BaTiO3:Ce自泵浦相位共轭产生机理随泵浦光斑尺寸的变化

实验发现当光入射到晶体表面的泵浦光斑尺寸较小时,无论入射角和入射位置怎样,擦除光对相位共轭反射率没有影响,同时从上表面可观察到全内反射的光回路,所以SPPC的形成机理为FWM-TIR;当入射到晶体表面的泵浦光斑尺寸较大时,在一定的入射角和入射位置,擦除光的作用使相位共轭反射率很快减小,表明这时的SPPC的形成机理为FWM-SPB.     

Photoproduction of Θ and other pentaquark states

We present constraints on the relative photoproduction cross sections of positive parity pentaquark states, Σ₅, Λ₅, and N₅, based on a minimum phenomenology gained in and their baryon–meson couplings as in the work of Close and Dudek. The possibility of anomalous signals in γp→K⁰_S(Θ⁺;Σ_d⁺) is discussed. We emphasize the importance of comparing with “conventional” states such as γN→KΣ(1660).     

Non-1/mb power suppressed contributions to inclusive B → Xsll decays

We compute non-perturbative contributions to B → X_sl⁺l⁻ that are not explicitly suppressed by powers of the b-quark mass. They are proportional to and arise from an interference between the free-quark amplitude and high order terms in the matrix element of the four-quark operator s⁻γ^μ(1 − γ₅)cc^−βγ_μ(1 − γ₅)b_β. This correction is found to be small over most of the dalitz plot except near the charm threshold. Unfortunately, the perturbative computation we have performed is invalid near charm threshold and we do not except to see the structure found at lowest order reproduced in the data. We conclude that these non-perturbative contributions do not significantly modify the previous analysis of B → X_sl⁺l⁻.     

Supersymmetric contributions to direct CP violation in K→ππγ decays

We analyze the supersymmetric contributions to direct–CP–violating observables in K→ππγ decays induced by gluino–mediated magnetic–penguin operators. We find that ε′_+−γ and the differential width asymmetry of K^±→π^±π⁰γ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where ε′/ε is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in |ΔS|=1 transitions, complementary to ε′/ε and rare decays.     

On the pp → ppη(η′) reactions near threshold

The production rate for η′ in pp → ppη′ at rest is calculated in a covariant one boson exchange model, previously applied to study π⁰ and η production in NN collisions. The transition amplitudes for the elementary BN → η′N processes with B being the meson exchanged (B = π, σ, η, , ω and a₀) are taken to be the sum of s- and u-channels with a nucleon in the intermediate states, and an a₀ meson pole in a t-channel. The couplings of the η′ to hadrons are a factor 0.4 weaker than the respective η-hadron couplings, as suggested by a quark model and a singlet-octet mixing angle θ = −23°. The model reproduces near threshold cross sections for the quasielastic processes π⁻p → nη(η′) and pp → ppη(η′) reactions.     

Minimal SUSY SO(10), b–τ unification and large neutrino mixings

We show that the assumption of type II seesaw mechanism for small neutrino masses coupled with b–τ mass unification in a minimal SUSY SO(10) model leads not only to a natural understanding of large atmospheric mixing angle (θ₂₃) among neutrinos, as recently noted, but also to large solar angle (θ₁₂) and a small θ₁₃≡U_e3 as required to fit observations. No additional symmetries are required to obtain large neutrino mixings. The proposed long baseline neutrino experiments will provide a crucial test of this model since it predicts U_e30.16.     

The ΔNγ electromagnetic transition form factors GM(q) and GE(q)

A parameter-free, nonperturbative calculation of the ΔNγ electromagnetic transition amplitudes GM*(q2), GE*(q2), and the resonant multipole ratio REM(q2)≡E1+3/2(q2)/M1+3/2(q2) is performed in terms of the well-known nucleon isovector Sachs form factor GMV. Our methods are fully relativistic with conservation of the electromagnetic current guaranteed. We find that GM*(q2) decreases more rapidly than the nucleon dipole form factor when −q21 GeV2/c2 and that REM(q2) remains small even for very high four-momentum transfer implying that the perturbative QCD prediction REM(q2)→1 is purely asymptotic and is valid only for extremely high |q2|.     

Crystal growth and characterisation of new organic nonlinear optical materials: 6-cyano and 6-nitro-2,2-dimethyl-3,4-epoxychroman

Two chiral organic nonlinear optical materials, (3S,4S)-(−)-6-cyano-2,2-dimethyl-3,4-epoxychroman (1) and (3R,4R)-(+)-6-nitro-2,2-dimethyl-3,4-epoxychroman (2), have been grown into single crystals of cm³-size. Although both compounds crystallise in the orthorhombic P2₁2₁2₁ space group, they are not isomorphous and their crystal packings are quite different. Angle tuned type II phase-matched second harmonic generation between 0.8 and 1.064 μm has been evidenced, with effective nonlinear coefficients d_eff of 1 and 5 pm/V at 0.96 μm for 1 and 2, respectively. These values are in agreement with those estimated in the oriented gas model approximation using EFISH first order hyperpolarisability values (β₀=2.6 and 4.0×10⁻³⁰ esu for 1 and 2, respectively).     

Transient analysis of degenerate four-wave mixing in saturable absorbers: application to Cr:GSGG at 1.06 μm

We introduce a model of degenerate four-wave mixing in saturable absorbers in the transient regime when the interacting pulses have a duration much shorter than the lifetime of the excited-state level. Our model takes into account of the depletion and the mutual interaction of the pump waves. We study the influence of excited-state absorption on phase conjugate reflectivity. This theory agrees with experimental investigations made in Cr⁴⁺:GSGG with nanosecond pulses at λ₀ = 1.06 μm. A reflectivity of 0.6% is achieved and imaging capabilities are demonstrated.     

Exact analytical expressions for the dispersion relation of one-dimensional chiral photonic crystals

We consider one-dimensional photonic crystals made of alternating layers of two kinds of isotropic chiral media. The two layers are characterized by the dielectric permittivities ε₁ and ε₂, the magnetic permeabilities μ₁ and μ₂, the chirality parameters γ₁ and γ₂ and the thicknesses d₁ and d₂. By diagonalizing an 8 × 8 matrix derived from the two coupled wave equations satisfied by our system, we obtain exact analytical expressions for the dispersion relation for plane electromagnetic waves propagating at an arbitrary angle with respect to the layers. We present a detailed analysis of our dispersion relation and explore the evolution of the photonic band structure as the frequency, the chirality parameter and the incident angle vary, with a special emphasis on the generation of the cross- and co-polarization bandgaps.     

On the “quantum rainbow” in surface scattering

In this letter we propose a new method to compute the scattering amplitudes of atoms from a corrugated wall model of a crystal surface. The method method requires reasonable computing time and converges rapidly to the solution of the scattering amplitudes (within 0.01% in each beam and satisfying unitarity) for any corrugation such that kζ₀ < 4.5 and ζ₀ < 0.35 Å, where k is the magnitude of the incident wave vector and ζ₀ the amplitude of the corrugation. These conditions for kζ₀ and ζ₀ are satisfied for any crystal surface and light scattering atoms (H and He) at thermal energies which makes the method appropriate for the system He, LiF for which results are presented comparing them with recent experimental data.     

Optical absorption, disorder and the Anderson transition

The optical gap, E_g, of amorphous indium-oxide films is measured as a function of static disorder near the metal-insulator transition. On the insulating side of the transition the optical gap obeys a scaling relation, ΔE_g = -E_*Δg where E_* is of the order of the Fermi energy of the given sample and g≡K_Fl. These results are ascribed to the continuous shift of the mobility-edge in the conduction band with disorder.     

Investigation of light scalar resonances a0(980)/ƒ0(980) with ANKE

A program to investigate the light scalar resonances a₀(980)/ƒ₀(980) in hadronic interactions via their decay into the πη and channels has started at the ANKE spectrometer of COSY-Jülich. As the first step the reactions pp → dπ⁺X and pp → dK⁺X have been measured at two energies, T_p = 2.65 GeV and 2.83 GeV. The status of the analysis at T_p = 2.65 GeV is presented. A total cross section of about 50 nb has been determined for the reaction .     

Mössbauer investigations on Np3S5

The 59.5 keV Mössbauer resonance of ²³⁷Np has been measured in Np₃S₅ at 77 and 4.2 K. At 77 K, two different quadrupolar splittings are observed. The first one (δ₁ = −5(1) mm sec⁻¹/NpAl₂) is assigned to the Np⁴⁺ ions and the second one (δ₂ = 28(1) mm sec⁻¹/NpAl₂) is assigned to the Np³⁺ ions. At 4.2 K the spectrum gives a ratio of areas S(Np³⁺)/S(Np⁴⁺) of 2.0. These results clearly confirm the crystallographic data of this mixed-valence material.     

Symmetry breaking and the decays ψ′ → J/ψπ(η) and J/ψ → η(η′) γ

The theoretical mechanisms for the decays ψ′ → ψπ⁰ and ψ′ → ψη, which violate SU₂ and SU₃, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π⁰ −η −η′ mixing. The π⁰ −η mechanism ψ′ → ψν → ψπ⁰ leads to Γ(ψ′ → ψπ⁰) = (3.3±1.0) × 10⁻³ Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π⁰−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed.     

Measurement of apex angle of the prism using total internal reflection

Total internal reflection technique is examined critically for the measurement of apex angle of the prism. Recognition of the critical boundary completely specifies the apex angle ‘A’ of the prism by keeping constant the ratio of refractive index of sample fluid (n₁=1.4) to that of glass (n₂=1.7). Recording of observations in the laboratory is dependent upon whether the apex angle ‘A’ of prism is greater than or less than or equal to critical angle ‘r_c’. The minimum value of error function ‘χ’ in the proximity of Abbe angle explain the choice of Abbe type instruments and shown invariant by relating positive ‘₊’ and the negative angle of emergence ‘₋’. Using ray-tracing technique, an expression for the length of the critical boundary ‘l’ is derived and is shown as a measure of the apex angle ‘A’ of the prism.

The choice of the realistic grazing condition leads us to two turning points for which error function ‘χ’ is minimal and yields appropriate option of the measurement of apex angle ‘A’ of the prism. It is further shown that the small error ‘ζ’ crept in the apex angle ‘A’ of the prism can lead to a significant error in the design of Pulfrich type instruments.

Experimental measurements are in-line with the predictions made.     

Determination and analysis of the dispersive optical constants of the 5,5′,6,6′-tetraphenyl-2,2′-bi([1,3]dithiolo[4,5-b][1,4]dithiinylidene)–DDQ complex thin film

The synthesis and optical properties of the 5,5′,6,6′-tetraphenyl-2,2′-bi([1,3]dithiolo [4,5-b] [1,4]dithiinylidene)–2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) complex thin film were investigated by the optical characterization. The optical constants such as refractive index, extinction coefficient and absorption coefficient were determined using the transmittance T(λ) and reflectance R(λ) spectra and the refractive index dispersion was analyzed using single oscillator of Wemple–Didomenico model. The single oscillator energy E₀ and the dispersion energy E_d were calculated. The effect of temperature on refractive dispersion and optical band gap E_g is also discussed. As a result, the annealing temperatures have an important effect on refractive index of thin film.     

Two-loop renormalization of tanβ and its gauge dependence

Renormalization of two-loop divergent corrections to the vacuum expectation values (v₁,v₂) of the two Higgs doublets in the minimal supersymmetric standard model, and their ratio tanβ=v₂/v₁, is discussed for general R_ξ gauge fixings. When the renormalized (v₁,v₂) are defined to give the minimum of the loop-corrected effective potential, it is shown that, beyond the one-loop level, the dimensionful parameters in the R_ξ gauge fixing term generate gauge dependence of the renormalized tanβ. Additional shifts of the Higgs fields are necessary to realize the gauge-independent renormalization of tanβ.     

Structural and lithium intercalation studies of Mn(0.5−x)CaxTi2(PO4)3 phases (0≤x≤0.50)

Materials from the Mn_(0.5−x)Ca_xTi₂(PO₄)₃ (0≤x≤0.50) solid solution were obtained by solid-state reaction in air at 1000 °C. Selected compositions were investigated by powder X-ray diffraction analysis, ³¹P nuclear magnetic resonance (NMR) spectroscopy and electrochemical lithium intercalation. The structure of all samples determined by Rietveld analysis is of the Nasicon type with the R space group. Mn²⁺/Ca²⁺ ions occupy only the M1 sites in the Ti₂(PO₄)₃ framework. The divalent cations are ordered in one of two M1 sites, except for the Mn_0.50Ti₂(PO₄)₃ phase, where a small departure from the ideal order is observed by XRD and ³¹P MAS NMR. The electrochemical behaviour of Mn_0.50Ti₂(PO₄)₃ and Mn_(0.5−x)Ca_xTi₂(PO₄)₃ phases was characterised in Li cells. Two Li ions can be inserted without altering the Ti₂(PO₄)₃ framework. In the 0≤y≤2 range, the OCV curves of Li//Li_yMn_0.50Ti₂(PO₄)₃ cells show two main potential plateaus at 2.90 and 2.50–2.30 V. Comparison between the OCV curves of Li//Li_(1+y)Ti₂(PO₄)₃ and Li//Li_yMn_0.50Ti₂(PO₄)₃ shows that the intercalation occurs first in the unoccupied M1 site of Mn_0.50Ti₂(PO₄)₃ at 2.90 V and then, for compositions y>0.50, at the M2 site (2.50–2.30 V voltage range). The effect of calcium substitution in Mn_0.50Ti₂(PO₄)₃ on the lithium intercalation is also discussed from a structural and kinetic viewpoint. In all systems, the lithium intercalation is associated with a redistribution of the divalent cation over all M1 sites. In the case of Mn_0.50Ti₂(PO₄)₃, the stability of Mn²⁺ either in an octahedral or tetrahedral environment facilitates cationic migration.     

Stokes parameters measurement of light over a wide wavelength range by judicious choice of azimuthal settings of quarter-wave plate and linear polarizer

The Stokes parameters (S_p, S₁, S₂, S₃) of light are measured at an arbitrary wavelength over a wide wavelength range. The Stokes parameters S₁ and S₂ are easily obtained. But the Stokes parameter S₃ at the arbitrary wavelength is affected by the phase difference error Δ₁ of the quarter-wave plate mismatch and the Stokes parameters S₁ or S₂. Therefore, in this paper, S₃ is obtained from both the intensity measurements by the circular polarizer rotating the quarter-wave plate by 0° and 90°. Then, S₃ is obtained by considering only Δ₁, but is not affected by S₁ and S₂. Also, though Δ₁ is not accounted for, S₃ is measured more accurately.