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1.
An intense ultraviolet picosecond light pulse at ωS = 2γP ? ωL is generated in water by noncollinear phase matched nonresonant four photon frequency mixing of two input picosecond light pulses at frequencies ν~P = 18 960 cm-1 and ν~L = 9480 cm-1. An energy conversion of up to WS/WL = 0.07 was achieved. The nonlinear susceptibility components were determined to be χ(3)yyyy(?ωS; ωP, ωP, ? ωL) = 7.5 × 10-34 Cm/V3 and χ(3)yxxy(?ωS; ωP, ωP, ?ωL) = 2.4 × 10-34 Cm/V3. 相似文献
2.
The paper presents the first report on χ(2) polarization induced in molecular glass of conjugated compound by all-optical poling. Transparent thin film of molecular glass of 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (BTAPVB) was prepared using a spin-cast technique. Dipolar as well as octupolar components in BTAPVB contributed to the formation of photoinduced χ(2) polarization. Growth rate of χ(2) polarization has good linear relation with Eω4E2ω, which suggested that the simultaneous processes of two-photon (ω + 2ω) and three-photon (ω + ω + ω) excitation on the same electronic level contributed to the formation of photoinduced χ(2) polarization. 相似文献
3.
We present a theory for the electron-temperature dependence T el of optical second harmonic generation (SHG). Such an analysis is required to study the dynamics of metallic systems with many hot electrons not at equilibrium with the lattice. Using a tight-binding theory for the nonlinear susceptibility χ (2)(ω,T e1) and the Fresnel coefficients we present results for the SHG intensity I (2)(ω,T e1) and its dependence on T el for Cu. Note, χ (2)(ω,T e1) rather than the Fresnel coefficients determines essentially this temperature dependence. Most interestingly we find frequency ranges where I (2)(ω,T e1) increases for small light intensities, while it decreases for large light intensities. Our theory yields also that SHG probes effects due to hot electrons more sensitively than linear optics. The results of our calculations are compared with recent experiments on Cu and Au. 相似文献
4.
We have performed four-beam time-resolved stimulated Raman measurements on liquid CS2. To interpret our results we have applied the response formalism for the third-order polarization to such an experiment. It turns out that the measured quantity is proportional to (a convolution of) Abs[χ(3)(-ωs, ωs, ωl, -ωl)]. As a consequence in this four-beam e xperiment one picks up electronic contributions in contrast to a two-beam experiment where Im[χ(3)] is observed. 相似文献
5.
In its simple form, the relaxation time of the Néel relaxation process of the magnetic moment of single-domain particles is given by τN=τ0Nexp(σ), σ being the ratio of anisotropy energy to thermal energy. The pre-factor, τ0N, is normally given a value of 10−9 s, but values ranging from 10−8 to 10−12 s have been reported in literature. Here, by means of the field and frequency dependence of the complex magnetic susceptibility, χ(ω,H)=χ′(ω,H)−iχ″(ω,H), of a magnetic fluid sample, in the MHz-GHz range, in conjunction with the determination of the sample decay function, b(t), the pre-factor τ0N is determined. b(t) is readily obtained through the inverse Fourier transformation relationship, which exists between b(t) and χ″(ω). 相似文献
6.
The a.c. conductivity σ(ω) of ionic materials takes the form, σ(ω) = σ(0) + Aωn. The carrier hopping rate, ωp, is obtained from the new expression σ(0) = A ωpn and the carrier concentration is estimated from σ(0). The contribution of creation and migration terms to the activation energy for conduction may be determined from the thermal activation of σ(0) and ωp and the corresponding entropy terms quantified. Data have been analyzed for four widely different ionic materials: single crystal Na β-alumina, polycrystalline Li4SiO4, Ag7l4AsO4 glass and Ca(NO3)2/KNO3 glass and melt. For each, the carrier concentration and hopping rates have been obtained. 相似文献
7.
P.C. Fannin C. MacOireachtaigh C. Couper 《Journal of magnetism and magnetic materials》2010,322(16):2428-2433
Measurements by means of the short-circuit (S/C) and open circuit (O/C) transmission line techniques are well established methods for investigating the magnetic and dielectric properties of magnetic colloids, respectively. In particular, the S/C technique has been used in the investigation of the resonant properties of ferrofluids; resonance being indicated by the transition of the real component of the magnetic complex susceptibility, χ(ω)=χ′(ω)−iχ″(ω), from a positive to a negative value at a frequency, fres. However, under certain circumstances, the accuracy of the S/C technique is affected by the dielectric properties of the sample, hence incurring errors in the measurement of χ(ω) and indeed of fres. Here we present a model which, by combining short-circuit and open circuit measurements, is developed in a manner in which the permeability, μ, and the permittivity, ε, contribute simultaneously to the calculation of χ(ω), thereby providing superior experimental results in comparison to those obtained by the S/C technique alone. For the two ferrofluid samples measured it is demonstrated that the dielectric properties affect the high frequency content of the susceptibility spectrum. 相似文献
8.
P.C. Fannin 《Journal of magnetism and magnetic materials》2009,321(7):850-853
Measurement of the magnetic complex susceptibility, χ(ω)=χ′(ω)−iχ″(ω) by means of the transmission line technique, is a well established method for the determination of the dynamic properties of nano-particle colloids, such as magnetic fluids. From polarising studies one can obtain accurate data on the anisotropy constant, K, anisotropy field, HA, gyromagnetic constant γ, and the damping parameter, α. From data on χ(ω), one can determine the loss tangent, tan δ, of the samples and also a value of the precessional decay time, τ0. From polarized studies, one can investigate the presence of any hysteresis. The technique is also suitable for the investigation of the magnetic properties of composite samples. In this paper a review of the above mentioned topics are presented with examples of results obtained for a number of magnetic fluids. 相似文献
9.
Holger Lutz Jochen Hoffmann Alois Seilmeier Wolfgang Schnick 《Journal of Physics and Chemistry of Solids》2004,65(7):1285-1290
Nitridosilicates are of interest as novel nonlinear materials due to their extraordinary chemical and thermal stability. Unfortunately, large nitridosilicate single crystals are presently not available for the investigation of their nonlinear optical properties. The first experiments are presented in which an averaged nonlinear susceptibility χ(2) for several nitridosilicates is studied by using two different powder techniques, the Kurtz Perry method and the SHEW method (Second Harmonic Wave generated by an Evanescent Wave). We observe nonlinearities of the new materials which are comparable to those of LiIO3. The highest averaged Meff=(χeff(2))2/4n2ωnω2 values found are ∼0.9 pm2/V2. The refractive indices of the materials are determined to be between n=2 and 3. 相似文献
10.
《Physics letters. A》1997,234(4):310-317
We present a general formalism of the NLO susceptibilities by using the Genkin-Mednis approach for a one-dimensional electron-lattice system. Based on the SSH model, we obtained an analytic expression for the third-order nonlinear optical susceptibilities χ(3)(ω) for polydiacetylenes (PDAs) after considering the case of conjugated chains, in which there is no adjustable parameter. The results are in good agreement with experiments on PDAs. Furthermore, the origin of the second peak in the χ(3)(ω) spectrum of PDAs is discussed, and a transition mechanism is proposed. It is believed that when the external light field is applied along the centrosymmetric polymer backbone, the parity symmetry of the system is broken, there occurs a mixing between the even- and odd-parity exciton states, leading to the transition from the ground state to the Ag excited state, and accordingly a second sharp peak appears in the χ(3)(ω) spectrum which could be attributed to the three-photon resonance with the Ag exciton generation process at around 2.2 eV. 相似文献
11.
In the frame work of TREDER 's gravitational theory we consider two classes of field equations which are derivable from two classes of LAGRANGE ian densities Ω(1)(ω1, ω2), Ω(2)(s?1, s?2). ω1, ω2; s?1, s?2 are parameters. Ω(2)(ω1, ω2) gives us field equations which are up to the post-NEWTON ian approximation in the sense of NORDTVEDT , THORNE and WILL equivalent to the field equations given by BRANS and DICKE . For ω2 = ?1 ?2ω1 field equations follow from Ω(1)(ω1, ?1 ?2ω1) which are in the above mentioned sense of post-NEWTON ian approximation equivalent to EINSTEIN 's equations. The field equations following from Ω(1)(ω1, ω2) have a cosmological model with the well known cosmological singularities for T → ± ∞ in case that ω1/(1 +3ω1 +ω2) ? γ > 0. For ω1/(1 +3ω1 +ω2) ≤ 0 cosmological models with no cosmological singularities exist. From Ω(2)(s?1, s?2) we obtain field equations which at the best give us perihelion rotation 7% above EINSTEIN 's value and light deflection 7% below the corresponding EINSTEIN 's value. But in that case we are able to show the existence of a cosmological model without any cosmological singularity. 相似文献
12.
The stability of large Fröhlich bipolarons in the presence of a static magnetic field is investigated with the path integral formalism. We find that the application of a magnetic field (characterized by the cyclotron frequence ω c) favors bipolaron formation: (i) the critical electronphonon coupling parameter α c (above which the bipolaron is stable) decreases with increasing ω c and (ii) the critical Coulomb repulsion strength U c (below which the bipolaron is stable) increases with increasing ω c. The binding energy and the corresponding variational parameters are calculated as a function of α, U and ω c. Analytical results are obtained in various limiting cases. In the limit of strong electron-phonon coupling (α ? 1) we obtain for ω c ? 1 that E estim ? E estim(ω c = 0) + c(u)ω c/α 4 with c(u) an explicitly calculated constant, dependent on the ratio u = U/α where U is the strength of the Coulomb repulsion. This relation applies both in 2D and in 3D, but with a different expression for c(u). For ω c ? α 2? 1 we find in 3D E estim ? ω c - α 2 A(u) ln2(ω c/α 2), (also with an explicit analytical expression for A(u)) whereas in 2D E estim 2D ? ω c - α√ω cπ(u-2-√2)/2. The validity region of the Feynman-Jensen inequality for the present problem, bipolarons in a magnetic field, remains to be examined. 相似文献
13.
The effect of a magnetic field on phase transitions in the Heisenberg ferromagnet Cu(NH4)2Br4·2H2O is investigated. It is found that the singularity shift of the susceptibility χ(P, T) in a magnetic field is approximated by power functions with the indexes ω = 2.5 and ? = 0.58. 相似文献
14.
Dr. Egon Becker 《Zeitschrift für Physik B Condensed Matter》1968,8(3):216-240
GdCl3 is a ferromagnet with two equivalent sub-lattices in which the dipolar interaction is comparable with the exchange interaction. In the Callen decoupling approximation the time and temperature dependent Green’s functions are derived and the transversal complex susceptibilitiesχ xx(ω,h 0) andχ yx(ω,h 0) are calculated. The energies of the acoustical and the optical spinwave modes following from the Green’s functions are renormalized by the magnetization and the spin correlation. The spinwave spectrum, showing an unusual angular dependence, is calculated analytically in the whole Brillouin zone and numerically in the long wavelength region. 相似文献
15.
E. Carbia-RuelasM.E. Sánchez-Vergara V. García-MontalvoO.G. Morales-Saavedra J.R. Álvarez-Bada 《Applied Surface Science》2011,257(8):3313-3319
In this work, the synthesis of molecular materials formed from A2[TiO(C2O4)2] (A = K, PPh4) and 1,8 dihydroxyanthraquinone is reported. The synthesized materials were characterized by atomic force microscopy (AFM), infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy. IR spectroscopy showed that the molecular-material thin-films, deposited by vacuum thermal evaporation, exhibit the same intra-molecular vibration modes as the starting powders, which suggests that the thermal evaporation process does not alter the initial chemical structures. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.003-1.16 eV, were calculated from Arrhenius plots. Optical absorption studies in the wavelength range of 190-1090 nm at room temperature showed that the optical band gaps of the thin films were around 1.9-2.3 eV for direct transitions Egd. The cubic NLO effects were substantially enhanced for materials synthesized from K2[TiO(C2O4)2], where χ(3) (−3ω; ω, ω, ω) values in the promising range of 10−12 esu have been evaluated. 相似文献
16.
Uhlmann's transition probability P(ψ, φ) of two normal states of a von Neumann algebra M, which is the supremum of |(Ψ, Φ)|2 for all possible choices of representative vectors Ψ and Φ of ψ and φ, is shown to be the infimum of (∫d(μψ, e)1/2)2 for the induced measures μω, e(B)=ω(e(B)) (B: Borel set in ℝ, ω=ψ, φ) for all possible projection-valued measures e belonging to M. 相似文献
17.
本文求出了Eliashberg方程在T=Tc时的解,得到了下面的临界温度级数表示式:Tc=α0(μ*)(λ〈ω2〉)1/2{1+1/λα1(μ*)〈ω4>/〈ω2>2+1/λ2(α21(μ*)〈ω6>/〈ω2>3+α22(μ*)〈ω4>2/〈ω2>4) +1/λ3(α31(μ*)〈ω8>/〈ω2>4+α32(μ*)(〈ω4>〈ω6>)/〈ω2>5)+α33(μ*)〈ω4>3/〈ω2>6+…},其中α0(μ*),α1(μ*)等仅是μ*的函数。新的Tc公式表明了,Tc不仅依赖于λ、μ*和〈ω2〉,而且依赖于有效声子谱α2F(ω)的各级矩〈ω2n〉。 相似文献
18.
Non-degenerate four-wave mixing using two non-collinear laser beams with frequencies (wavevectors) ωp, ωt (kp, kt) respectively is studied in CuCl. Two emission lines at frequencies ω(1)=2ωt-ωp, and ω(2)=2ωp-ωt are observed. Their excitation spectrum is sharply peaked if the phase-match condition k(1)=2kt-kp is fulfilled. This is the case, if ωp coincides with the hyper-Raman lines (R+T, R-T) of the laser labelled (t) in a well-defined geometrical configuration. 相似文献
19.
Sergio Albeverio Jens-Erik Fenstad Raphael Høegh-Krohn Witold Karwowski Tom Lindstrøm 《Physics letters. A》1984,104(8):396-400
We discuss hamiltonians in L2(Rd, dx) of the form H = ?Δ + V, with V a potential supported by a zero measure set C. In particular if C is a path of a brownian motion b such that V(x) = ∫01λ(x, ω)δ(x-b(s, ω)) ds, we show that H exists as a nontrivial, self-adjoint, lower bounded perturbation of ?Δ when d ?5. We must choose λ to be an infinitesimal, negative function for d = 4,5, but for d ? 3 any bounded real-valued function λ will do. The connection with Edward's model of polymers as well as with quantum fields of the ?d4-type is also discussed. The proofs use methods of nonstandard analysis. 相似文献