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1.
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)=2ωtp, and ω(2)=2ωpt 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   

2.
A nonlinear optical method to determine the transverse relaxation time of excitonic molecules by means of two-photon echo is proposed. In the case of two-photon transition such as excitonic molecule one needs three pulses to obtain an echo signal. When the wave-vector and frequency of the three successive pulses are denoted by k11, k22 and k33, the two-photon echo can be observed in the direction of 4k2-2k1-k3 with frequency 4ω2-2ω13. Tuning both ω1 and ω2 to be two-photon resonant with excitonic molecule, we can satisfy the phase-matching condition rather easily for appropriate values of ω3 due to the large dispersion of excitonic polaritons. From the correlation trace of the two-photon echo we can determine directly the transverse relaxation time of excitonic molecules.  相似文献   

3.
Evidence is presented for a newK * \(\bar K\) +c.c. resonance with a mass of (1,526±6) MeV, a width of (107±15) MeV and quantum numbersIJ PC=01++. We call itD′ meson. Initially it is observed as aK * \(\bar K\) +c.c. enhancement in the reactionsK ? p→(K s 0 K ±π?)Λ at 4.2 GeV/c. The isospin assignmentI=0 comes from its further observation in the reactionsK ? p→(K s 0 K ±π?)Σ 0 andK ? p→(K s 0 K ±π?)Σ(1,385)0 but not inK ? p→(K + K ?π?+ orK ? p→(K s 0 K ±π?)Σ(1,385)+. A maximum likelihood analysis of the (K \(\bar K\) π) decay Dalitz plots in the reactionsK ? p→(K s 0 K ±π?) determines theJ PC of theD′ meson to be 1++. A satisfactorySU(3) fit is obtained to a 1++ nonet composed of theI-1A 1, theI=1/2Q A with theD(1,285) and theD′(1,526) as theI=0 members having a mixing angle close to the magic one.  相似文献   

4.
The first observation of interference effects between two sharp resonant contributions to the third-order nonlinear susceptibility χ(3)3012) is reported. Using two tunable near ir frequencies, ω01 and ω2, the was seen in crystalline CuCl when 2ω1 and ω12 were close to the sharp Z3 exciton at 3.21 eV and the 210 cm-1 Raman line, respectively. Three different tunable visible frequencies were used to observe similar interference effects in a benzene-cyclohexane mixture when ω02 and ω12 were close to the 992 cm-1 Raman line of benzene and the 801 cm-1 Raman line of cyclohexane, respectively.  相似文献   

5.
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   

6.
By taking due account of momentum conservation, it is shown that, when ω is near the Fermi energy ωF, the imaginary part of the mass operator M(k, ω) for an infinite Fermi system behaves like (ω ? ωF)p(k) where the exponent p(k) ? 2 depends on the interval in which |k| is lying. In particular, the commonly asserted quadratic behaviour (ω ? ωF2 is shown to be true only for |k| ? 3kF. It is explicity assumed that the Fermi system admits a perturbative type treatment.  相似文献   

7.
8.
A high-power sub-millimeter wave propagating through bismuth, a semimetal with non-spherical energy surfaces, parametrically excites a space-charge mode and a back-scattered electromagnetic wave. The free carrier density perturbation associated with the space-charge wave couples with the oscillatory velocity due to the pump to derive the scattered wave. The scattered and pump waves exert a pondermotive force on electrons and holes, driving the space-charge wave. The collisional damping of the decay waves determines the threshold for the parametric instability. The threshold intensity for 20 μm wavelength pump turns out to be ∼2×1012 W/cm2. Above the threshold, the growth rate scales increase with ωo, attain a maximum around ωo=6.5ωp, and, after this, falls off.  相似文献   

9.
余玮  徐至展 《物理学报》1987,36(7):992-997
本文研究了激光拍频波加速器中的三波相互作用过程。结果表明:适当地选择参数σ=ωp/(ω12)以及β=ω21p12分别为等离子体频率及两束激光频率),即可用较弱的激光造成很强的拍频等离子体波,并使注入等离子体的电子获得显著的能量增益。 关键词:  相似文献   

10.
A uniformly rotating frame is defined as the rest frame of a particle revolving with constant velocityω in a circle about theZ-axis of an inertial frame Σ0. Under the conditionz=Z,r=R, theoretical constraints are established for the solution of the transformation problem Σ0→Σω rω r being the cylindrical subframe of Σω. The unique solution of the problem in cylindrical coordinates is isomorphic to the special Lorentz transformationL x, withβ=v/c replaced byβ r=ωr/c. Hence the intrinsic geometry on the surface of a rotating cylinder is Euclidean. Though there exists no complete intrinsic geometry on the surface of a rotating disk, the geodesics on it are straight lines while the circumference of a concentric circle isK r2πr as predicted by Einstein.  相似文献   

11.
The reaction γp →ωp(ω → π+π?π0 and π0 → γ γ) has been studied in ep interactions using the ZEUS detector at photon-proton centre-of-mass energies between 70 and 90GeV and ∣t∣ < 0.6GeV2, where t is the squared four momentum transferred at the proton vertex. The elastic ω photoproduction cross section has been measured to be σγp → ωp = 1.21 ±0.12 ±0.23 μb. The differential cross section dσγp→ωp/d¦t¦ has an exponential shape e?b∣t∣ with a slope b =10.0 ± 1.2 ± 1.3 GeV?2. The angular distributions of the decay pions are consistent with s-channel helicity conservation. When compared to low energy data, the features of ω photoproduction as measured at HERA energies are in agreement with those of a soft diffractive process. Previous measurements of the ρ0 and ? photoproduction cross sections at HERA show a similar behaviour.  相似文献   

12.
Vk centers (self trapped hole I?2) have been obtained in CsI doped with Tl+ or Na+ by X-irradiation at low temperature and studied by ESR. Spin-Hamiltonian parameters are calculated and compared with those obtained for I?2 in the other alkali iodides, as well as the energy of the forbidden transition 2Σ+u2Πu and the s and p components of the fundamental state.  相似文献   

13.
The backward production of the B(1235) meson is studied in the reaction K?pΣ?π+ω. This reaction is observed in the final state Σ?π+π+π?π0. A π+ω mass enhancement is visible in the region of the B meson for events with small |u|K?Σ?) squared four-momentum transfer. The properties of the enhancement agree with those of the B meson. The cross section for K?pΣ?B+ at 4.15 GeVc incident K? momentum is (3.2 ± 0.5) μb. The backward production of the B meson is compared with similar baryon exchange productions of the A1 and C(Q1) axial vector mesons observed in the same experiment.  相似文献   

14.
Coherent excitation of the soft polariton mode in BaTiO3 is obtained by a two-beam method. The relative power variation on one beam is measured as a function of the polariton frequency (0 < ωp < 30 cm?1) for a scattering angle of 0.14° (|kp| ? 4500 cm?1) and shows a maximum at ωp ? 13 cm?1. By fitting experimental results to the theoretical power variations, the atomic displacive coefficient is determined.  相似文献   

15.
The degree of purity of the quantum state of electromagnetic field at the output of a degenerate optical parametric oscillator is theoretically analyzed. It is shown that, in the subthreshold and significantly suprathreshold modes, the degree of purity of the state of pairs of waves with frequencies ω s ± Ω (ω s is the signal mode frequency) is unity. Based on this fact, it is concluded that these pairs of waves parametrically develop independent of any other such pairs. At the same time, in the suprathreshold mode near the oscillation threshold, the degree of purity of wave pairs can be much smaller than unity. However, consideration of a tetrad of waves with frequencies ω s ± Ω and ω p ± Ω shows that this system is in a pure state, which indicates its independent development.  相似文献   

16.
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   

17.
An attempt is made to explain the lower resonance anomaly in the thermal conductivity of Ni-doped Al2O3 by using τr ~ ω-4s2 ? ω2r)2. An agreement between theory and experiment needs s = 0.71, and this is interpreted to mean that the frequency dependence of impurity-phonon coupling is approximately described by ω0.71 for phonons having frequencies in close neighbourhood of ωr.  相似文献   

18.
Hidekatsu Nemura 《Few-Body Systems》2013,54(7-10):1223-1226
We present our recent study on ΛN and ΣN (isospin I = 3/2) interactions by measuring Nambu–Bethe–Salpeter wave functions on the Lattice QCD. The lattice QCD calculation is performed by using the N f  = 2 + 1 gauge configurations generated by PACS-CS collaboration together with employing an improved method to obtain potentials in lattice QCD simulations. For the 1 S 0 channel, the central ΣN (I = 3/2) potential and the central ΛN (1 S 0) potential are found to be very similar. For the spin triplet (3 S 1?3 D 1) channels, the central ΛN(3 S 1?3 D 1) potential is attractive while the central ΣN(I = 3/2, 3 S 1?3 D 1) potentials is repulsive. Tensor potentials, on the other hand, are rather weak in both ΛN and ΣN(I = 3/2) systems.  相似文献   

19.
It is shown that recent measurements of field ion energy distributions from clean tungsten surfaces probe the density of metal states in the vicinity of the surface. We find j(ω) = (2π/kh)Σm| ∫ d3m(r)γz|2δ(ω??m), where j(ω) is the ion current a ω, ψmand ?m are electronic metal eigenfunctions and eigenvalues in the presence of the external electric field used in field ionization and γ(z) is a function which is large near the noble gas atom. An explicit expression for γ(z) is given in the text. It is estimated that tungsten metal states with values of k6 at least as large as 0.5 Å?1 make an appreciable contribution to j(ω) where k6 is the electron momentum parallel to the surface.  相似文献   

20.
Second-harmonic generation in the field of an ultrashort pulse and the propagation of extremely short pulses in a medium with quadratic nonlinearity are analyzed. Second-harmonic generation is analyzed taking into account the effect of second-and third-order group velocity dispersion and dispersion of nonlinear susceptibility up to the second order. Corrections, whose order of smallness is determined by the parameter (ωL t p)?1, where t p is the pulse duration and ωL is the carrier frequency of the pump wave, are obtained. For a large phase mismatch, two new solutions are found that describe the stationary evolution of solitary pump and second-harmonic waves in the regions of both anomalous and normal group velocity dispersions.  相似文献   

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