45° to illustrate the independency of the polarization due to the symmetrical shape of the Nano antenna. In order to trigger the dark mode and enhance the electric field, a Nano chain is incorporated in the final structure. This arrangement has led to increasing of electric field drastically. Furthermore, the figure of merit has been calculated as an advantageous factor in sensing the surrounding materials with various refractive indices. Our findings illustrated that the chain arrangement has caused a peak in the linear form of the extinction cross section of the Nano antenna. This in turn has resulted in the appearance of Fano resonance with no impact on the resonance frequency that has been originally adjusted by capacitive gaps and inductive strips.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Enhanced sensitivity of hemoglobin sensor using dual-core photonic crystal fiber

A Hemoglobin (Hb) biosensor based on dual-core photonic crystal fiber is proposed and analyzed. In this paper, the effective refractive index dependency on the Hb concentration within a blood sample is utilized in obtaining the transmission spectrum variation. The results are calculated using full vectorial finite element method. Through this study, the effect of the structure geometrical parameters on the sensor performance is optimized to maximize the sensor sensitivity. The numerical results show a sensitivity of 8.013 nm/g/dL for the X-polarized mode at 3.7 cm fiber length and 7.68 nm/g/dL for the Y-polarized mode at 3.2 cm fiber length of the proposed sensor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Design and analysis of multi-hexagonal reversible encoder using photonic crystals

In this paper, a 4 × 2 reversible encoder with hexagonal lattice has been designed using two-dimensional photonic crystals with non-linear refractive index. In order to demonstrate the working of the encoder, we have used the multi-hexagonal shaped structure arranged in parallel with appropriate inclination to get the desired output. During its functionality as an encoder, more than 98% of the power is coupled at the output port to obtain logic 1 and less than 17.2% of the power is coupled for obtaining logic 0. In addition, during its functionality as a reversible encoder, the logic 1 and logic 0 correspond to 97.5% and 15.1%, respectively. The proposed encoder provides an improved contrast ratio of 12.18 dB and 11.5 dB for logical states of 01 and 10, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Design and engineering of dispersion and loss in photonic crystal fiber 1 × 4 power splitter (PCFPS) based on hole size alteration and optofluidic infiltration

We have presented a technique based on optofluidic infiltration and air-holes diameter variation together to design a 1 × 4 photonic crystal fiber power splitter (PCFPS) which have very low dispersion (D): (0 ≤ D ≤ 2.5 (ps/nm/km) and very low loss (L): 0 ≤ L ≤ 0.025(dB/cm) in a wide range of wavelengths (1100–1700 nm). This approach allows us to control the dispersion of the fundamental mode in a PCF beam splitter by choosing appropriate refractive indices for liquids and suitable diameters for air-holes in PCF power splitter. In fact, the techniques, used in this paper are complementary of each other and give us more excellent results which are better than other reported results in researchers’ works so far. In this work, a new design of 1 × 4 photonic crystal fiber power splitter is proposed by using beam propagation method. An optical Gaussian signal at a wavelength of third communication window range (1550 nm) is inserted into the central core and equally is divided into four core (25% of the total input power interred to each core). In addition, the physical behavior of coupling characteristics is obtained by using coupled mode analysis. Numerical simulations show that input optical signal can be equally divided in photonic crystal fiber structure with low dispersion and low loss. The total size of proposed PCFPS is 30 µm × 30 µm × 1.2 mm, too.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Design of graphene-based hybrid waveguides for nonlinear applications

The extraordinary properties of a monolayer graphene can be effectively utilized in integrated optoelectronic devices. Therefore, the optical properties and the effective parameters on the graphene’s conductivity are calculated at the telecom wavelength 1.55 µm. Next, the different types of photonic and plasmonic hybrid waveguides based on graphene are designed for nonlinear applications such as frequency conversion processes. The fundamental proposed structure consists of a LiNbO{sub 3} layer, a single graphene layer and a dielectric gap between the graphene and LiNbO{sub 3} to support the nonlinear applications such as second harmonic generation. The waveguide’s performance is analyzed in terms of the intensity of electric field, LiNbO{sub 3} thickness, the gap refractive index, mode effective index and propagation loss while the graphene’s chemical potential is varied with an applied gate voltage. According to the results, a sudden rise in propagation loss at µ{sub c} = 0.493 eV (where the permittivity of graphene is almost zero) is observed. At last, a plasmonic hybrid waveguide consisting of a silver strip and a graphene layer placed between the metal and LiNbO{sub 3} layer is presented and the effect of the graphene’s chemical potential on the mode effective index and the propagation length are studied.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Absorbing boundary condition (ABC) and perfectly matched layer (PML) in numerical beam propagation: a comparison

The absorbing boundary condition (ABC) and the perfectly matched layer (PML) are employed to suppress the numerical reflections in wave propagation methods. The PML has earlier been shown to fail at the grazing angle propagation of beam. The ABC is preferred over the PML where refractive index is not an analytic function. We have explored the performance of the ABC in reflection-less absorption of non-paraxial propagation of beams and have compared it against the PML. We have considered an example of the propagation of Gaussian beams through a homogeneous medium terminated with ABC or PML. We have used the collocation method for propagation. We have found that both the boundary conditions are comparable in performance. The ABC performed relatively better than the PML for beams at smaller angles. However, the performance of the PML is better than that of the ABC at larger tilt angles.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

A simulation study on chaotic behavior of light propagation in graded index fiber under random perturbation

Chaotic behavior of optical rays in a graded index fiber is studied with the help of nonlinear dynamical method under random perturbation of refractive index. The study indicates that behavior of the rays evolves from regular to chaotic due to the random perturbation. This causes irregularity of propagation of the rays in the graded index fiber, and then the performance of the fiber is reduced.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Efficient coupling of dynamic electro-optical and heat-transport models for high-power broad-area semiconductor lasers

In this work, we discuss the modeling of edge-emitting high-power broad-area semiconductor lasers. We demonstrate an efficient iterative coupling of a slow heat transport (HT) model defined on multiple vertical–lateral laser cross-sections with a fast dynamic electro-optical (EO) model determined on the longitudinal–lateral domain that is a projection of the device to the active region of the laser. Whereas the HT-solver calculates temperature and thermally-induced refractive index changes, the EO-solver exploits these distributions and provides time-averaged field intensities, quasi-Fermi potentials, and carrier densities. All these time-averaged distributions are used repetitively by the HT-solver for the generation of the heat sources entering the HT problem solved in the next iteration step.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Gaussian beam scintillation index for slant path in weak turbulence: closed form expressions

The scintillation index (SI) is an important issue in studying the effect of the atmospheric turbulence in the light waves. With the Rytov weak fluctuation theory, the SI is commonly referred to the Rytov parameter. The previous studies dealt with the plane wave and spherical wave models. Each of these gives an idea of how an optical beam will react to turbulence but are not realistic. One is infinitely long, while the other is an infinitesimal point source. The Gaussian beam wave is the most realistic of the optical waves, but also the most complex to use for calculations. In this paper, a closed form expression for Gaussian beam SI propagation in slant path and through weak fluctuation is derived using the polynomial model of the refractive index structure parameter. The slant path SI model of the plane and spherical waves can be generated from the SI expression of Gaussian beam. The analytic expressions are obtained and are then used to analyze the effect of propagation distance, transmitter/receiver heights, and elevation angle on the SI. Signal to noise ratio and bit error rate are calculated for performance evaluation showing a significant enhancement at elevation angles greater than 45°.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Comparative analysis of silicon and black phosphorous as an add-layer in nanomaterial based plasmonic sensor

In the proposed article silicon and black phosphorous as an add-layer above the plasmonic metal in nanomaterial (graphene and MoS{sub 2}) based plasmonic sensor are compared. The reflectance curves are obtained for different thickness of silicon and black phosphorous by using transfer matrix method. The performance defining parameters i.e. shift in resonance angle, beam width of reflectance curve, and minimum reflectance intensity for a minute change of 0.005 in refractive index of sensing medium at the optimized thickness 5 nm of silicon and black-phosphorous, and conventional are (13.86, 10.96, 2.415), (4.956, 3.817, 1.419), and (0.012, 0.002, 0.002) respectively. Further, the addition of nanomaterials increases these parameters and generally follows the order MoS{sub 2}-graphene > MoS{sub 2} > graphene. Furthermore, transverse-magnetic electric field shows that nanomaterial covered silicon have higher penetration depth than the nanomaterial covered black-phosphorous. The analysis shows that nanomaterial covered silicon can replace nanomaterial covered black-phosphorous in terms of higher sensitivity and penetration depth.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

The properties of a tunable terahertz multichannel filter from one-dimensional photonic crystal dope by magnetized plasma defect

The terahertz magnetize-field tunable filtering properties in a multichannel filter based on a one-dimensional photonic crystal doped by magnetized plasma are theoretically investigated. The considered structure of (AB){sub 4}(ACB){sub N}(AB){sub 4} is designed, where A and B are two dielectric layers, C is the plasma layer, and N is the defect number. First, the structure can be worked as a multichannel filter whose channel number equals N. Second, the defect mode frequencies are all red-shifted as the ratio of dielectric refractive index or the sum of the A and B layer length increases. Third, we find that the channel frequencies can be shifted as a function of the applied magnetic field and the defect mode frequencies are all red-shifted as the plasma density increases. And the thickness of a plasma layer also affects the intensity, position and number of the defect modes. Therefore, these unusual properties may provide a novel design idea of a tunable terahertz multichannel transmission filter in future.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of light polarization in photonic nanojet

Illumination plays a key role in getting high resolution imaging. Photonic nanojet is a new lighting system. Since the transverse beam width of the nanojet can reach λ/3, photonic nanojet is usually considered to be the key point for the explanation of the high-resolution microsphere assisted microscopy. However, the polarization of photonic nanojet are usually out of attention. In this work, we investigate the photonic nanojets formed by illuminating a dielectric microcylinder by two plane waves with different linear polarizations. The influences of wavelength and refractive index contrast between the microcylinder and its surrounding, and the cases illuminated by the Gaussian beam are also studied. Numerical results demonstrate that the TM polarization can generate a wider nanojet waist than the TE polarization, and this is produced by the longitudinal component of the TM-polarization illumination. When the Gaussian beam width becomes larger than diameter of the cylinder, the nanojet waists become smaller than that obtained by the cylinder under a plane wave. At last, the reason why the TE polarization has a thinner nanojet waist is given, it is related to the longitudinal component making light transmission far away from optical axis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Cell culture medium and nano-confined water on nonlinear optical properties of Congo Red

Optical properties of Congo Red in the solvents and nano-confined water can be studied using techniques, including Z-scan, spectrophotometer and photon correlation spectroscopy The absorbance of Congo Red depends on environmental conditions that were considered as the rules of dielectric constant and solubility. The solubility of Congo Red in the solvent and of dye-water in nano-confined water determines the value of both nonlinear absorption and refractive index. The nonlinear optical properties of AOT/n-Decane/H{sub 2}O are higher than AOT/Toluene/H{sub 2}O. The photon correlation spectroscopy findings show higher dye aggregation in AOT/Toluene/H{sub 2}O in comparison with AOT/n-Decane/H{sub 2}O. According to the results, the nonlinear optical properties of Congo Red are enhanced by increasing the dye solubility in the nano-confined water, as well as the dye solubility changes in microemulsion by oil length scale and polarity. Incremental concentration of cell culture medium enhanced the nonlinear optical properties of Congo Red in nano-confined water.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Improvement of the performance parameters of the surface plasmon resonance biosensor using Al{sub 2}O{sub 3} and WS{sub 2}

Here, proposed Kretschmann configuration based surface plasmon resonance biosensor shows immense improvement in its performance parameters. This highly sensitive biosensor provides a higher value of quality factor and detection accuracy. We presented a five-layer model of a biosensor with two dimensional transition metal di-chalcogenides Tungsten disulfide (WS2) in addition with Al2O3 layer. By using one layer of WS2 with six layers of Al2O3, the highest sensitivity (227.5 °/RIU), detection accuracy (1.1123), and quality factor (28.26 RIU{sup −1}) can be achieved. CaF2 as coupling prism has also played a remarkable role in enhancing the performance parameters for its low refractive index.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Prepared σ-MnO{sub 2} thin films by chemical bath deposition methods and study of its optical and microstructure properties

In this work, σ-MnO{sub 2} thin films deposited by chemical bath deposition method at three concentration of solution. The influence of concentration on thickness, micromorphology and optical parameters were investigated by XRD, SEM, UV–Vis spectrophotometer, atomic force microscopic and multifractal analyses. The optical band gap of thin films is decreased with increase in concentration. The optical parameters: refractive index and real part of dielectric constant are increased with increase in concentration, but decrease in extinction coefficient and imaginary parts of dielectric constant are observed. The micromorphology and roughness of layers surface are changed as function of concentration. The studied samples have multifractal properties and can be included in computer algorithms useful for graphical representation of 3-D microtexture surfaces of σ-MnO{sub 2} thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Optical and photoluminensce properties of Eu{sup 2+}-activated strontium magnesium silicate phosphors using different rare earth co-activators

Nanostructured powders of Sr{sub 1.96}MgSi{sub 2}O{sub 7}:Eu{sub 0.01}{sup 2+}, R{sub 0.01}{sup 3+} (R{sup 3+ }= Er{sup 3+}, Tm{sup 3+} and Tb{sup 3+}) have been fabricated via urea combustion technique. XRD results implied that tetragonal Sr{sub 2}MgSi{sub 2}O{sub 7} was the major phase whereas monoclinic Sr{sub 2}SiO{sub 4} and SrSiO{sub 3} were the minor phases. Meanwhile, field emission SEM textures showed the hollow spherical network-like shape structures filled with fused interconnections for the Sr{sub 1.96}MgSi{sub 2}O{sub 7}:Eu{sub 0.01}{sup 2+} sample. It has been recognized that the replacement of Sr{sup 2+} with co-dopant R{sup 3+} ions e.g. Er{sup 3+}, Tm{sup 3+} and Tb{sup 3+} considerably help obtaining homogeneous structure as well. The values of band gap energy and calculated refractive index were ultimately dependant on the ionic radius of R{sup 3+} co-doping ion. It has been suggested that the divalent activator ion (Eu{sup 2+}) was responsible for the number of PL emission spectra, while the trivalent co-activator ions (R{sup 3+}) were the key reasons for variations in the broadening and intensity of PL emission spectra.

77 NANOSCIENCE AND NANOTECHNOLOGY↗