Large nonlinear optical properties of Fe2O3 nanoparticles

Nonlinear optical properties of Fe₂O₃ nanoparticles were investigated by the signal-beam Z-scan technique with Ar⁺ and Ne–He lasers. The largest reported effective nonlinear coefficient, n₂=−8.07×10⁻⁷ cm²/W, was obtained. It is demonstrated that the nonlinear optical response originals from quantum confinement effect.     

Nonlinear optical responses of Sudan IV doped liquid crystal by z-scan and moiré deflectometry techniques

The nonlinear optical properties of a nematic liquid crystal doped with an azo dye were investigated. The magnitude and the sign of the third-order nonlinear refractive index, n₂, were measured using both single-beam z-scan and moiré deflectometry techniques. The measurements were performed at 532 nm using a Nd:Yag CW laser. The positive sign showed that sample which was studied possess a self-focusing optical nonlinearity. Rather close agreement was found between the values for n₂ obtained by z-scan and by moiré deflectometry. The nonlinear refractive index was found to be in the order of 10^− 6 (cm²/W) and the nonlinear absorption coefficient to be β = 0.171 (cm/W).     

Electron impact ionization of atomic clusters in ultraintense laser fields

In this paper we report on inner ionization of Xe_n clusters (n = 55- 2171) in ultraintense Gaussian laser fields (peak intensity I = 10¹⁵- 10²⁰ Wcm^-2, pulse width τ= 25 fs, frequency 0.35 fs^-1). The cluster inner ionization process is induced by the barrier suppression ionization (BSI) mechanism and by electron impact ionization (EII), which occurs sequentially with the BSI. We address electron impact ionization of clusters, which pertains to inelastic reactive processes of the high-energy (100 eV–1 keV per electron) nanoplasma. We utilized experimental data for the energy dependence of the electron impact ionization cross-sections of Xe^j+ (j = 1-10) ions, which were fit by an empirical three-parameter Lotz-type equation, to explore EII in clusters by molecular dynamics simulations. Information was obtained on the yields and time-resolved dynamics of the EII levels (i.e., number n_imp of electrons per cluster atom) in the Xe_n clusters and their dependence on the laser intensity and cluster size. The relative long-time (t = 90 fs) yields for EII, n_imp/n_ii (where n_ii is the total inner ionization yield) are rather low and increase with decreasing the laser intensity. In the intensity range I = 10¹⁵-10¹⁶ Wcm^-2, n_imp/n_ii = 0.21 for n = 2171 and n_imp/n_ii = 0.09-0.14 for n = 459, while for I = 10¹⁸-10²⁰ Wcm^-2, n_imp/n_ii = 0.01-0.05. The difference Δn_imp between the EII yield at long time and at the termination of the laser pulse reflects on ionization dynamics by the nanoplasma when the laser pulse is switched off. For Xe₂₁₇₁ in the lower intensity domain, Δ n_imp = 0.9 at I = 10¹⁵ Wcm^-2 and Δn_imp = 0.4 at 10¹⁶ Wcm^-2, reflecting on EII by the persistent nanoplasma under “laser free” conditions, while in the higher intensity domain of I = 10¹⁷ - 10¹⁸ Wcm^-2, Δn_imp is negligibly small due to the depletion of the transient nanoplasma.     

Guided propagation in a step-index, multi-mode fiber: effect of index difference variation on allowable TM propagation constants

The effect of variation of core and cladding index difference, Δn=n_core−n_cladding, on allowable values for the guided mode transverse magnetic propagation constants within a step-index, multi-mode optical fiber is investigated. We use a iterative computational technique to calculate the propagation constants for modes inside and outside the core that satisfy the boundary conditions contained within the characteristic eigen-equation for the TM field components. Evidence of a strong dependence of the allowable propagation constants on changes of Δn is shown.     

Multiple Andreev reflections in diffusive SNS structures

We report new measurements on subgap energy structures originating from multiple Andreev reflections in mesoscopic SNS junctions. The junctions were fabricated in a planar geometry with high-transparency superconducting contacts of Al deposited on highly diffusive and surface δ -dopedn ^{+ +} -GaAs. For samples with a normal GaAs region of active length 0.3μ m, the Josephson effect with a maximal supercurrent I_c = 3μ A at T = 237 mK was observed. The subgap structure was observed as a series of local minima in the differential resistance at dc bias voltages V = ± 2Δ / (ne) with n = 1, 2, 4, i.e. only the even subgap positions. While at V = ± 2Δ / e(n = 1) only one dip is observed, then = 2 and the n = 4 subgap structures each consists of two separate dips in the differential resistance. The mutual spacing of these two dips is independent of temperature, and the mutual spacing of the n = 4 dips is half the spacing of the n = 2 dips. The voltage bias positions of the subgap differential resistance minima coincide with the maxima in the oscillation amplitude when a magnetic field is applied in an interferometer configuration, where one of the superconducting electrodes has been replaced by a flux-sensitive open loop.     

Neutrino mixing and see-saw mechanism

Models of neutrino masses are discussed capable of explaining in a natural way the maximal mixing between ν_μ and ν_τ observed by the Super-Kamiokande Collaboration. For three generations of leptons two classes of such models are found implying: a) Δm₂₃²Δm₁₂²≈Δm₁₃² and a small mixing between ν_e and the other two neutrinos, b) Δm₁₂²Δm₁₃²≈Δm₂₃² and a nearly maximal mixing for solar neutrino oscillations in vacuum.     

Contributions to the Gaussian Line Broadening of the Proxyl Spin Probe EPR Spectrum Due to Magnetic-Field Modulation and Unresolved Proton Hyperfine Structure

A simple expression is derived to compute the total Gaussian linewidth of a Voigt line that is broadened by sinusoidal magnetic-field modulation as follows: ΔH^G_pp(H_m)²= ΔH^G_pp(0)²+ κ²H²_m, where ΔH^G_pp(H_m) is the Gaussian linewidth observed with an modulation amplitudeH_m/2 and ΔH^G_pp(0) is the Gaussian linewidth in the limit of zero modulation. The field modulation contributes an additional Gaussian broadening of κH_m, where κ is a constant, which adds in quadrature to ΔH^G_pp(0) to give the total Gaussian linewidth. Denoting the overall linewidth of the Voigt line in the absence of modulation broadening by ΔH⁰_pp(0), it is shown, both by analytical means and by spectral simulation, that the constant κ is equal to 1/2 in the limit ofH_m ΔH⁰_pp(0); however, using values ofH_mas large as ΔH⁰_pp(0) leads to only minor departures from κ = 1/2. The formulation is valid both for Lorentzian and Voigt lines and is tested for 2,2,5,5-tetramethylpyrrolidin-1-oxyl-3-carboxylic acid (3-carboxy proxyl) in CCl₄and in aqueous buffer. This spin probe was studied because the proxyl group is the only major spin-probe moiety whose Gaussian linewidth had not been characterized in the literature. For 3-carboxy proxyl, it is found that ΔH^G_pp(0) = 1.04 ± 0.01 G independent of solvent polarity. Precision values of the¹⁴N hyperfine coupling constant for 3-carboxy proxyl at 9.5°C are as follows: 14.128 ± 0.001 G in CCl₄and 16.230 ± 0.002 G in aqueous buffer. The temperature dependence of ΔH^G_pp(0) and the¹⁴N hyperfine coupling constant are reported as empirical equations. Results of the present work taken together with previously published data permits accurate correction for the effects of inhomogeneous broadening due to unresolved hyperfine structure and modulation broadening for the majority of spin probes in common use.     

Vicinal Fluorine–Proton Coupling Constants: II. Individual Substituent Effects

The angular dependence and the effect of individual substituents upon the NMR vicinal fluorine–proton couplings3JFHhave been studied using data sets of experimental and calculated couplings. Coupling constants for a series of fluoroethane derivatives, CHXF–CH3and CH2F–CH2X(X= CH3, NH2, OH, and F), were calculated by means of the SCFab initioand semiempirical INDO/FPT methods. The calculated couplings reproduce correctly the main experimental trends in spite of the limitation in the calculation because of lack of electronic correlation and the use of medium size basis set. The individual substituent effects ΔKXiniare described by quadratic expressions on the relative electronegativities of substituents ΔχXi(ΔKXini=k0ni+kniΔχXi+ kniiΔχ2Xi). A selected data set of 58 experimental couplings, ranging from 1.9 to 44.4 Hz, has been collected from the literature. An extended Karplus equation with 16 coefficients that includes the electronegativity substituent effects has been derived from the experimental data set with a root-mean-square deviation of 1.2 Hz.     

Families of commuting transfer matrices and integrable models with disorder

A family of commuting transfer matrices is shown to be associated to each symmetry transformation of a given Yang-Baxter algebra. This applies in lattices models and field theory.The Yang-Baxter algebra remains unchanged when an arbitrary parameter μ_l is associated to each lattice site. We generate in this way integrable one-dimensional hamiltonians with long-range couplings and disorder given by the <{;μ₁<};. These operators are lattice versions of the non-local charges in sigma models. As a simple example we get a Dzialozhinski-Moriya interaction with an arbitrary coupling per site from the six-vertex model. A similar model with a disordered magnetic field follows too. Their exact solution by an algebraic Bethe ansatz is presented. We derive the excitations spectrum in terms of the density of parameters (μ).As another application, the total spin S² is computed for a XXZ Heisenberg chain (μ_l ≡ 0) as a function of the anisotropy Δ (− ∞ < Δ < + ∞).     

Novel optical film sensor design based on p-polarized reflectance

A new scheme of optical film sensor is presented. The sensor is based on p-polarized reflectance, consisting of a sensing coated substrate, is easily optimized for maximum sensitivity in different applications. The resolutions of refractive index n_f, extinction coefficient k_f and thickness h_f of the sensitive films are predicted to be 10⁻⁷, 10⁻⁵ and 10⁻³ nm, respectively. Experimentally, we selected the sol–gel derived SnO₂ films as gas-sensitive films and conducted preliminary gas-sensing test. The results indicate that novel optical film sensor scheme has higher sensitivity, and the detection sensitivity is available to 10⁻¹ ppm on the condition of optimum optical parameters and incident angle.     

The far-infrared spectrum and spectroscopic parameters of PH3 in the ground state

The far-infrared spectrum of phosphine, PH₃, was recorded in the region between 30 and 200 cm⁻¹ at a resolution of 0.002 cm⁻¹. ΔJ = +1, ΔK = 0 rotational transitions in the ground state were measured and assigned up to J″ = 22 and K = 19. These transitions were analyzed together with the presently available microwave and submillimeter-wave data on the basis of different formulations of the rotational Hamiltonian, which included Δk = ±3 and/or Δk = ±6 interaction terms. An upper limit for the constant of the inversion splitting was obtained by fitting the same transitions to an appropriate inversion-rotational Hamiltonian. Rotational transitions in the v₂ = 1 and v₄ = 1 vibrational states were also observed.     

New observation of the , 1Δg, and 2Πg states and molecular constants with all Li2, Li2, and LiLi data

This paper reports our new observation of the , 1³Δ_g (v = 2–4), and 2³Π_g (v = 2–8) states of ⁶Li⁷Li by continuous wave perturbation facilitated optical–optical double resonance spectroscopy. Combining our new experimental term values of ⁶Li⁷Li with the available experimental data of ⁶Li₂ and ⁷Li₂, molecular constants and potential energy curves by Rydberg–Klein–Rees and direct-potential-fit techniques have been determined. Born-Oppenheimer breakdown parameters of the Li₂ 1³Δ_g and 2³Π_g states are calculated.     

Time Correlations in Fluid Transport Obtained by Sequential Rephasing Gradient Pulses

We present a basic experiment by which the evolution of the displacement probability density (propagator) of static or flowing fluid inNsuccessive time intervals is obtained by single labeling, coupled with multiple rephasing events during the course of a pulsed field-gradient sequence. We term this type of sequence SERPENT: SEquential Rephasing by Pulsed field-gradients Encoding N Time-intervals. Realizations of the SERPENT experiment for the caseN= 2 which include spin echo, stimulated echo, and Carr–Purcell pulse sequences are suggested. They have in common a spatial spin-labeling of the initial magnetization by a gradient of area q₀, followed by successive rephasing via gradients q₁and q₂at timest= Δ₁andt= Δ₂, respectively, where q₀+ q₁+ q₂= 0. A two-dimensional Fourier transform with respect to q₁and q₂gives directly the joint probability densityW₂(R₁, Δ₁; R₂, Δ₂) for displacements R₁and R₂in times Δ₁and Δ₂, respectively. q₁and q₂may be in arbitrary directions. Assuming R₁R₂, the correlation coefficient ρ_R1,R2then reflects the time-history of the fluctuating velocities. The behavior of the cross moment R₁(Δ₁) · R₂(Δ₂) can be obtained from either a full two-dimensional or a set of one-dimensional SERPENT measurements. Experimental results are presented for water flowing through a bed of packed glass beads. While Δ₁is appropriately chosen to sample the short-time velocity field within the system, increasing Δ₂clearly shows the loss of correlation when the average fluid element displacement exceeds the bead diameter.     

Chiral approach to nuclear matter: role of two-pion exchange with virtual delta-isobar excitation

We extend a recent three-loop calculation of nuclear matter by including the effects from two-pion exchange with single and double virtual Δ(1232)-isobar excitation. Regularization dependent short-range contributions from pion-loops are encoded in a few NN-contact coupling constants. The empirical saturation point of isospin-symmetric nuclear matter, , ρ₀=0.16 fm⁻³, can be well reproduced by adjusting the strength of a two-body term linear in density (and tuning an emerging three-body term quadratic in density). The nuclear matter compressibility comes out as K=304 MeV. The real single-particle potential U(p,k_f0) is substantially improved by the inclusion of the chiral πNΔ-dynamics: it grows now monotonically with the nucleon momentum p. The effective nucleon mass at the Fermi surface takes on a realistic value of M^*(k_f0)=0.88M. As a consequence of these features, the critical temperature of the liquid-gas phase transition gets lowered to the value T_c15 MeV. In this work we continue the complex-valued single-particle potential U(p,k_f)+iW(p,k_f) into the region above the Fermi surface p>k_f. The effects of 2π-exchange with virtual Δ-excitation on the nuclear energy density functional are also investigated. The effective nucleon mass associated with the kinetic energy density is . Furthermore, we find that the isospin properties of nuclear matter get significantly improved by including the chiral πNΔ-dynamics. Instead of bending downward above ρ₀ as in previous calculations, the energy per particle of pure neutron matter and the asymmetry energy A(k_f) now grow monotonically with density. In the density regime ρ=2ρ_n<0.2 fm⁻³ relevant for conventional nuclear physics our results agree well with sophisticated many-body calculations and (semi)-empirical values.     

Dispersive optical constants of a-Se100−xSbx films

Thin films of amorphous Se_100−xSb_x (x=5,10 and 20 at%) system are deposited on a silicon substrate at room temperature (300 K) by thermal evaporation technique. The optical constant such as refractive index (n) has been determined by a method based on the envelope curves of the optical transmission spectrum at normal incidence by a Swanpoel method. The oscillator energy (E_o), dispersion energy (E_d) and other parameters have been determined by the Wemple–DiDomenico method. The absorption coefficient (α) has been determined from the reflectivity and transmitivity spectrum in the range 300–2500 nm. The optical-absorption data indicate that the absorption mechanism is a non-direct transition. We found that the optical band gap, E_g^opt, decreases from 1.66±0.01 to 1.35±0.01 eV with increase Sb content.     

Numerical renormalization group studies of SU(4) Kondo effect in quantum dots

We theoretically study an enhancement of the Kondo effect in quantum dots with two orbitals and spin . The Kondo temperature and conductance are evaluated as functions of energy difference Δ between the orbitals, using the numerical renormalization group method. The Kondo temperature is maximal around the degeneracy point (Δ=0) and decreases with increasing |Δ| following a power law, T_K(Δ)=T_K(0)(T_K(0)/|Δ|)^γ, which is consistent with the scaling analysis. The conductance at T=0 is almost constant 2e²/h. Both the orbitals contribute to the conductance around Δ=0, whereas the current through the upper orbital is negligibly small when |Δ|T_K(0). These are characteristics of SU(4) Kondo effect.     

Electronic structure and infrared spectrum of a WnC0＇± （n= 1-6） cluster

W_nC^0,± (n=1-6) clusters are investigated by using the density functional theory (DFT) at the B3LYP/LANL2DZ level. We find that the neutral, anionic and cationic ground state structures are similar within the same size, and constituted by substituting a C atom for one W atom in the structures of W_n+1 clusters. The natural bond orbital (NBO) charge analyses indicate that the direction of electron transfer is from the W atom to the 2p orbital of the C atom. In addition, the calculated infrared spectra of the W_nC^0,± (n=2-6) clusters manifest that the vibrational frequencies of neutral, anionic and cationic clusters are similar in a range of 80 cm^-1-864 cm^-1. The high frequency, strong peak modes are found to be an almost stretched deformation of the carbide atom. Finally, the polarizabilities of W_nC^0,± (n=1-6) clusters are also discussed.     

Sulfur dioxide: Rotational constants and asymmetric structure of the state

Eight bands of the 2350 Å system of sulfur dioxide have been rotationally analyzed as A-type transitions of a prolate asymmetric rotor, confirming that the electronic transition is ¹B₂ ← ¹A₁[2b₁(π^*) ← 1a₂(π)]. The electronic energy and rotational constants of the 0-0 band are, in cm⁻¹: These constants correspond to the average structure r₀ = 1.560 Å and θ₀ = 104.3°. However, the vibrational structure can only be satisfactorily accounted for on the hypothesis of a double-minimum potential in the antisymmetrical stretching coordinate Q₃, the energies of the fundamental levels in the three modes of the B₂ state being: (100), 960 cm⁻¹; (010), 377 cm⁻¹; and (001), 220 cm⁻¹ The (001) level is not observed in the spectrum but can be calculated from the distortion constants and inertial defect of the rotational analysis: the level (002) = 561 cm⁻¹, obtained directly from the vibrational structure, establishes that there is strong, positive anharmonicity in the first three levels of this vibration, as required by the assumption of a double-minimum potential function. Preliminary values are reported for the barrier to the symmetrical configuration, V/hc 100 cm⁻¹, and for the difference in bond distances in the equilibrium configuration, Δr0.12 Å. Coon and his co-workers have previously considered the possible asymmetry of this state but the Q₃ inversion barrier obtained by them, 656 cm⁻¹, is much higher than in the present work, and reasons for this are discussed.     

Excess molar volumes, viscosities, and refractive indices for binary and ternary mixtures of {cyclohexanone (1) + N,N-dimethylacetamide (2) + N,N-diethylethanolamine (3)} at (298.15, 308.15, and 318.15) K

Densities ρ, viscosities η, and refractive indices n_D, of the binary and ternary mixtures formed by cyclohexanone + N,N-dimethylacetamide + N,N-diethylethanolamine were measured at (298.15, 308.15, and 318.15) K for the liquid region and at ambient pressure for the whole composition ranges. The excess molar volumes V_m^E, viscosity deviations Δη, and refractive index deviations Δn_D, were calculated from experimental densities and refractive indices. The excess molar volumes are positive over the mole fraction range for binary mixtures of cyclohexanone(1) + N,N-dimethylacetamide (2) and N,N-dimethylactamide (2) + N,N-diethylethanolamine (3) and increase with increasing temperatures from (298.15 to 318.15) K. The excess molar volumes of cyclohexanone (1) + N,N-diethylethanolamine (3) are S-shaped dependence on composition with negative values in the N,N-diethylethanolamine rich-region and positive values at the opposite extreme and increase with increasing temperatures from (298.15 to 318.15) K. The excess molar volumes are positive over the whole mole fraction ranges for the ternary mixtures at all temperatures. Viscosity deviations are negative over the mole fraction range for all binary and ternary mixtures and decrease with increasing temperatures from (298.15 to 318.15) K. Refractive index deviations are negative over the mole fraction range for all binary and ternary mixtures and increase with increasing temperatures from (298.15 to 318.15) K. The experimental data of constitute were correlated as a function of the mole fraction by using the Redlich–Kister equation for binary and , Cibulka, Jasinski and Malanowski , Singe et al., Pintos et al., Calvo et al., Kohler, and Jacob–Fitzner for ternary mixture, respectively. McAllister^'s three body, Hind, and Nissan–Grunberg models were used for correlating the kinematic and dynamic viscosity of binary mixtures. The experimental data of the constitute binaries are analyzed to discuss the nature and strength of intermolecular interactions in these mixtures.     

First-principles identification of two- and four-membered-ring hybrid structures of silica nanorings

We performed first-principles calculations to study the energetics, IR spectra, and electronic structures of silica nanorings (NR) consisting of two- and four-membered ring (2-4MR) units. A comparison study of other silica clusters, such as nanochains (NC) and nanorings formed by two-membered rings (2MRs) was made. The results show that for small-size (SiO₂)_n clusters with n<24, the nanochains composed of 2-4MRs (2-4MR-NCs) are more stable than other kinds of NRs and NCs. When n>24 the 2-4MR-NRs structures become energetically favorable. 2-4MR-NRs have the narrowest HOMO–LUMO gaps which increase with increasing cluster size, distinctive IR spectra characterized by several peaks at the 1000–1150 cm⁻¹ region.