多层介质膜脉冲压缩光栅近场光学特性分析

利用傅里叶模式理论分析了TE波自准直角入射的使用条件下，多层介质膜光栅的光栅区和多层膜区电场分布的特点.分别讨论了HfO₂和SiO₂为顶层光栅材料时，光栅结构参数对光栅脊峰值电场的影响，结果表明，对于不同膜厚的顶层材料，存在一个最佳膜厚度，使光栅脊峰值电场最小，并且当膜厚增大时，设计大高宽比的光栅可以降低该电场峰值.最后，在大角度条件下使用多层膜光栅也可以降低光栅脊处的峰值电场. 关键词： 衍射光学 多层介质膜光栅 模式理论 损伤阈值     

Near-field optical properties of wide bandwidth metal multi-layer dielectric gratings for pulse compressor

Metal multi-layer dielectric gratings (MMDG) for pulse compressors in high-energy laser systems should provide broad bandwidth as well as high laser-induced damage thresholds. The non-uniform optical near-field distribution of MMDG is an important factor that limits damage resistant capabilities. MMDG for pulse compressors operating at 800 nm with a corrugated SiO₂ layer are designed by using a genetic algorithm and the Fourier mode method. The diffraction efficiency, bandwidth, and near-field distribution of the MMDG are theoretically investigated. For the single dielectric match layer grating, the bandwidth is 140 nm, if the thickness and refractive index of the match layer are changed, the maximum electric field in the grating ridge, match layer, and metal layer of the grating increases with the decrease in grating diffraction efficiency. For the multi-dielectric match layer grating, the bandwidth and the maximum electric field in the metal layer decrease with the increase in high- and low-index material pairs, and the maximum electric field in the grating ridge and match layer initially decreases and then increases. Over a wide wavelength range, the maximum electric field in the grating ridge, match layer, and metal layer is minimal near the central wavelength. Moreover, MMDG should be used at larger incident angles while keeping enough bandwidth to reduce the electric field in the grating.     

Quantum-statistical mechanics of a system of charged particles at high temperatures

If a quantum-mechanical potential is introduced the calculation of the quantummechanical binary distribution function for a system with Coulomb interaction is reduced to the well-known mathematical formalism of classical statistical mechanics in the case ofnλ³?1 (λ being the thermal wavelength). The two-particle quantummechanical potential is determined by the two-particle Slater sum. In this paper we calculated the two-particle Slater sum using an expansion according toe ² and the resolvent formalism. From the binary distribution function the correlation energy and the free energy as well were determined up to ordere ⁶. Symmetry effects were taken into account.     

Optical spectroscopy of surfaces: Reflectance studies of chemisorption

A high precision technique has been used to study the small changes in near-normal incidence reflectance R caused by chemisorption of gases on an atomically clean metal surface maintained in ultrahigh vacuum. Examples are given for O₂, CO, and H₂ on Mo(100) in the photon energy range 1.9 <?ω < 4.8eV. The relative reflectance change $\text{ΔR}\text{R}$ is negative and reaches as much as 1%. Structure that appears in ΔR(e), where e=exposure (pressure × time), is attributed to different binding configurations of the adatoms as observed, e.g., in LEED experiments. The dependence of $\text{ΔR}\text{R}$ on ?ω suggests the presence of adsorbate-induced surface states within a few eV of the Fermi energy. Possible approaches to determining the dielectric function of the surface region from the data are discussed.     

Self focusing of electromagnetic beams in InSb: Predominance of nonlocal effects

On the basis of a phenomenological treatment, the nonlinear dielectric constant of nondegenerate nonparabolic semiconductors like InSb (having both +e and ?e carriers) has been studied for Gaussian electromagnetic beams. The nonlinearity resulting from redistribution of carriers in the sample at low temperatures has been shown to be an order of magnitude higher than that due to the non-parabolicity of energy bands. Self focusing of electromagnetic beams as a result of these nonlinearities has been discussed.     

Forward-backward multiplicity distributions in the Peřina-McGill scheme and analysis ine + e − collisions

A forward-backward multiplicity correlation is considered by the use of the Pe?ina-McGill formula. We obtain analytic formulae for conditional cumulants of the backward multiplicity and a conditional backward multiplicity distribution at a given forward multiplicity. The multiplicity distribution and the conditional mean multiplicity observed at \(\sqrt s = 29\) in HRS ine ⁺ e ^? collisions are analysed. We predict the conditional moments and the conditional backward multiplicity distribution. Those should be compared with the future analyses in HRS.     

Tetragonal distortion of InAsPSb film grown on InAs substrate studied by Rutherford backscattering/channeling and synchrotron X-ray diffraction

Rutherford backscattering/channeling spectrometry and synchrotron X-ray diffraction are employed to characterize the structural properties of the InAsPSb epilayer grown on the InAs substrate. The results indicate that a 975-nm thick InAs_0.668P_0.219Sb_0.113 layer has a quite good crystalline quality (χ_min=6.1%). The channeling angular scan around an off-normal 〈1 1 1〉 axis in the (0 1? 1) plane of the sample is used to determine the tetragonal distortion e_T, which is caused by elastic strain in the layer. The results show that the InAsPSb layer is subjected to an elastic strain at the interfacial layer, and the strain decreases gradually moving towards the near-surface layer. It is expected that an epitaxial InAsPSb layer with the thickness of around 1700 nm will be fully relaxed (e_T=0). The magnitude difference of e_T deduced from angular scans and X-ray diffraction implies some structure (like dislocations) may play a role.     

Two-photon exchange in p⊆)p→ℓ+ℓ−X and a comparison with QCD

A thorough study of lepton-pair production from two-photon annihilation in p?)p collisions is presented. The differential cross section is calculated over a large range of energies (27?√s?800 GeV as a function of the dilepton mass M as well as the dilepton transverse momentum Q_T and the Feynman variable x_F. No kinematical approximations (such as the equivalent photon approximation) are made. For Q_T ≈ 0 the two-photon mechanism represents an important fraction of the pp→e⁺e^?X cross section already at ISR energies, whereas at ISABELLE energies it dramatically dominates in the interval 0?Q_T?1 GeV. At ISR energies these conclusions follow from a direct comparison of the two-photon contribution with pp→e⁺e^?X data. For the ISABELLE energy range the expected O(α_s) QCD contribution to pp→?⁺?^?X, corrected for soft gluon radiation to all orders (in leading bilogarithmic approximation), was taken as a reference. At larger Q_T and ISR energies the γγ contribution is negligible, whereas at √s = 800 GeV γγ/QCD? 10–20% almost everywhere. Furthermore, two-photon candidate events from the ISR are shown to be in reasonable agreement with theory. A decomposition of the γγ cross section into contributions from both proton vertices being elastic, inelastic and of mixed configuration is given. The results provide important clues for a future isolation of the two-photon mechanism.     

Surface plasmons in small metal particles

The dielectric response of a small metal particle to a perturbing potentialv _L =r ^L Y _LM e ^iωt is considered within the random phase approximation (RPA). The static dielectric polarizability is found and the size dependence of the surface plasmon frequencies are then determined from sum rule calculations. When the particle radiusa is large compared to the Thomas-Fermi screening lengthr ₀ the RPA equation is transformed into a form appropriate for an analytical solution. The dynamic electric polarizability, the position and the width of the surface plasma resonance are found in the limita/r ₀?1.     

Multiphotons trapping instability using fiber Bragg's grating potential perturbation for multiquantum bits encoding

We propose an interesting result of the trapped multiphotons distribution within a fiber Bragg's grating. The multitrapped photons are confined by the potential well, where the motion of photons in a fiber Bragg's grating is affected by the external perturbations, which they are defined as a series of nonlinear parametric in terms of potential energy. This investigation is modeled by using the nonlinear coupled mode equations and under Bragg's resonance condition, where the initial frequency of the light, ω₀ is the same value as the Bragg's frequency, ω_B. Results obtained have shown that the higher perturbation series represents the potential well is much differed from the equilibrium situation. In applications, the external perturbations on the fiber grating can cause the trapped photons instability, which introduces the escaped photons from the potential well being detected and observed. The potential of applications for quantum encoding device can be performed, which is analyzed and discussed in details.     

Broadening of ρ(→ e+e−) meson produced coherently in the photonuclear reaction

The e ⁺ e ^? invariant mass distribution spectra are calculated to estimate the hadron parameters of the ρ meson produced coherently in the photonuclear reaction. The elementary reaction occurring in the nucleus is considered to proceed as γN → ρ ⁰ N; ρ ⁰ → e ⁺ e ^?. We describe the elementary ρ meson photoproduction by the experimentally determined reaction amplitude $f_{\gamma {\rm N} \to \rho ^0 {\rm N}}$ . The ρ meson propagator is presented by the eikonal form, and the ρ meson nucleus optical potential V _Oρ appearing in it is estimated using the “t?” approximation. The ρ meson nucleon scattering amplitude f _ρN extracted from the measurements is used to generate this potential. The calculated e ⁺ e ^? invariant mass distribution spectra are compared with those measured at Jefferson Laboratory. The calculated results for the transparency ratio are also presented.     

On Multiple Scattering of Radiation by an Infinite Grating of Dielectric Circular Cylinders at Oblique Incidence

A rigorous analytical representation for the multiple scattering coefficients of the fields radiated by an infinite grating of dielectric circular cylinders excited by an obliquely incident plane electromagnetic wave is derived in terms of the “well-known scattering coefficients of an isolated dielectric cylinder at oblique incidence” and “Schl?milch series”. In addition, a generalized sum-integral grating equation is acquired for the multiple scattered amplitude of a cylinder at oblique incidence in the grating in terms of the scattering coefficients of the insulating dielectric circular cylinder at oblique incidence.      

On the radiative decays of pions

A critical analysis of the theory of the radiative decays π → ?νγ (?: electron or muon) is given. Earlier results are corrected through a consistent application of gauge invariance and low-energy theorems. Predictions of specific models for the axial-vector form factor are discussed. The paper concludes with remarks on the relate$\text{π →}\text{e}\text{ν}\text{e}\text{e}$.     

Polarization fluctuations in regions bounded by equi-potentials

It is shown that the integral of <{P(rτ), P(r')}>· n? as a function of r over a volume V_e bounded by an equi-potential is independent of r' and of V_e and is determined solely by [?(ω)?1] · n? provided the dielectric constant is local and that V_e is of macroscopic dimensions.     

The interplay of gate potential ande–escattering in surface superlattices

Transport measurements were performed on surface superlattices, formed by a grating gate on a two-dimensional electron gas. We find a suppression of the differential conductance with increasing electric fields, on a scale of a few V cm⁻¹. Even more remarkable is a strong suppression of conductance with increasing temperatureT, where theT-dependence is quadratic. We attribute these observations to electron–electron (e–e) scattering which, in the presence of an external modulated potential, can have a significant influence on the conductance. We also discuss the role of disorder in these systems.     

Crystallographic,optical and magnetic properties of Eu2SiO4

The crystallographic properties of Eu₂SiO₄ are studied in terms of its isomorph Ca₂SiO₄. The recently discovered monoclinic room-temperature phase is ferroelastic and simultaneously ferromagnetic at low temperatures (T _e=5.40°K). The optical absorption and the dispersion properties have been measured in spectral intervals ranging from 0.5 to 3.6 eV and partly for temperatures between 300 and 500°K. This temperature range includes the ferroelastic-paraelastic phase-transition temperature (T _e=438°K). An anomaly of the dielectric constant atT _e suggests the presence of an unstable phase which would be ferroelectric. The Faraday rotation has been measured on either side of the absorption edge at 300 and 77°K. The recent results on crystal structure allow an explanation of the magnetic behaviour of the two ferromagnetic phases known up to now.     

Generalised Tsallis statistics in electron-positron collisions

The scaling of charged hadron fragmentation functions to the Tsallis distribution for the momentum fraction 0.01?x?0.2 is presented for various e⁺e⁻ collision energies. A possible microcanonical generalisation of the Tsallis distribution is proposed, which gives good agreement with measured data up to x≈1. The proposal is based on superstatistics and a Koba-Nielsen-Olesen (KNO) like scaling of multiplicity distributions in e⁺e⁻ experiments.     

Current algebra calculation of e+e-→4π± and determination of ϱ′(1600) parameters

A current algebra calculation of e⁺e^-→4π^± cross section is carried out using the axial current matrix element obtained from τ→π?ν. Assuming ?′→?+2π(I=0, l=0), the following results are obtained: for the A₁ resonance, 1.05?m_A ?1.15 GeV; for ?′, Γ?′(total)≈0.23 GeV, M_?′≈1.5 GeV, Γ(?′→e⁺e^-)≈0.4 keV×B^?1(?′→?′ →?π⁺π).     

Gaussian effective potential for the U(1) Higgs model

In order to investigate the Higgs mechanism nonperturbatively, we compute the Gaussian effective potential of the U(1) Higgs model (“scalar electrodynamics”). We show that the same simple result is obtained in three different formalisms. A general covariant gauge is used, with Landau gauge proving to be optimal. The renormalization generalizes the “autonomous” renormalization for λ?⁴ theory and requires a particular relationship between the bare gauge coupling e _B and the bare scalar self-coupling λ _B. When both couplings are small, then λ is proportional to e⁴ and the scalar/vector mass-squared ratio is of order e², as in the classic 1-loop analysis of Coleman and Weinberg. However, as λ increases, e reaches a maximum value and then decreases, and in this “nonperturbative” regime the Higgs scalar can be much heavier than the vector boson. We compare our results to the autonomously renormalized 1-loop effective potential, finding close agreement in the physical predictions. The main phenomenological implication is a Higgs mass of about 2 TeV.