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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Third-order nonlinear optical response of colloidal gold nanoparticles prepared by sputtering deposition

The nonlinear optical responses of gold nanoparticles dispersed in castor oil produced by sputtering deposition were investigated, using the thermally managed Z-scan technique. Particles with spherical shape and 2.6 nm of average diameter were obtained and characterized by transmission electron microscopy and small angle X-ray scattering. This colloid was highly stable, without the presence of chemical impurities, neither stabilizers. It was observed that this system presents a large refractive third-order nonlinear response and a negligible nonlinear absorption. Moreover, the evaluation of the all-optical switching figures of merit demonstrated that the colloidal nanoparticles prepared by sputtering deposition have a good potential for the development of ultrafast photonic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Self-focusing of a high-intensity laser in a collisional plasma under weak relativistic-ponderomotive nonlinearity

Self-focusing a laser beam in collisional plasma is investigated under the weak relativistic-ponderomotive nonlinearity. In this case, the plasma equilibrium density is modified and it causes generation of the nonlinearity due to the Ohmic heating of electrons, collisions, and the weak relativistic-ponderomotive force during the interaction of the laser beam with the plasma. Our theoretical and simulation results show that a significant nonlinearity in laser self-focusing can occur under the weak relativistic-ponderomotive regime for some appropriate simulation parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Nonlinear electron oscillations in a warm plasma

A class of nonstationary solutions for the nonlinear electron oscillations of a warm plasma are presented using a Lagrangian fluid description. The solution illustrates the nonlinear steepening of an initial Gaussian electron density disturbance and also shows collapse behavior in time. The obtained solution may indicate a class of nonlinear transient structures in an unmagnetized warm plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Nonlinear electron acoustic waves in presence of shear magnetic field

Nonlinear electron acoustic waves are studied in a quasineutral plasma in the presence of a variable magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary positively charged ion background. Linear analysis of the governing equations manifests dispersion relation of electron magneto sonic wave. Whereas, nonlinear wave dynamics is being investigated by introducing Lagrangian variable method in long wavelength limit. It is shown from finite amplitude analysis that the nonlinear wave characteristics are well depicted by KdV equation. The wave dispersion arising in quasineutral plasma is induced by transverse magnetic field component. The results are discussed in the context of plasma of Earth's magnetosphere.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Complex dynamics of a nonlinear voter model with contrarian agents

We investigate mean-field dynamics of a nonlinear opinion formation model with congregator and contrarian agents. Each agent assumes one of the two possible states. Congregators imitate the state of other agents with a rate that increases with the number of other agents in the opposite state, as in the linear voter model and nonlinear majority voting models. Contrarians flip the state with a rate that increases with the number of other agents in the same state. The nonlinearity controls the strength of the majority voting and is used as a main bifurcation parameter. We show that the model undergoes a rich bifurcation scenario comprising the egalitarian equilibrium, two symmetric lopsided equilibria, limit cycle, and coexistence of different types of stable equilibria with intertwining attractive basins.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Nonlinearity measure and internal model control based linearization in anti-windup design

This paper considers the problem of internal model control based linearization in anti-windup design. The nonlinearity measure concept is used for quantifying the control system degree of nonlinearity. The linearizing effect of a modified internal model control structure is presented by comparing the nonlinearity measures of the open-loop and closed-loop systems. It is shown that the linearization properties are improved by increasing the control system local feedback gain. However, it is emphasized that at the same time the stability of the system deteriorates. The conflicting goals of stability and linearization are resolved by solving the design problem in different frequency ranges.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Propagation of nonlinearly generated harmonic spin waves in microscopic stripes

We report on the experimental study of the propagation of nonlinearly generated harmonic spin waves in microscopic CoFeB stripes. Using an all electrical technique with coplanar waveguides, we find that two kinds of spin waves can be generated by nonlinear frequency multiplication. One has a non-uniform spatial geometry and thus requires appropriate detector geometry to be identified. The other corresponds to the resonant fundamental propagative spin waves and can be efficiently excited by double- or triple-frequency harmonics with any geometry. Nonlinear excited spin waves are particularly efficient in providing an electrical signal arising from spin wave propagation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Nonlinear acoustics experimental characterization of microstructure evolution in Inconel 617

Inconel 617 is a candidate material for the intermediate heat exchanger in a very high temperature reactor for the next generation nuclear power plant. This application will require the material to withstand fatigue-ratcheting interaction at temperatures up to 950°C. Therefore nondestructive evaluation and structural health monitoring are important capabilities. Acoustic nonlinearity (which is quantified in terms of a material parameter, the acoustic nonlinearity parameter, β) has been proven to be sensitive to microstructural changes in material. This research develops a robust experimental procedure to track the evolution of damage precursors in laboratory tested Inconel 617 specimens using ultrasonic bulk waves. The results from the acoustic non-linear tests are compared with stereoscope surface damage results. Therefore, the relationship between acoustic nonlinearity and microstructural evaluation can be clearly demonstrated for the specimens tested.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Wave–vortex interactions in the nonlinear Schrödinger equation

This is a theoretical study of wave–vortex interaction effects in the two-dimensional nonlinear Schrödinger equation, which is a useful conceptual model for the limiting dynamics of superfluid quantum condensates at zero temperature. The particular wave–vortex interaction effects are associated with the scattering and refraction of small-scale linear waves by the straining flows induced by quantized point vortices and, crucially, with the concomitant nonlinear back-reaction, the remote recoil, that these scattered waves exert on the vortices. Our detailed model is a narrow, slowly varying wavetrain of small-amplitude waves refracted by one or two vortices. Weak interactions are studied using a suitable perturbation method in which the nonlinear recoil force on the vortex then arises at second order in wave amplitude, and is computed in terms of a Magnus-type force expression for both finite and infinite wavetrains. In the case of an infinite wavetrain, an explicit asymptotic formula for the scattering angle is also derived and cross-checked against numerical ray tracing. Finally, under suitable conditions a wavetrain can be so strongly refracted that it collapses all the way onto a zero-size point vortex. This is a strong wave–vortex interaction by definition. The conditions for such a collapse are derived and the validity of ray tracing theory during the singular collapse is investigated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Investigation of the second-order nonlinear optical properties of Cs{sub 2}TeMo{sub 3}O{sub 12} single crystal

The complete set of second-order nonlinear optical (NLO) coefficients of Cs{sub 2}TeMo{sub 3}O{sub 12} single crystals were obtained using the Maker Fringe techniques. The NLO coefficients d{sub 32} and d{sub 33} were measured to be on the order of 6.8 and 6.5 pm/V, respectively. Irradiated by 1064 nm laser, the crystal is phase-matchable, and its effective nonlinear coefficient is 4.6 pm/V for type I phase matching at θ = 42.7°. The relationship between the second-order nonlinear properties and the crystal structure is also discussed. Considering its wide transmission range, phase matching, and large effective NLO coefficient, Cs{sub 2}TeMo{sub 3}O{sub 12} is a good candidate for IR NLO application.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Surface plasmon enhanced third-order optical nonlinearity of Ag nanocomposite film

We obtain a large third-order optical nonlinearity (χ{sup (3)} ≈ 10{sup −10}esu) of silver nanoparticles dispersed in polyvinyl alcohol/tetraethyl orthosilicate matrix using single beam z-scan technique at 532 nm by Q-switched Nd:YAG laser. We have shown that mechanisms responsible for third-order optical nonlinearity of Ag nanocomposite film are reverse saturable absorption (RSA) and self-defocusing in the purlieu of surface plasmon resonance (SPR). Optical band-gap and width of SPR band of Ag nanocomposite film decrease with increasing silver concentration, which leads to enhancement of local electric field and hence third-order optical nonlinearity. Optical limiting, due to RSA has also been demonstrated at 532 nm.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Nonlinear characterization of a single-axis acoustic levitator

The nonlinear behavior of a 20.3 kHz single-axis acoustic levitator formed by a Langevin transducer with a concave radiating surface and a concave reflector is experimentally investigated. In this study, a laser Doppler vibrometer is applied to measure the nonlinear sound field in the air gap between the transducer and the reflector. Additionally, an electronic balance is used in the measurement of the acoustic radiation force on the reflector as a function of the distance between the transducer and the reflector. The experimental results show some effects that cannot be described by the linear acoustic theory, such as the jump phenomenon, harmonic generation, and the hysteresis effect. The influence of these nonlinear effects on the acoustic levitation of small particles is discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Fatigue damage evaluation of austenitic stainless steel using nonlinear ultrasonic waves in low cycle regime

The interrupted low cycle fatigue test of austenitic stainless steel was conducted and the dislocation structure and fatigue damage was evaluated subsequently by using both transmission electron microscope and nonlinear ultrasonic wave techniques. A “mountain shape” correlation between the nonlinear acoustic parameter and the fatigue life fraction was achieved. This was ascribed to the generation and evolution of planar dislocation structure and nonplanar dislocation structure such as veins, walls, and cells. The “mountain shape” correlation was interpreted successfully by the combined contribution of dislocation monopole and dipole with an internal-stress dependent term of acoustic nonlinearity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Nonlinear theory of classical cylindrical Richtmyer-Meshkov instability for arbitrary Atwood numbers

A nonlinear theory is developed to describe the cylindrical Richtmyer-Meshkov instability (RMI) of an impulsively accelerated interface between incompressible fluids, which is based on both a technique of Padé approximation and an approach of perturbation expansion directly on the perturbed interface rather than the unperturbed interface. When cylindrical effect vanishes (i.e., in the large initial radius of the interface), our explicit results reproduce those [Q. Zhang and S.-I. Sohn, Phys. Fluids 9, 1106 (1996)] related to the planar RMI. The present prediction in agreement with previous simulations [C. Matsuoka and K. Nishihara, Phys. Rev. E 73, 055304(R) (2006)] leads us to better understand the cylindrical RMI at arbitrary Atwood numbers for the whole nonlinear regime. The asymptotic growth rate of the cylindrical interface finger (bubble or spike) tends to its initial value or zero, depending upon mode number of the initial cylindrical interface and Atwood number. The explicit conditions, directly affecting asymptotic behavior of the cylindrical interface finger, are investigated in this paper. This theory allows a straightforward extension to other nonlinear problems related closely to an instable interface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Quantum corrections to nonlinear ion acoustic wave with Landau damping

Quantum corrections to nonlinear ion acoustic wave with Landau damping have been computed using Wigner equation approach. The dynamical equation governing the time development of nonlinear ion acoustic wave with semiclassical quantum corrections is shown to have the form of higher KdV equation which has higher order nonlinear terms coming from quantum corrections, with the usual classical and quantum corrected Landau damping integral terms. The conservation of total number of ions is shown from the evolution equation. The decay rate of KdV solitary wave amplitude due to the presence of Landau damping terms has been calculated assuming the Landau damping parameter α{sub 1}=√(m{sub e}/m{sub i}) to be of the same order of the quantum parameter Q=ℏ{sup 2}/(24m{sup 2}c{sub s}{sup 2}L{sup 2}). The amplitude is shown to decay very slowly with time as determined by the quantum factor Q.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Linear and nonlinear dust acoustic waves in an inhomogeneous magnetized dusty plasma with nonextensive electrons

The propagation of both linear and nonlinear dust acoustic waves (DAWs) in an inhomogeneous magnetized collisional and warm dusty plasma (DP) consisting of Boltzmann ions, nonextensive electrons, and inertial dust particles is investigated. The number density gradients of all DP components besides the inhomogeneities of electrostatic potential and the initial dust fluid velocity are taken into account. The linear dispersion relation and a nonlinear modified Zakharov-Kusnetsov (MZK) equation governing the propagation of the three-dimensional DAWs are derived. The analytical solution of the MZK reveals the creation of both compressive and rarefactive DAW solitons in the proposed model. It is found that the inhomogeneity dimension parameter and the electron nonextensive parameter affect significantly the nonlinear DAW's amplitude, width, and Mach number. The relations of our findings with some astrophysical situations have been given.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A quantum quasi-harmonic nonlinear oscillator with an isotonic term

The properties of a nonlinear oscillator with an additional term k{sub g}/x², characterizing the isotonic oscillator, are studied. The nonlinearity affects to both the kinetic term and the potential and combines two nonlinearities associated to two parameters, κ and k{sub g}, in such a way that for κ = 0 all the characteristics of the standard isotonic system are recovered. The first part is devoted to the classical system and the second part to the quantum system. This is a problem of quantization of a system with position-dependent mass of the form m(x) = 1/(1 − κx²), with a κ-dependent non-polynomial rational potential and with an additional isotonic term. The Schrödinger equation is exactly solved and the (κ, k{sub g})-dependent wave functions and bound state energies are explicitly obtained for both κ < 0 and κ > 0.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Dispersion of the linear and nonlinear optical susceptibilities of the CuAl(S{sub 1–x}Se{sub x})₂ mixed chaclcopyrite compounds

Based on the electronic band structure, we have calculated the dispersion of the linear and nonlinear optical susceptibilities for the mixed CuAl(S{sub 1–x}Se{sub x})₂ chaclcopyrite compounds with x=0.0, 0.25, 0.5, 0.75, and 1.0. Calculations are performed within the Perdew-Becke-Ernzerhof general gradient approximation. The investigated compounds possess a direct band gap of about 2.2 eV (CuAlS₂), 1.9 eV (CuAl(S₀.₇₅Se₀.₂₅)₂), 1.7 eV (CuAl(S₀.₅Se₀.₅)₂), 1.5 eV (CuAl(S₀.₂₅Se₀.₇₅)₂), and 1.4 eV (CuAlSe₂) which tuned to make them optically active for the optoelectronics and photovoltaic applications. These results confirm that substituting S by Se causes significant band gaps' reduction. The optical function's dispersion ε₂{sup xx}(ω) and ε₂{sup zz}(ω)/ε₂{sup xx}(ω), ε₂{sup yy}(ω), and ε₂{sup zz}(ω) was calculated and discussed in detail. To demonstrate the effect of substituting S by Se on the complex second-order nonlinear optical susceptibility tensors, we performed detailed calculations for the complex second-order nonlinear optical susceptibility tensors, which show that the neat parents compounds CuAlS₂ and CuAlSe₂ exhibit | χ₁₂₂²}(-2ω;ω;ω) | as the dominant component, while the mixed alloys exhibit | χ₁₁₁²(-2ω;ω;ω) | as the dominant component. The features of | χ₁₂₃²}(-2ω;ω;ω) | and | χ{sub 111}²}(-2ω;ω;ω) | spectra were analyzed on the basis of the absorptive part of the corresponding dielectric function ε₂(ω) as a function of both ω/2 and ω.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗