Optical properties of binary composite materials with two nonlinear components

Abstract

A new formulation is presented for the calculation of effective dielectric magnitudes of two-component composites in which both components (the host matrix particles and the embedded particles) exhibit nonlinear behaviour of the Kerr type. It is predicted that, under certain conditions, two nonlinear component composites can exhibit optical bistable behaviour as a function of the shape and concentration of the embedded particles, the dielectric contants of the components, the intensity of the external electric field (power density) and the intrinsic third-order nonlinear optical susceptibilities χ⁽³⁾ _p and χ⁽³⁾ _m of the nonlinear components. It is also deduced that, as the power density increases, the effective third-order nonlinear optical susceptibility χ⁽³⁾ of the composite exhibits a clear transition from values close to χ⁽³⁾ _p (low power density) to χ⁽³⁾ _m (high power density). Therefore, it is shown that the optical response of binary composites dramatically changes at moderate and high power densities. A comparison is performed between the optical response of a real two nonlinear component composite and that of a composite with a single nonlinear component.     

On the Structure of the Superfluid State and Quasiparticle Spectrum in a Bose Liquid with a Suppressed Bose–Einstein Condensate

A self-consistent model of the superfluid (SF) state of a Bose liquid with strong interaction between bosons and a weak single-particle Bose–Einstein condensate (BEC) is considered. The ratio of the BEC density n ₀ to the total particle density n of the Bose liquid is used as a small parameter of the model, n ₀/n?1, unlike in the Bogolyubov theory of a quasi-ideal Bose gas, in which the small parameter is the ratio of the number of supracondensate excitations to the number of particles in an intensive BEC, (n?n ₀)/n ₀?1. A closed system of nonlinear integral equations for the normal ~Σ₁₁(p, ω) and anomalous ~Σ₁₂(p, ω) self-energy parts is obtained with account for terms of first order in the BEC density. A renormalized perturbation theory is used, which is built on combined hydrodynamic (at p→0) and field (at p≠0) variables with analytic functions ~Σ _ij (p, ε) at pε0 and ε→0 and a nonzero SF order parameter ~Σ₁₂(0, 0)≠0, proportional to the density ρ _s of the SF component. Various pair interaction potentials U(r) with inflection points in the radial dependence and with an oscillating sign-changing momentum dependence of the Fourier component V(p) are considered. Collective many-body effects of renormalization (“screening”) of the initial interaction, which are described by the bosonic polarization operator Π(p, ω), lead to a suppression of the repulsion [V(p)<0] and an enhancement of the effective attraction [V(p)<0] in the respective domains of nonzero momentum transfer, due to the negative sign of the real part of Π(p, ω) on the “mass shell” ω=E(p). In the framework of the “soft spheres” model with the single fitting parameter—the value of the repulsion potential at r=0—the quasiparticle spectrum E(p) is calculated, which is in good accordance with the experimental spectrum E _exp(p) of elementary excitations in superfluid ⁴He. It is shown that the roton minimum in the quasiparticle spectrum is directly associated with the first negative minimum of the Fourier component of the renormalized (“screened”) potential of pair interaction between bosons.     

Breathable Nanowood Biofilms as Guiding Layer for Green On‐Skin Electronics

Thin‐film electronics are urged to be directly laminated onto human skin for reliable, sensitive biosensing together with feedback transdermal therapy, their self‐power supply using the thermoelectric and moisture‐induced‐electric effects also has gained great attention (skin and on‐skin electronics (On‐skinE) themselves are energy storehouses). However, “thin‐film” On‐skinE 1) cannot install “bulky” heatsinks or sweat transport channels, but the output power of thermoelectric generator and moisture‐induced‐electric generator relies on the temperature difference (?T ) across generator and the ambient humidity (AH), respectively; 2) lack a routing and accumulation of sweat for biosensing, lack targeted delivery of drugs for precise transdermal therapy; and 3) need insulation between the heat‐generating unit and heat‐sensitive unit. Here, two breathable nanowood biofilms are demonstrated, which can help insulate between units and guide the heat and sweat to another in‐plane direction. The transparent biofilms achieve record‐high transport_///transport_⊥ (//: along cellulose nanofiber alignment direction, ⊥: perpendicular direction) of heat (925%) and sweat (338%), winning applications emphasizing on ?T/AH‐dependent output power and “reliable” biosensing. The porous biofilms are competent in applications where “sensitive” biosensing (transporting_// sweat up to 11.25 mm s^?1 at the 1st second), “insulating” between units, and “targeted” delivery of saline‐soluble drugs are of uppermost priority.     

A strategy based on the strain-to-kinetic energy ratio to ensure stability and convergence in topology optimization of globally resonating one-material structures

The authors propose a new formulation of SIMP-based topology optimization problems aiming to obtain resonating one-material structures through a stable maximization process. The new formulation is capable of achieving globally resonant lightly damped “0-1” structures for frequencies close to those of interest. The proposed strategy successfully deals with known issues like design “degeneration” and instability of the gradient-based optimization process around the resonance frequency (which is a local maximum when maximizing vibration responses) at which harmonic excitation forces shall be applied. In this work, the authors use the concept of complex input power to overcome the mentioned issues. It is proposed a topology optimization procedure where a weighted sum between the active input power (real part of the complex input power) and the static compliance is minimized with a constraint on the reactive input power (imaginary part of the complex input power), which is converted to a ratio between the time-averaged potential and kinetic energies of the system named quotient R. By this way, it is possible to ensure viability to the procedure by preventing the resonance frequency from reaching exactly the excitation frequency throughout the process, which otherwise causes difficulties on convergence. The process achieves resonance frequencies very close to given values of interest by keeping the “side” of R<1 or R>1. Several examples are presented to illustrate the potential of the proposed method.     

Large-Area YBa2Cu3O7 − x Films on Sapphire with Excellent Microwave Power Handling Capability

Crack-free thick YBa₂Cu₃O_{7 ? x} films are prepared on CeO₂ buffered r-cut sapphire (2 inch in diameter) with thickness up to 700 nm, smooth surfaces (“peak-to-valley” roughness <10 nm), high critical currents (J _C > 2 MA/cm² at 77 K and 0 T), and low microwave surface resistances (R _s(77K) ?.4mω and R _s(4.2K) ?.110μω at 19.15GHz) comparable to the best values reported in the literature for YBCO films on structurally better matched substrates. These thick YBCO films were able to handle high microwave power corresponding to magnetic field amplitudes (B _HF) up to 54, 37, and 17.4 mT at 4.2, 50, and 77 K, respectively, which for the lower temperatures were limited by the available power of the 25-W HF amplifier. The high-power performance, which to our knowledge belongs to the best reported so far for unpatterned YBa₂Cu₃O_{7 ? x} films, was achieved without any degradation of the samples despite frequent thermal cycling.     

Electroreflectance spectra of thin silicon films

Electroreflectance spectra for thin silicon films have been investigated in the photon energy region 2.8–5.0 eV. The critical point energy E₁(E′'₀) and the broadening parameter Γ were determined for unexposed and ion-bombarded surfaces. Definite correlation between Γ^-1 and the Hall mobility was found. It is concluded that the variations in E₁(E_'0) for the films are caused by the emergence of density “tails” and the existence of inward mechanical microtensions.     

Thermonuclear fusion neutrons under “Currentless plasmas” in Heliotron E

Thermonuclear fusion neutron emissions of up to 3 × 10⁹ neutrons/s have been observed in Heliotron E deuterium plasmas. “Currentless plasmas” were produced by electron cyclotron resonance (53 GHz, 150 kW) and further heated by hydrogen neutral beam injection (2.2 MW, H⁰→D⁺). It is found that all observed neutron emissions have thermonuclear origin due to the absence of hard X-ray background. Agreement between neutron and charge exchange ion temperature measurements (500 eV < T_i(0) × 900 eV) have been found at intermediate densities $\text{(1.5 ×}\text{n}{}_{\mathrm{<mtext>e</mtext>}}\text{× 3 × 10}{}^{13}\text{cm}{}^{\mathrm{?3}}\text{)}$. The neutrons reported in this paper are the first observations of pure thermonuclear fusion neutrons in a helical heliotron plasma confinement device.     

Free vibrations of a piezoelectric layer of hexagonal (6mm) class

An asymptotic method due to “Achenbach” is used to analyze the free vibrations of a piezoelectric layer of hexagonal (6 mm) class. In this method, the displacement components, the electric potential and the frequency are expressed as power series of the dimensionless wavenumber ? = 27π × Layer Thickness/Wavelength. Substituting the expansions of field variables and the frequency in the field equations of piezoelectricity and in the boundary conditions, a system of coupled, second order, inhomogeneous, ordinary differential equations with thickness variable as the independent variable is obtained by collecting the terms of same order ^?n. Integration of such systems of differential equations yields the various terms in the series expansions for the field variables and the frequency, for all modes and in the whole range of frequencies, in a range of the dimensionless wavenumber $\text{0 < ? < ?}{}^1\text{< 1}$ where $\text{?}{}^1$ increases as more terms are retained in the expansions. The frequency coefficients reduce to the corresponding ones in the elastic case as a limit. The exact frequency equation in the case of plane strain is obtained and analyzed numerically. The results thus obtained are compared with those obtained in the asymptotic method. The results fairly agree upto three decimal places.     

Studying the high-field electron conduction of tetrahedral amorphous carbon thin films by conducting atomic force microscopy

The high-field electron conduction of tetrahedral amorphous carbon (ta-C) thin films substrate has been studied using a conducting atomic force microscope (C-AFM). The ta-C thin films with a high concentration of sp³ bonding (80–90%) were deposited on Si by field arc deposition (FAD). The high-field “conductance” and surface morphology were mapped simultaneously. At low bias, the “conductance” exhibits inhomogeneities on a large scale, presumably due to thickness variations or interface defects. However, at high bias, the small difference in “conductance” due to thickness variations or interface defects was buried by the high intrinsic “conductivity.” It has also been shown that high field causes electric breakdown in these films by converting sp³ bonding to sp² at high electric field.     

Nanosecond electric explosion of thin aluminum films

Pulsed electrodynamic breakage of thin (∼20-nm-thick) aluminum films deposited onto polymer substrates have been experimentally studied. The character of film fracture depends on the level of supplied electric energy W. For 3.5 kJ/g < W < 4.3 kJ/g, discontinuities (striations) are formed in the transverse direction relative to the applied electric field. At high current densities on a level of ∼(1–3) × 10¹² A/m² and explosion times within 50–300 ns, the integral of action to explosion varies within (0.79–1.08) × 10¹⁷ A s/m² depending on the rate of energy supply and differs from published data for relatively massive conductors.     

Laser-induced transformation of a-C:H thin films

In this work, we report the laser irradiation effects on the properties of various types of amorphous hydrogenated carbon (a-C:H) films. The influence of the initial carbon film (hydrogen concentration, sp³/sp² ratio, and sp² clustering) is studied. The results show that a loss of hydrogen and an increase of the sp² phase are the main processes in the laser power range between 1.8 and 5 MW/cm². Only these processes are stronger for “more polymer-like” and “graphite-like” films than for “more diamond-like” films.     

A New Interpretation of Gas Viscosity for Flow through Micro-Capillaries and Pores

The Hagen–Poiseuille equation for gas flow had never been derived theoretically; it is rather a simple analogy of the same for liquid flow, and “gas viscosity” is a measure for overall resistance to flow. In this work, experimental flow data for different gases through capillaries and porous media, reported in literature by different groups, including those measured and treated by Knudsen are treated with Hagen–Poiseuille equation, but taking “gas viscosity” as an adjustable parameter. It is found that, at constant temperature, there exists an unambiguous relation between the viscosity (µ) of a given gas, and the product of average pressure (P_av) and capillary diameter (D). In addition, for P_av*D < 0.01, a universal linear relation exists between µ/M^0.5 (where M is molecular mass) for different gases and the parameter P_av*D. The new interpretation of gas viscosity avoids the differentiation of regimes into “Knudsen” and “viscous” flow as it is frequently done in literature. The concept can be applied to obtain a reliable data base for gas viscosities in different fields of applications, for example in microfluidic systems or the analysis of pore size distributions of filters and membranes by gas flow porometry.     

Time of flight of carriers in simple aromatic hydro-carbon layers I: Theory

It has been found that the drift velocity of carriers in polycrystalline layers of simple aromatic hydrocarbons increases proportionally to the electric field and saturates at a field of 2×10⁶Vm^?>1. In addition it has been inferred that the predominant conduction mechanism in polycrystalline simple aromatic hydro-carbon layers is a hopping process between localized states within the “impurity” band at the Fermi level. A simple model to explain the phenomenon was put forward earlier. In this paper the problem is discussed more exactly, using the assumption that so-called “difficult” jumps of carriers play a significant role in the transport of carriers in polycrystalline simple aromatic hydrocarbon layers.     

Comportement en courant alternatif de structures en couches minces AlSiO/B2O3Au

A.c. measurements were made on ten thin film samples AlSiO/B₂O₃Au. These samples were classified as “formable” or “non-formable” according to their d.c. current behaviour. The electronic emissions of these samples were also different in each case. We studied the variations with frequency of the real and imaginary parts of the dielectric susceptibilities of all the samples for different temperatures. For frequencies from a few hertz to 1 kHz we obtained the following relation for all the samples: χ′(ω) ∝ χ″(ω) ∝ ω^s?1 with s ≈ 0.27The main difference appears only in the low frequency range, where χ″ shows a maximum loss for the non-formable samples. It is possible that for the formable samples this loss peak is concealed by the d.c. current which predominates in these samples at low frequencies.     

Piezoelectric components wirelessly driven by dipole antenna-like electric field generator

A new technique of transmitting electric energy wirelessly to piezoelectric components by using a dipole antenna-like electric field generator is explored. Two square size brass plate-shaped live and ground electrodes are used to form a dipole antenna-like electric field generator. When the dipole antenna-like electric field generator in electric resonance with an inductor, a maximum output power of 2.72 mW and an energy conversion efficiency of 0.0174% have been achieved wirelessly by the piezoelectric plate area of 40 mm² operating in the thickness vibration mode, placed at the center 4 mm away from the antenna plane with an optimum electrical load of 1365 Ω, resonant frequency of 782 kHz, 1 cm electrodes separation, 2500 cm² electrode area of dipole antenna-like structure, and input ac source power of 15.58 W applied to the series of dipole antenna-like structure and inductor. The theoretically calculated results have been validated by the experimental studies. It is seen that at the resonance frequency and optimum electrical load, the output power of the wirelessly driven piezoelectric component decreases with the size of piezoelectric component, distance of piezoelectric component from the electrode of antenna plane, but increases with the antenna electrode area.     

Thermodynamic properties of TeO2-ZnO glasses in the range 0–650 K

The heat capacity C _p ⁰ of (TeO₂)_n(ZnO)_{1 ? n} (n = 0.65, 0.70, 0.80) tellurite glasses has been determined by precision adiabatic (6–350 K) and dynamic scanning (320–650 K) calorimetry. The thermodynamic characteristics of their devitrification and glassy state have been determined. The experimental data have been used to calculate the standard thermodynamic functions of samples in the glassy and “supercooled liquid” states (0–650 K): heat capacity C _p ⁰ (T), enthalpy H ⁰(T) ? H ⁰(0), entropy S ⁰(T) ? S ⁰(0), and Gibbs function G ⁰(T) ? H ⁰(0). Multifractal processing of the low-temperature heat capacity data has been used to assess the character of structural heterodynamicity of the tellurite glasses. The heat capacity of the glasses has been analyzed in comparison with that of their constituent oxides. The composition dependences of the glass transition temperature, crystallization onset temperature, and thermodynamic functions at 298.15 and 600 K have been obtained.     

Momentum transfer on power law stretching plate with free stream pressure gradient

The similarity solution of laminar boundary layer driven by the stretching surface boundary and pressure gradient, each proportional to the same power law of the downstream coordinate, based on composite reference velocity (sum of the velocities of stretching boundary and free stream) has been formulated by single set of equations, containing two parameters: β measuring the stretch rate of the moving boundary, and ? the ratio of free stream velocity to composite reference velocity. The closed form exact and asymptotic solutions in special cases, approximate integral solution and general numerical solutions have been obtained. For β>0 and 0???1 solutions are unique. For β<0 solutions are dual for 0<?<?₀(β), unique solution for ?=0 and ?=?₀(β) and no solution exists ?>?₀(β).     

Low power CW optical limiting properties of bis(2-aminopyridinium)-succinate-succinic acid (2APS) single crystal

The increase in the usage of low power CW lasers in various applications needs for the design of optical limiters with low thresholds. The optical limiting properties and nonlinear refractive index (n₂ = −2.4189 × 10⁻⁸ cm²/W) of transparent organic crystal bis(2-aminopyridinium)-succinate-succinic acid (2APS) single crystal using continuous wave He-Ne laser excitation following Z-scan method have been evaluated. The sample exhibited negative (defocusing) nonlinearity. This thermally induced defocusing nature of 2APS crystal can be used to design the low power optical limiters. As the origin for this nonlinearity is thermal, a complete thermal transport properties such as thermal diffusivity (α_s = 5.97 ± 0.03 × 10⁻³ cm²/s), thermal effusivity (e_s = 1.94 ± 0.02 × 10⁻² J/cm²-K-s^1/2), thermal conductivity (k_s = (4. 66 ± 0.04) × 10⁻³ W/cm-K)) and specific heat capacity (C_ps = (5.61 ± 0.05) × 10⁻¹ J/g-K) of the material were studied following the photopyro electric (PPE) technique.     

Beryllium neutron activation detector for pulsed DD fusion sources

A compact fast neutron detector based on beryllium activation has been developed to perform accurate neutron fluence measurements on pulsed DD fusion sources. It is especially well suited to moderate repetition-rate (<0.2 Hz) devices, such as the plasma focus or Z-pinch. The detector comprises a beryllium metal sheet sandwiched between two large-area xenon-filled proportional counters. A methodology for calculating the absolute response function of the detector using a “first principles” approach is described. This calibration methodology is based on the ⁹Be(n,α)⁶He cross-section, energy calibration of the proportional counters, and numerical simulations of neutron interactions and beta-particle paths using MCNP5. The response function R(E_n) is determined over the neutron energy range 2-4 MeV. The count rate capability of the detector has been studied and the corrections required for high neutron fluence measurements are discussed. For pulsed DD neutron fluencies >3×10⁴ cm⁻², the statistical uncertainty in the fluence measurement is better than 1%. A small plasma focus device has been employed as a pulsed neutron source to test two of these new detectors, and their responses are found to be practically identical. Also the level of interfering activation is found to be sufficiently low as to be negligible.