Effect of Mode Transformation in THz Clinotron

Extension of the theory of a clinotron is developed by use of the scattering matrix of an oversized T-junction on the ends of a slow wave system. The matrix contains elements corresponding to the transformation of slow grating modes into fast ones and vice versa. Those fast waves with low ohmic losses provide strong resonant properties of a clinotron even in the case of strong attenuation of the surface mode. Results of the theoretical simulation are compared with experimental ones and obtained dependencies explain strong resonances in sub-THz clinotrons.     

太赫兹真空源斜注管高频结构研究

斜注管的工作原理是将电子注稍微倾斜于慢波系统表面，通过改变电子注的倾角，来优化有效互作用长度，实现较高的输出功率和效率，可以作为一种新型高功率太赫兹器件。本文就国外的发展情况进行了评述。初步设计了W波段斜注管的几何尺寸和电尺寸，并对其“冷”特性进行了初步研究。     

Hybrid Modes in a Square Corrugated Waveguide

By using two scalar eigenfunctions, electric and magnetic fields in the rectangular (or square) corrugated waveguide are analyzed. In a rectangular corrugated waveguide, the boundary conditions on two corrugated and two smooth walls can be satisfied to excite the hybrid mode. In a highly oversized waveguide where the wavelength of dominant mode is close to that in vacuum, two smooth walls can be exchanged with the corrugated walls because the boundary condition at those walls is satisfied approximately. The replacement is possible due to almost no penetration of the electromagnetic fields into the gap of the replaced walls when the direction of main electric field is parallel to the gap of replaced walls. This characteristic enables us to rotate the polarization of the hybrid mode in the oversized square waveguide with all four corrugated walls and is applicable to the remote steering antenna for electron cyclotron heating in the ITER.     

Excitation of Higher Order Modes in Spherical Cavities

An analysis for determining approximately the optimum position of the exciting source inside a spherical cavity for exciting any TE or TM mode is presented. For any TE or TM mode the orientation of the exciting probe or loop is determined by maximizing the surface integral of /bar H/ or line integral of /bar A/ which is proportional to the excitation coefficient for the corresponding mode. Specific examples of mode discrimination by proper orientation of the exciting source are also included in the paper. Besides, graphs of the surface integral of /bar H/ and the line integral of /bar A/ for various modes are presented to indicate the variation of mutual inductance for any mode, for different positions of the exciting source.     

Excitation and Scattering of Modes on a Dielectric or Optical Fiber

A technique similar to that of Kirchhoff is used to obtain an analytic expression for mode Iaunching on a semi-infinite rod. The approximation is quasi-optical and only valid for small angles of incidence /spl theta/. When /spl theta/ = 0 only HE/sub 1M/ modes are excited; however, for /spl theta/<<1 many modes can be launched. The effect on HE/sub 11/ mode propagation of small imperfections in a dielectric waveguide is analyzed. At the frequency of interest for optical communication (cutoff for the TM/sub 01/ mode) the radiated power is 160 times larger than that scattered into the HE/sub 11/ mode.     

经由受激拉曼绝热过程高效产生太赫兹

论证了在三能级系统中经由受激拉曼绝热过程产生太赫兹,分析了基本模型和泵浦激光与太赫兹产生相干的三能级的理论,并应用在横向激励二氧化碳激光光学泵浦重水分子中,可以产生波长为385μm的太赫兹辐射。产生的太赫兹脉冲功率表现为蒸汽压的函数,并得到了最高太赫兹功率。该技术提供了一种鲁棒性非常好的产生太赫兹的方法。     

经由受激拉曼绝热过程高效产生太赫兹

论证了在三能级系统中经由受激拉曼绝热过程产生太赫兹,分析了基本模型和泵浦激光与太赫兹产生相干的三能级的理论,并应用在横向激励二氧化碳激光光学泵浦重水分子中,可以产生波长为385 μm的太赫兹辐射.产生的太赫兹脉冲功率表现为蒸汽压的函数,并得到了最高太赫兹功率.该技术提供了一种鲁棒性非常好的产生太赫兹的方法.     

Excitation and Scattering of Guided Modes on a Helically Corrugated Dielectric Cylinder

The excitation and scattering of guided modes on a dielectric cylinder with a helical corrugation are investigated. A finite number of radiatiorr modes and an infinite number of surface modes are considered, with the consequence that both the amplitude and phase of the interacting modes can be evaluated. The effect of the pitch angle on the coupling and conversion between the guided modes and the radiation modes of various polarizations is investigated. It is found that TE/sub 0/ guided modes undergo a Brewster phenomenon in the low permittivity dielectrics. The power conservation relation is developed and the reciprocity relations are treated. The aperture fields are used to study the radiation characteristics of a novel dielectric-helix antenna capable of yielding a circularly, elliptically, or linearly polarized radiation.     

Hybrid Modes in Circular Cylindrical Optical Fibers

The classification of hybrid modes in circular cylindrical optical fibers is studied. It is shown that problems of the mode classifications, i.e., the crossover of the dispersion characteristics and the remarkable changes of the polarization states and the field configurations, are caused by the coupling of the HE-type and EH-type modes.     

Mimicking Neuroplasticity in a Hybrid Biopolymer Transistor by Dual Modes Modulation

Neuromorphic computing systems that are capable of parallel information storage and processing with high area and energy efficiencies, offer important opportunities for future storage systems and in‐memory computing. Here, it is shown that a carbon dots/silk protein (CDs/silk) blend can be used as a light‐tunable charge trapping medium to fabricate an electro‐photoactive transistor synapse. The synaptic device can be optically operated in volatile or nonvolatile modes, ensuring concomitant short‐term and long‐term neuroplasticity. The synaptic‐like behaviors are attributed to the photogating effect induced by trapped photogenerated electrons in the hybrid CDs/silk film which is confirmed with atomic force microscopy based electrical techniques. In addition, system‐level pattern recognition capability of the synaptic device is evaluated by a single‐layer perceptron model. The remote optical operation of neuromorphic architecture provides promising building blocks to complete bioinspired photonic computing paradigms.     

Hybrid Modes in Highly Oversized Corrugated Rectangular Waveguides

Using a scattering matrix formalism the relative TE/TM eigenmode contents of hybrid modes in oversized corrugated rectangular waveguides has been calculated. The influences of slot depth and corrugation period on the eigenmode mixture have been examined.     

Coherent Control of Wave Beams Via Unidirectional Evanescent Modes Excitation

Conventional coherent absorption occurs only when two incident beams exhibit mirror symmetry with respect to the absorbing surface, i.e., the two beams have the same incident angles, phases, and amplitudes. This study proposes a more general metasurface paradigm for coherent perfect absorption with impinging waves from arbitrary asymmetric directions. By exploiting excitation of unidirectional evanescent waves, the output can be fixed at one reflection direction for any amplitude and phase of the control wave. It shows theoretically and confirm experimentally that the relative amplitude of the reflected wave can be tuned continuously from zero to unity by changing the phase difference between the two beams, i.e., switching from coherent perfect absorption to full reflection. It hopes that this study will open up promising possibilities for wave manipulation via evanescent waves engineering with applications in optical switches, optical computing, one-side sensing, photovoltaics, and radar cross-section control.     

法拉第手征圆波导中混合模的传输特性

本文研究了法拉第手征圆波导中混合模的传输特性，而在这种双各向异性复杂导波结构中，传输模的横向场分量仍可以用纵向场分量来表示，用Ｍｅｌｌｅｒ求根法分析了不同阶混合模的色散和衰减特征，以及不同本构参数对混合模传播特性的影响。     

W波段斜注管高频结构的设计和注波互作用模拟

斜注管是返波管的一种,其基本原理是将电子注稍微倾斜于慢波结构表面,通过改变电子注的倾角来优化有效互作用长度,达到更高的输出功率和效率.本文论述了斜注管的基本原理,对其冷特性进行了研究,初步设计了W波段斜注管慢波结构,并利用3D电磁模拟软件,对其注-波互作用进行了模拟,模拟得到20W的输出功率以及15GHz的带宽.     

Coupling of Non-Axially Symmetric Hybrid Modes in Dielectric Resonators

A method for the rigorous calculation of the coupling coefficient between dielectric resonators excited in non-axially symmetric hybrid modes is developed. A simplified model is derived which allows approximate accurate calculations of coupling, without solving the detailed boundary value problem. Experimental measurements of the coupling between the two lowest hybrid modes were performed to verify the models, and are found to be in excellent agreement with the calculations.     

Excitation of Hybrid Space-Surface Waves in Clinotrons with Non-uniform Grating

Excitation of surface (slow), space (fast), and hybrid surface-space waves in BWO-clinotron with periodically non-uniform grating has been studied both theoretically and experimentally. It is shown that an interaction of electron beam with hybrid surface-space wave may be more effective than with surface wave because of higher Q-factor, and than with space wave because of higher impedance. The experimental test results of both 100-GHz CW clinotron with non-uniform three-stage grating and of 130-GHz CW clinotron with four-stage grating showed the excitation of radiation with output power more than 1 W and some specific features of electronic frequency tuning.     

New Materials and Structures for Efficient Terahertz (THz) Spectroscopy

Journal of Communications Technology and Electronics - Abstract—The results of developments of materials and structures used for generation and detection of terahertz radiation having applied...     

Vertical-Cavity Surface-Emitting Lasers With Integrated Excitation of Surface Plasmon Polariton Modes

We report the excitation of surface plasmon polaritons (SPPs) on a thin Au layer integrated on top of the mirror of a vertical-cavity surface-emitting laser (VCSEL) along with their subsequent extraction to air. Gratings etched into the Au layer are used to couple the light in to and out of the metal film. The polarization properties of the optical emission from out-coupling gratings placed 5 $mu$ m away from the central optical aperture are used to confirm the coupling of the VCSEL light into and out of the SPP modes. The result paves the way to compact integrated plasmonic devices.      

混合励磁同步电机的技术方案分析

介绍了设计混合励磁同步电机（HESM）时,涉及的主要技术问题及其方案选择,包括原型电机方案、永磁/电励磁磁势串并联关系、励磁结构方案、定转子槽/极匹配原则和谐波抑制方案等。提出了一个励磁绕组位于转子的HESM样机模型,以该模型为例,计算了调磁特性,研究了斜槽方案对谐波抑制的有效性,分析了电励磁对电感的影响,对于HESM电感的非线性,为简化转矩控制的复杂性,宜采用id=0控制。研究了永磁/电励磁比重对调磁特性的影响,以凸极同步发电机为基础,适当增加永磁,设计得到的另一新型HESM,具有较强的励磁能力,且故障发生时可实现有效灭磁。     

High Energy THz Pulse Generation by Tilted Pulse Front Excitation and Its Nonlinear Optical Applications

Generation of high energy THz pulses by tilted pulse front excitation is reviewed. The basic idea and the realized setups are described. Properties of THz pulses generated by using different pump lasers are summarized. Nonlinear optical effects induced by the high energy THz pulses were observed, such as nonlinear refraction, self-phase modulation, saturation of THz absorption, and free carrier generation. The main results on these phenomena are described. The possibility of using THz pulses as a quasi-dc field for increasing the cut-off frequency in high harmonic generation is analyzed. The THz generation setup used in recent experiments is analyzed and arrangements for achieving better THz beam quality and higher THz pulse energy are considered. Finally, some results of calculations indicating significantly increased generation efficiency of 0.2-THz pulses compared to generation efficiency of 1-THz pulses are presented.