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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Resolvent-Techniques for Multiple Exercise Problems

We study optimal multiple stopping of strong Markov processes with random refraction periods. The refraction periods are assumed to be exponentially distributed with a common rate and independent of the underlying dynamics. Our main tool is using the resolvent operator. In the first part, we reduce infinite stopping problems to ordinary ones in a general strong Markov setting. This leads to explicit solutions for wide classes of such problems. Starting from this result, we analyze problems with finitely many exercise rights and explain solution methods for some classes of problems with underlying Lévy and diffusion processes, where the optimal characteristics of the problems can be identified more explicitly. We illustrate the main results with explicit examples.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Optical Properties of Amorphous Perfluorinated Polymers in the Terahertz Range

Novel amorphous perfluorinated polymers are synthesized and characterized using terahertz (THz) and x-ray spectra. The polymerization of such polymers in which all H atoms are replaced by F is examined. Their optical properties in the THz range show a record low index of refraction for solids in this range. The minimal possible index of refraction for such polymers is estimated. These materials are demonstrated to be highly transparent. The position of a weak absorption maximum in the range 1–2 THz is compared with the characteristic distance between the polymer structural elements that is obtained from an x-ray diffraction analysis of these materials.

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

Effect of Pressure on the Electronic, Magnetic, and Optical Properties of the In{sub 0.75}Cr{sub 0.25}P Compound

Using the density functional theory (DFT) approach and full-potential linearized augmented plane waves (FP-LAPW) method, some of the electronic (density of states, band structure, and Fermi surfaces), magnetic (total and local magnetic moments, spin polarization, exchange constants), and optical properties (dielectric function, energy loss function, and refractive index) were investigated. The GGA + U approximation was used for the exchange-correlation term. The effect of hydrostatic pressure up to 20 GP has been studied on these properties. The results show that the In{sub 0.75}Cr{sub 0.25}P compound is a half metal with 100% spin polarization at the Fermi level and the increment of pressure does not change its half-metallic behavior. The half-metal gap achieved for this compound is variable between 1.38 and 1.5 eV. The interaction between Cr and P atoms in this compound is an anti-ferromagnetic type. It was observed that the total magnetic moment for this compound is about 3 μ{sub B}. Local magnetic moments change with increasing pressure, but the total magnetic moment remains unaffected by increasing the pressure. Calculations of the optical properties of the In{sub 0.75}Cr{sub 0.25}P compound showed that the dominant mechanism for the low-energy photons is due to the induced free carriers of the Cr atom, and the optical properties of this compound, in particular the refractive index in the visible region, change with increasing pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Thermally induced dispersive optical bistability in silver nanosuspensions produced by pulsed laser ablation method

The thermally induced optical bistability in prepared silver (Ag) nanosuspensions have been studied experimentally, using Fabry–Perot and Mach–Zehnder interferometry methods. Two Ag nanosuspensions of different sizes were produced by different fluences of pulsed laser ablation method in distilled water. The pulsed Nd:YAG laser of 7 ns pulse width, 1064 nm wavelength and different fluences was employed to produce Ag nanosuspensions. Experimental observations were performed by an ultraviolet–visible–near infrared spectrophotometry. Structure and size of prepared Ag nanoparticles were diagnosed using transmission electron microscope images. Fabry–Perot and Mach–Zehnder interferometry methods were used to carry out the optical bistability process in prepared Ag nanosuspensions. In two considered interferometers, the obtained phase shifts of the hysteresis loops based on the optical bistability are inversely proportional to the nonlinear refractive index of samples and thickness of Ag nanosuspensions cells. Results indicate that the induced thermal effect of the optical bistability can be tuned by modifying parameters such as the nonlinear refractive index and applied interferometry methods. Hence, a desirable situation for the thermo-optical effects of the optical bistability can be easily realized in Ag nanosuspensions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Optical characterization of nanostructured Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) films

The paper reports the optical properties of thin films of nanostructured Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) glassy alloys. The glassy alloys of Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) were prepared using melt quenching method. Thin films of nanostructured Ge{sub 1 − x}Sn{sub x}Se{sub 2.5} (x = 0, 0.3, 0.5) glassy alloys were prepared using physical vapor deposition method. The films were characterized using XRD, EDX and TEM, which confirmed the amorphous nature, composition and formation of nanorods in the samples. Absorption and transmission spectra of thin films were recorded in the spectral range 400–2500 nm to obtain energy band gap, refractive index, extinction coefficient, dielectric constant etc. Results show that refractive index increases while band gap decreases on increase of Sn content in the Ge–Se system. This is due to the increase in density of defect states within band gap. The values of Urbach energy support the obtained results.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Highly sensitive SPR PCF biosensors based on Ag/TiN and Ag/ZrN configurations

We numerically present and analyze a surface plasmon resonance (SPR) bimetallic photonic crystal fiber (PCF) biosensor using full vectorial finite element method. The bimetallic configuration is based on Silver and (TiN or ZrN) as alternative plasmonic materials. The reported design relies on PCF with an external channel to house the analyte. The inner surface of the channel is coated by a silver layer followed by TiN or ZrN to protect the silver layer from oxidation. The proposed biosensor can be implemented to detect the unknown analytes, organic chemicals, biological analytes, and biomolecules via the sensitive resonant peaks to the analyte refractive index variations for both polarized modes with high linearity. In this study, a comparison is made between the Ag/TiN configuration and the Ag/ZrN counterpart in terms of sensitivity, losses, and linearity. The geometrical parameters are optimized to achieve high refractive index sensitivities of 7000 nm/RIU for quasi-transverse electric (TE) mode and 6900 nm/RIU for quasi-transverse magnetic (TM) mode, respectively for the Ag/TiN configuration. However, the quasi TE and quasi TM modes achieve high sensitivity of 5300 and 5400 nm/RIU, respectively using the Ag/ZrN configuration. The standard PCF fabrication technologies can be used to fabricate the proposed SPR PCF biosensors.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Designing a high sensitivity hexagonal nano-cavity photonic crystal resonator for the purpose of seawater salinity sensing

In this paper a sensing platform based on nano-cavity photonic crystal resonator (NC-PCR) is proposed for seawater salinity concentration detection. It has been demonstrated that the proposed NC-PCR has high sensitivity and selectivity for various concentrations of seawater salinity. The sensitivity is computed to be as high as 544 nm/RIU (nm per refractive index unit) and the quality factor (Q) is 3860. Also it has been shown that the figure of merit for the proposed structure calculated to be as high as ~ 1.234 × 10{sup 3} RIU{sup −1} which is very appropriate for sensing applications. Moreover, the minimum detection limit for the presented structure is obtained as 8.1 × 10{sup −5} RIU. The finite-difference time-domain method is employed to investigate the transmission characteristics of the device for a verity of refractive indices. It should also be mentioned that our design is comparatively easy to fabricate and certainly the advantages of our design justify its usage in sensing applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Design and fabrication of ring resonator spectral response through-drop wavelengths selective

In this paper, we discuss the basic characteristics of the SOI based micro-ring resonator, and understand the influence of the high refractive index difference and the small size on the spectral characteristics of the ring resonator. The novelty and importance of the spectral response selectivity of ring resonators is driven by the grating couple technique. This advantage is the periodic variation of the refractive index in the coupled grating, which will result in the coupling of the conduction wave modes. By means of measurement and simulation, observe the changes and trends of the spectrum in steady state and transient state, and finally analyze the performance of the ring resonator in the application of signal processing. It achieves polarization-independent grating couplers with high efficiency, wide bandwidth and low polarization-dependent loss at around the 1560 nm optical communication band. Drop end set laser wavelength correction 1591.9 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation of resonant mode sensitivity in PhC based ring resonators

Quality factor and refractive index sensitivity are significant parameters in designing optical devices based on ring resonators such as filters, demultiplexers, switches in which the ring resonator is considered as an elementary componant. In this paper, we propose a photonic crystal ring resonator with super-ellipse shaped core. The proposed ring resonator placed between two parallels waveguides (bus waveguide and drop waveguide). The transmission efficiency of the proposed ring resonator at λ = 1547.3 nm is about 95% with bandwidth and quality factor values equal to 0.7 nm and 2210, respectively. Simulation results show that the resonance sensitivity upon refractive index variation of coupling, outer layer, adjacent and scattering rods are Δλ/Δn = 0.2 nm/0.01, Δλ/Δn = 0.225 nm/0.01, Δλ/Δn = 0.125 nm/0.01 and Δλ/Δn = 0.05 nm/0.01, respectively. The finite different time domain and plane wave expansion methods are used to calculate the outputs spectrum and band gap, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Preparation of Cu–Fe–O thin films via post oxidation of iron/copper bilayers: structural, optical and electrical properties

Cu–Fe–O thin films were prepared via vacuum thermal evaporation of Fe and Cu after what the obtained bilayer Fe\Cu was annealed in free air at different temperatures during 2 h. The obtained Cu–Fe–O thin films were characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), electrical and spectrophotometric measurements. X-ray diffraction (XRD) analysis revealed the presence of Fe{sub 2}O{sub 3}, CuO and CuFeO{sub 2} phases. Cu–Fe–O thin films exhibit rough surfaces by analyzing the film morphologies by scanning electron microscopy. Energy dispersive spectroscopy (EDS) technique was used to evaluate Cu–Fe–O thin films stoichiometry. The optical properties reveal that the absorption coefficient of Cu–Fe–O thin films is larger than 10{sup 5} cm{sup −1} and two optical direct band gaps in the range 1.65–2.2 eV were found. The Wemple and DiDomenico model was used to study the dispersion of the refractive index in terms of the single oscillator model. So, optical parameters such as refractive index, extinction coefficient, oscillator energy and dispersion energy were calculated. In addition and by using the model of Spitzer and Fan, the electrical free carrier susceptibility and the carrier concentration on the effective mass ratio were evaluated. All the samples present relatively high electrical resistivity.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Fano resonances based on plasmonic square resonator with high figure of merits and its application in glucose concentrations sensing

A compact plasmonic structure is proposed employing symmetrical metal–insulator-metal (MIM) waveguides coupled to the square resonator for nano-sensing applications, especially for water glucose sensing. Finite difference time domain method is chosen to derivate the output characteristics and magnetic-field distributions. Outcomes illustrate the Fano resonance in the output characteristics can be simply managed by varying the inner and outer lengths and the refractive index of the square cavity. Also, between Fano resonance wavelength and resonator length, a linear behavior exists. These features suggest that physical parameters provide flexibility to propose the structure. Our plasmonic device produces a sensitivity and figure of merit of about 6400 nm/RIU and 1 × 10{sup 4}, respectively. By utilizing the mathematical model for water refractive index, we aim to develop a sensor structure to detect the glucose concentration in water. This designed sensor may discover significant applications in future nanosensing domain.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Vacuum birefringence in strong magnetic fields: (I) Photon polarization tensor with all the Landau levels

Photons propagating in strong magnetic fields are subject to a phenomenon called the 'vacuum birefringence' where refractive indices of two physical modes both deviate from unity and are different from each other. We compute the vacuum polarization tensor of a photon in a static and homogeneous magnetic field by utilizing Schwinger's proper-time method, and obtain a series representation as a result of double integrals analytically performed with respect to proper-time variables. The outcome is expressed in terms of an infinite sum of known functions which is plausibly interpreted as summation over all the Landau levels of fermions. Each contribution from infinitely many Landau levels yields a kinematical condition above which the contribution has an imaginary part. This indicates decay of a sufficiently energetic photon into a fermion-antifermion pair with corresponding Landau level indices. Since we do not resort to any approximation, our result is applicable to the calculation of refractive indices in the whole kinematical region of a photon momentum and in any magnitude of the external magnetic field. - Highlights: Black-Right-Pointing-Pointer Vacuum birefringence is studied in the presence of externally applied magnetic field. Black-Right-Pointing-Pointer A general framework is given on the basis of a vacuum polarization tensor of photon. Black-Right-Pointing-Pointer A resummed vacuum polarization tensor is calculated analytically and exactly. Black-Right-Pointing-Pointer Contributions of all the Landau levels are obtained in the form of an infinite sum. Black-Right-Pointing-Pointer Threshold behavior of real-photon decay is obtained at the each Landau level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

A different method for calculation of the deflection angle of light passing close to a massive object by Fermat’s principle

We introduce a method for calculating the amount of deflection angle of light passing close to a massive object. It is based on Fermat’s principle. The varying refractive index of medium around the massive object is obtained from the Buckingham pi-theorem. Highlights: •A different and simpler method for the calculation of deflection angle of light. •Not a curved space, only 2-D Euclidean space. •Getting a varying refractive index from the Buckingham pi-theorem. •Obtaining the some results of general relativity from Fermat’s principle.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

A spherical aberration-free microscopy system for live brain imaging

Highlights: • Deep-C is an automatic spherical aberration compensation system for in vivo imaging. • Deep-C is composed of ZlinC and Peak-C. • ZlinC coordinates the correction collar rotation and the Z-position of an objective. • Peak-C is a scanning algorithm processor for calculation of image contrast. • Deep-C allows quantitative, reproducible analysis of fine GFP-labeled structures. The high-resolution in vivo imaging of mouse brain for quantitative analysis of fine structures, such as dendritic spines, requires objectives with high numerical apertures (NAs) and long working distances (WDs). However, this imaging approach is often hampered by spherical aberration (SA) that results from the mismatch of refractive indices in the optical path and becomes more severe with increasing depth of target from the brain surface. Whereas a revolving objective correction collar has been designed to compensate SA, its adjustment requires manual operation and is inevitably accompanied by considerable focal shift, making it difficult to acquire the best image of a given fluorescent object. To solve the problems, we have created an objective-attached device and formulated a fast iterative algorithm for the realization of an automatic SA compensation system. The device coordinates the collar rotation and the Z-position of an objective, enabling correction collar adjustment while stably focusing on a target. The algorithm provides the best adjustment on the basis of the calculated contrast of acquired images. Together, they enable the system to compensate SA at a given depth. As proof of concept, we applied the SA compensation system to in vivo two-photon imaging with a 25 × water-immersion objective (NA, 1.05; WD, 2 mm). It effectively reduced SA regardless of location, allowing quantitative and reproducible analysis of fine structures of YFP-labeled neurons in the mouse cerebral cortical layers. Interestingly, although the cortical structure was optically heterogeneous along the z-axis, the refractive index of each layer could be assessed on the basis of the compensation degree. It was also possible to make fully corrected three-dimensional reconstructions of YFP-labeled neurons in live brain samples. Our SA compensation system, called Deep-C, is expected to bring out the best in all correction-collar-equipped objectives for imaging deep regions of heterogeneous tissues.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

A computational method for the Helmholtz equation in unbounded domains based on the minimization of an integral functional

We study a new approach to the problem of transparent boundary conditions for the Helmholtz equation in unbounded domains. Our approach is based on the minimization of an integral functional arising from a volume integral formulation of the radiation condition. The index of refraction does not need to be constant at infinity and may have some angular dependency as well as perturbations. We prove analytical results on the convergence of the approximate solution. Numerical examples for different shapes of the artificial boundary and for non-constant indexes of refraction will be presented.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Synthesis, crystal growth, structural and physicochemical studies of novel binary organic complex: 4-chloroaniline-3-hydroxy-4-methoxybenzaldehyde

The solid-state reaction, which is solvent free and green synthesis, has been adopted to explore the novel compound. The phase diagram of 4-chloroaniline (CA) and 3-hydroxy-4-methoxybenzaldehyde (HMB) system shows the formation of a novel 1:1 molecular complex, and two eutectics on either sides of complex. Thermochemical studies of complex and eutectics have been carried out for various properties such as heat of fusion, entropy of fusion, Jackson's parameters, interfacial energy and excess thermodynamic functions. The formation of molecular complex was also studied by IR, NMR, elemental analysis and UV-Vis absorption spectra. The single crystal of molecular complex was grown and its XRD study confirms the formation of complex and identifies the crystal structure and atomic packing of crystal of complex. Transmission spectra of grown crystal of the complex show 70% transmittance efficiency with cut off wavelength 412 nm. The band gap and refractive index of the crystal of complex have also been studied. - Graphical abstarct: Exploiting phase diagram study and solvent free synthesis a novel compound was synthesized and its single crystal growth, atomic packing, energy band gap and refractive index were studied. Highlights: Black-Right-Pointing-Pointer Novel organic complex was synthesized using Green or solvent free synthesis. Black-Right-Pointing-Pointer Phase diagram study provided the information to identify the worthy composition of novel complex. Black-Right-Pointing-Pointer The single crystal of the sufficient size was grown from the ethanol solution. Black-Right-Pointing-Pointer Crystal analysis suggested that the covalent bond is formed between the two parent compounds. Black-Right-Pointing-Pointer The transmittance of the crystal was found to be 70% and it was transparent from 412 to 850 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

First-principles studies on linear and nonlinear optical effects in Ln{sub 4}GaSbS{sub 9} (Ln=Ce-Nd, Sm, Gd-Tm, Lu)

Density functional theory (DFT) calculations have been performed on electronic structures of 11 middle-infrared (mid-IR) nonlinear optical quaternary sulfides: Ln{sub 4}GaSbS{sub 9} (Ln=Ce-Nd, Sm, Gd-Tm, Lu). Our results show that Ln{sub 4}GaSbS{sub 9} are indirect gap semiconductors with a slight band gap increase from Ce to Lu. Their linear optical properties, including refractive index, absorption coefficient and energy loss function, as well as the nonlinear optical coefficients including static d{sub 31}, d{sub 32}, d{sub 33} and dynamic d{sub 32}, are calculated. More importantly, the strong SHG response of Ln{sub 4}GaSbS{sub 9} can be attributed to the electronic transitions from S 3p states in valence bands (VB) to Sb-S and Ln-S antibonding states (CB). - Graphical Abstract: Density functional theory (DFT) calculations on Ln{sub 4}GaSbS{sub 9} reveal their linear optical properties, including refractive index, adsorption coefficient and energy loss function, the nonlinear optical coefficients including static d{sub 31}, d{sub 32}, d{sub 33} and dynamic d{sub 32}, as well as the origins of the strong SHG response. Highlights: Black-Right-Pointing-Pointer First-principles studies on a newly discovered NLO active family Ln{sub 4}GaSbS{sub 9}. Black-Right-Pointing-Pointer Reports static SHG coefficients (d{sub 31}, d{sub 32}, d{sub 33}) and dynamic d{sub 32}. Black-Right-Pointing-Pointer Reveals the origin of the strong SHG response.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Top-seeded solution crystal growth of noncentrosymmetric and polar Zn{sub 2}TeMoO{sub 7} (ZTM)

A top-seeded solution growth (TSSG) method was used to grow large, centimeter size, crystals of Zn{sub 2}TeMoO{sub 7} (ZTM) – a noncentrosymmetric and polar material. A TeO{sub 2}–MoO{sub 3} mixture in combination with the parent compound was used as a flux. The morphologies of the crystals can be controlled by different rotation speeds. Optical spectra indicate that ZTM is transparent up to 5.25 µm with a UV absorption edge of 300 nm. In addition, the refractive index along the optical x, y, and z axes was measured at different wavelengths. - Highlights: • Zn{sub 2}TeMo{sub 2}O{sub 7} crystals were grown by top-seeded solution growth (TSSG) method. • The morphology of the single crystals is controllable by changing rotation speed. • Optical transmission spectra indicate Zn{sub 2}TeMo{sub 2}O{sub 7} has a broad transmission range. • Refractive index along optical axes was measured at different wavelengths.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗