ANALYSIS OF RECTANGULAR WAVEGUIDE GRATING SLOW-WAVE STRUCTURE WITH THE ARBITRARY SHAPED GROOVES

The rectangular waveguide grating slow-wave structure (SWS) with arbitrary shaped grooves is presented and analyzed in this paper. As an all-metal slow-wave circuit, it has properties that can be used in high-power millimeter-wave or sub-millimeter wave traveling wave tube (TWT). The unified dispersion equation and the expression of coupling impedance are obtained in this paper by means of an approximate field-theory analysis, in which the profile of the groove is approximately replaced by a series of steps and the field continuity at the interface of two neighboring steps together with the field matching conditions at the interface between the groove region and the interaction region are employed. A rectangular groove SWS was manufactured and the cold measurement was made. The experimental data are in good agreement with the numerical calculation. The derived transcendental equations are resolved numerically for four classical structures such as rectangular, dovetail, ladder and cosine. Finally, taking the rectangular waveguide grating SWS with rectangular grooves for example, the influences of physical dimensions on dispersion relation and coupling impedance are discussed.     

Specific features of mode spectrum of planar structures with two-dimensional Bragg corrugation (theory and “cold” experiment)

Electrodynamic properties of two-dimensional-periodic Bragg structures of planar geometry are theoretically analyzed within the framework of the geometrical-optics approximation. Specific features of two-dimensional structures with different profiles, such as two-dimensional sinusoidal and “chess-board” corrugation and corrugation in the form of rectangular grooves, are studied. “Cold” testing of the Bragg structures in frequency ranges of 60 and 75 GHz is performed. The measured frequency dependences of the coefficients of reflection, transmission, and scattering in the transverse direction are in good argeement with the calculations. Existence of high-quality modes near the frequency of exact Bragg resonance is experimentally confirmed.     

侧面泵浦高功率双包层光纤激光器的表面弧形金属槽结构的制作和分析

侧面耦合高功率泵浦光技术是获得高功率稀土光纤激光器的关键技术之一。介绍了一种用于侧面泵浦高功率双包层光纤激光器的表面弧形金属槽结构的制作工艺,并且针对已经实验制作出来的表面连续弧形金属凹槽的侧面耦合结构进行了严格的矢量电磁场理论计算,将120°弧形凹槽等效近似为多层等高不等宽的矩形槽并运用透射矩阵算法对这种近似后的多层矩形结构进行优化设计。这种结构可以用于大功率激光二极管阵列的侧面泵浦中,尤其可用于条形半导体激光器侧面泵浦双包层掺杂光纤,以制作各种大功率稀土光纤激光器。     

The theory of planar Bragg resonators

The reflecting properties of one-dimensional planar Bragg gratings are studied. A coupled resonator model for studying the diffraction of electromagnetic waves in an arbitrarily corrugated waveguide is suggested. It is based on exact relationships that follow from the two-dimensional boundary-value problem stated in terms of the Helmholtz equation. The specific relationships for the rectangular corrugation of the grating-forming plates are presented. The reflection coefficients of the Bragg gratings vs. corrugation length and incident radiation frequency are calculated. An analytical solution for the “narrow” corrugation is obtained.     

矩形波纹过模周期慢波结构色散特性及其单模工作分析

 通过数值模拟，给出了一种求解矩形波纹过模周期慢波结构TM_0n模的色散关系的简便方法；研究了周期慢波系统平均半径、波纹周期、波纹幅度等结构参数对本征模式色散特性的影响；讨论了周期慢波系统中表面波与体积波的存在条件；分析了过模周期慢波系统仍能工作在单模状态下的原因。结果表明，过模周期慢波系统中，当结构参数满足一定条件，且与束电压、束半径匹配，使电子束与TM₀₁模同步点位于π模附近，此时TM₀₁模的总场是表面波，在两种选模机制作用下系统可实现TM₀₁单模工作。     

Propagation characteristics of the laser-generated lower-order lamb waves in one-dimensional periodic thin plates

Using the finite element method (FEM), we study the thermoelastic generation and the transmitted power spectra (TPS) of Laser-generated lower-order Lamb wave mode in an one-dimensional thin aluminum plate engraved by a periodic rectangular grating. The calculation verified that the equally good Lamb waves band gaps can also exist in an one-component periodic structure and the width and location of the band gaps can be regulated by the parameters of the depth of the grooves (h), the ratio of the lattice period to the plate thickness (D/L) and the ratio of the width of the grooves to the lattice period (d/D). Specially, we suggest that Lamb wave band gaps can be substantially enlarged by using multiple periodic systems which consist of several pieces of periodic structure with different D/L.     

Stimulated Cherenkov radiation of a relativistic electron beam moving over a periodically corrugated surface (quasi-optical theory)

The propagation of waves over periodically corrugated surfaces and their excitation by relativistic electron beams are investigated within the framework of a quasi-optical approach. The dispersion equation is derived for normal waves under the assumption of a small (in the scale of the period and wavelength) corrugation depth, based on which two limiting cases are identified. In the first limiting case, the wave frequency is far from the Bragg resonance, and the propagation of waves can be described in terms of the impedance approximation, in which the fundamental spatial harmonic slows down. In the second limiting case realized at frequencies close to the Bragg resonance, the field is represented as two counterpropagating quasi-optical wave beams coupled on a corrugated surface and forming a normal surface wave. When interacting with an electron beam, convective instability, which can be used to realize amplifier regimes, corresponds to the first case, and absolute one, which is applied in surface-wave oscillators, corresponds to the second case. The developed theory is used to determine basic characteristics of amplifier and oscillator schemes: the growth rates, the energy exchange efficiency, and the formation of a self-consistent spatial structure of the radiated field. The practical realization of relativistic submillimeter amplifiers and surface-wave oscillators is shown to hold promise.     

A tunable bragg cavity for an efficient millimeter FEL driven by electrostatic accelerators

A comparison between three possible cavity configurations, the confocal cavity, the ring cavity and the Bragg cavity is presented for a millimeter FEL set within the high voltage head of an electrostatic accelerator. A simple mechnical design to make the Bragg cavity tunable is proposed. The usual theory of the sinusoidal Bragg corrugation, in cylindrical geometry, is extended to the rectangular corrugation and, further, the theory of the Bragg mirror is extended to rectangular geometry. The features of a Bragg mirror in cylindrical and rectangular geometry are compared.     

平面超薄准直器件的参数依赖性

本文设计了一具有高效强指向性的平面超薄人工结构,当平面声波垂直入射到该结构时,若中心狭缝处产生的F-P(Fabry-Perot)共振和两侧类亥姆霍兹凹槽的共振频率耦合时,会产生一具有高度指向性的准直声束。通过对结构两侧的凹槽阵列的作用、凹槽周期D和凹槽数量r的探讨,发现凹槽阵列可将散射声波转换成声表面波,大大提高了透射效率,同时结构的共振频率、声透射率和准直效果和D、r的变化关系不大,说明对该结构准直效应产生影响的是F-P共振频率和类亥姆霍兹共振器共振频率,与布拉格散射无关。这一发现有助于在降低结构尺寸的同时仍保持结构的有效性,为后续指向性器件的应用提供了理论依据。     

具有任意槽的矩形波导栅慢波结构高频特性的研究

将任意形状槽的连续轮廓近似用一系列相连的矩形阶梯近似，利用各阶梯面上导纳的匹配，以及槽与互作用区边界场的连续与匹配条件，获得了具有任意槽的矩形波导栅慢波结构的色散方程和耦合阻抗的表达式，并进行理论上的验证.加工制作了矩形槽波导栅模型，冷测表明理论值与测量值相吻合.分别求解几种特殊槽形矩形波导栅慢波结构的色散特性及耦合阻抗，其中，三角形结构的色散和耦合阻抗均最弱，而倒梯形结构色散最强，耦合阻抗最大. 关键词： 矩形波导栅 任意槽 色散特性 慢波结构     

Guidance of Surface Waves with Dielectric Waveguides Having Finite or Infinite Periodic Corrugations

A planar open dielectric waveguide with periodic rectangular corrugations is investigated in the case that surface wave is guided and propagates normally to the corrugation. Our approximate analysis with the propagation characteristics is to consider a corresponding bounded waveguide problem in which perfect electric or magnetic walls are introduced, and the periodic corrugation is regarded as consisting of step discontinuities connected by a length of uniform slab waveguide. By properly taking into account of both surface modes and only a few non-surface-modes, and using conservation of complex power technique (CCPT) as well as solution selection rule (SSR), we can readily derive propagation characteristics in the Bragg interaction region. The calculated results show an excellent agreement with previously published ones.     

Diffraction grating with rectangular grooves exceeding 80% diffraction efficiency

A novel design for a surface relief grating with rectangular grooves is presented. The first reflected diffraction order shows experimentally 84% diffraction efficiency for a metallic grating. The required binary surface relief can be manufactured by using one single microlithographic fabrication step similar to standard processes in microelectronics. Each period of the grating consists of a subwavelength “minilattice” with a variable duty cycle. A theoretical model of the structure is presented and compared to measurements at 10.6 μm wavelength. Applications ranging from deflectors, polarizing beam splitters, variable attenuators to general diffractive components such as kinoforms for laser beam shaping are proposed.     

Scanning electron microscope resolution: 2. Resolution measurements using structures with a rectangular profile

Different techniques for estimating the resolution of a scanning electron microscope are considered. A method for determining the resolution using reduced standard deviations of the distances between reference points which characterize features of the profile of the test object measured at video signals is proposed. Measurements of the resolution of scanning electron microscopes using test objects that represent slitlike grooves in silicon with a rectangular profile are exemplified.     

水中微小波纹圆柱体声散射低频共振调控

塑料类高分子材料甲基丙烯酸甲酯-亚克力(PMMA)圆柱中亚音速Rayleigh波低频隧穿共振可引起反向散射增强,在低频标准散射体设计等领域具有重要应用价值.提出一种微弱形变的规则波纹表面结构,可实现水中PMMA圆柱反向散射低频共振频率的无源调控.利用微扰法推导了水中微弱形变规则波纹圆柱反向散射低频共振频率偏移的近似解,讨论了波纹微扰系数、周期对规则波纹圆柱共振频率偏移的影响规律.基于Rayleigh波相位匹配方法分析了低频共振频率偏移的机理.研究表明:微弱形变规则波纹圆柱中亚音速Rayleigh波沿微弱形变波纹表面传播,与光滑圆柱体相比,传播路径的改变引起Rayleigh波传播相位变化,导致了Rayleigh波低频共振频率发生偏移.最后开展了微弱形变规则波纹圆柱体声散射特性水池实验,获取了其反向散射共振频率,明显观察到了规则波纹圆柱共振频率偏移现象,与理论预报结果吻合较好.     

Design Method for Optical Waveguide Filters Having Corrugation Structures by Corrugation Width Modulation

A method to design a corrugated optical waveguide filter by modulating the corrugation width profile is proposed. This method is based on combined applications of the Fourier transformation and the F-matrix formalism. The method achieves the spatial profile of the corrugation width required to design a filter with any specified spectral profile of the reflection coefficient. The idea of the technique is that the spatial variation of the effective refractive index can be transformed, with the help of the F-matrix formalism, to variation of the corrugation width while maintaining a constant amplitude of the refractive index variation. Two examples are given applying the technique to the design of optical waveguide filters with reflectivity profiles of two- and four-rejection bands.     

Existence and stability of shock waves in relativistic hydrodynamics with general equation of state

Different forms of criteria for the existence and stability of relativistic shock waves are compared. In case of a single-valued shock adiabat expressed as a function of pressure the requirement of the existence of a shock viscous profile is shown to be most restrictive. This criterion overlaps evolutionarity conditions, the entropy criterion and corrugation stability. The relativistic criterion of the spontaneous radiation of sound is proved to be equivalent to the condition of shock quasi-instability with respect to three-wave branching. The results are qualitatively analogous to those of a non-relativistic consideration.     

Normal-incidence scattering of surface plasmon polaritons by one-dimensional nanoindentations: a multimodal description

In this paper a theoretical study is made on the scattering of surface plasmon polaritons by a finite periodic array of one-dimensional rectangular grooves. Our approach is based on a multimodal expansion technique. We have found that the geometrical parameters of the array can be properly tuned to achieve optimal performance of the structure either as a Bragg reflector or as a converter of surface plasmon polaritons into light. Most importantly, such functionalities can be fully achieved with a relatively small number of grooves. PACS  73.20.Mf; 78.67.-n; 41.20.Jb     

Electromagnetic modeling of near-field phase-shifting contact lithography with broadband ultraviolet illumination

Near-field phase-shifting contact lithography is modeled to characterize electromagnetic absorption in a photoresist layer with one face in contact with a quartz binary phase-shift mask. The broadband ultraviolet illumination is represented as a frequency-spectrum of normally incident plane waves. A rigorous coupled-wave analysis is carried out to determine the absorption spectrum of the photoresist layer. The specific absorption rate in the photoresist layer is calculated and examined in relation to the geometric parameters. Columnar features in the photoresist layer are of higher quality on broadband illumination in contrast to monochromatic illumination, in conformity with some recent experimental results. Feature resolution and profile are noticeably affected by the depth of the grooves in the phase-shift mask. Ideally, the feature linewidth can be less than about 100 nm for broadband illumination in the transverse-magnetic mode. These conclusions are subject to modification by the photochemistry-wavelength characteristics of the photoresist.     

Lamb wave propagation in a plate with a grooved surface with several spatial periodicities

In order to investigate non-destructively the bonding between rough plates, the problem of Lamb waves propagating on a rough plate is addressed in this paper. Numerical analysis is performed on periodical gratings made of identical triangular grooves. If the surface profile is made up of grooves with one periodicity, then a mode conversion is observed. In the wave-number/frequency space, a phonon relation is written between phonons related to the grating and to the incident and reflected-converted modes. If the grooved surface is made up of several spatial periodicities, then the phonon relation is still verified. Signal processing allows us to give an interpretation of the results in the dual space (wave-number/frequency). An experimental study is also performed to corroborate the numerical predictions.