饱和吸收体腔内压缩瞬态同步泵浦锁模光脉冲

用主被动锁模Nd：YAG倍频脉冲序列同步泵浦若丹明染料激光器，在染料激光腔端插入吸收体二乙基噁二碳化青碘化物（DODCI），腔内压缩激光脉冲。在λ=598nm附近，对不同宽度泵浦脉冲均观察到很好的压缩趋势。条纹相机测得的光脉冲明显变得光滑对称。探讨了压缩机理。     

Propagation of optical pulses in a saturable absorber

The coupled Maxwell-Schrodinger equations are used to describe propagation of a pulse in a nonlinear absorbing medium. The absorber is assumed to be comprised of a homogeneously broadened system of two-level atoms that are exactly resonant with the field. Numerical calculations have been performed for incident pulses of hyperbolic-secant shape and of duration that is long compared to the atomic phase-memory time. Selected values of input intensity are considered. For intensities below a certain level the calculations nearly agree with rate-equation predictions, but as the incident intensity is increased we find that optical nutation comes into play. The nutation effect leads to pulse breakup as the packet penetrates into the medium. An analytical calculation, for the case of an applied optical field of step-function form, has been performed in order to provide additional insight about the intensity threshold for nutation.     

一种红外波段多波长吸收器优化设计

本文设计了一种石墨烯/交替光栅/铝(Al)底板结构红外波段电磁超材料多波长吸收器.利用时域有限差分法(FDTD)数值模拟了石墨烯层厚度和光栅结构参数对吸收光谱的影响规律.研究结果证明,基于FP腔共振和相消干涉形成的吸收光谱对石墨烯层厚度和光栅高度较敏感,即随着石墨烯层厚度增大或光栅高度降低,左边频迅速蓝移,伴随各干涉峰...     

Analysis of a wide resonant strip in waveguide

An analysis has been developed to calculate the susceptance due to a wide resonant strip on the transverse plane of a rectangular waveguide. The theory is based upon a variational form for the susceptance, where the current distribution is determined by the moment method. Accurate results have been obtained for the wide strips as confirmed by the measurements     

Negative differential resistance in a resonant quantum wirestructure

It is shown that the transmission characteristics of a semiconductor split-gate device with a double constriction exhibit resonant behavior similar to that in resonant-tunneling diodes (RTDs). The double constriction is modeled with cascaded quantum waveguides of different widths and analyzed by applying a mode-matching technique to the wave function at the discontinuities. At low temperature, the calculated current-voltage characteristics exhibit a region of negative differential resistance. Current-voltage characteristics are presented for different constriction widths and temperatures exhibiting peak-to-valley ratios of up to 4:1 which persist up to temperatures around 10 K     

Fourth harmonic generation in a resonant ring cavity

We have analyzed the generation of the fourth harmonic of pulsed laser radiation in a ring cavity that resonates at the second harmonic wavelength. With the help of numerical simulation, the dependence of the conversion efficiency on input laser power as well as cavity loss and nonlinear crystal coefficient is obtained. The model predicts over 50% conversion from the fundamental to the fourth harmonic with less than 1.2 MW of input power (10 mJ in 8.5 ns). The results compare well with experimental measurements where 39.5% infrared-ultraviolet conversion was obtained using low power from a Q-switched Nd:YAG laser     

Generation in a microstrip-resonator-stabilized double-barrier resonant tunneling structure

Generation in a microstrip-resonator-stabilized double-barrier resonant tunneling structure based on GaAs/AlAs heterostructures has been investigated for the first time. The structures fabricated contain near-contact layers (spacers) that prevent impurities from penetrating into the active part of the structure and improve the temporal characteristics of the system. AuNiGe alloy microstrip contacts, which connect the structure with an external rf circuit, were prepared in a planar implementation, making it possible to minimize the RC delay time in the negative differential conductance region by decreasing the series resistance and capacitance of the structure. In structures with spacer layers, the negative differential conductance exhibits a complex behavior due to the influence of the space charge. Fiz. Tekh. Poluprovodn. 32, 124–127 (January 1998)     

Theoretical study of a Gunn diode in a resonant circuit

A computer simulation of a GaAs Gunn diode in a parallel resonant circuit has been made to determine the optimum device and circuit parameters. The maximum dc to RF efficiency, 5 to 8 percent, is obtained when the product of doping and length is between 10¹²and 2 × 10¹²cm^-2, the product of frequency and length is 10⁷cm/s, and the bias voltage divided by length is 8000 V/cm for a load resistance of30 R_{0}where R0is the low-voltage resistance of the diode. The product of output power and load resistance varies with frequencyfasC f^{2}whereCis 12,000 watt-ohm-GHz²for a load resistance of50 R_{0}. The frequency can be varied over an octave tuning range by the resonant circuit.     

Pulse dispersion in a gyrotropic plasma

The dispersion of nanosecond electromagnetic pulses in a longitudinally magnetized plasma confined in a coaxial transmission line is observed experimentally. The transient response exhibits weakly damped oscillations characteristic of the natural frequencies of a bounded gyrotropic plasma. Measurements of the pulse dispersion caused by reflection from the plasma interface and transmission through the plasma are compared with theoretical results obtained on the basis of a dielectric model of the plasma, in which ion motion and random motions of electrons are neglected.     

光驱动宽频带可调谐太赫兹吸波器设计

设计了一种基于光敏材料硅(Si)的宽频带极化不敏感的光驱动可调谐太赫兹超材料吸波器(metamaterial ab-sorber,简称MMA).该可调谐太赫兹MMA基本单元结构由嵌入光敏硅的紧凑开缝环谐振器结构、中间介质隔离层与金属底板构成.硅的电导率随着入射光的强度而发生改变,从而使太赫兹MMA工作频率和吸波性能得到有效的调节.数值计算结果表明:当硅电导率在1. 0×10~3S/m到5. 0×10~5S/m范围内动态调节时,该MMA吸波特性在0. 442 THz到0. 852 THz范围内动态调节.另外,其相对调节带宽达到63. 37%,吸收率调制深度达到60. 22%.进一步的数值计算结果表明我们所设计的MMA具备极化不敏感和宽入射角的特性.     

Optimum design of a Salisbury screen radar absorber

The author derives expressions for the sheet resistance of a Salisbury screen radar absorber which will yield the maximum bandwidth for a specified level of reflectivity performance, angle of incidence and polarisation. Design curves are also given which relate the maximum absorber bandwidth, reflectivity performance and spacer dielectric constant     

对一种具分形特征的电磁吸波材料的初步分析

研究了一种基于Salisbury屏的微波吸收材料,提出了一种具有Minkowski分形特征、表面加载阻抗的双方环形电磁带隙结构的吸波材料。该种材料具有薄、轻、吸收频带范围宽的优点,且吸波深度深于同等条件下没有分形特征的吸波材料。     

Fundamental investigation on a weakly magnetized ferrite absorber

Investigated are the matching characteristics of a magnetized ferrite absorber, which applies a weakly static magnetic field H_dc perpendicular to the sintered ferrite surface. Applying a static magnetic field to the ferrite enables the matching thickness of the absorber to be reduced from 8 mm in the absence of H_dc to 3 mm under 750 gauss. The matching frequency can also be changed broadly from 0.1 to 0.9 GHz by controlling ferrite thickness and H_dc, simultaneously. These are well explained in terns of an nonsaturated permeability rather than tensor permeability. A thin magnetized ferrite absorber is realized using a ferrite with a large value of imaginary part of permeability when real part takes the value near 1.0. Matching frequency characteristics, whether broad or narrow, correlates closely with the slant of the curve for real part of permeability taking the value near 1.0 in the present frequency     

一种四通道吸收器优化设计研究

本文基于阻抗匹配原理和表面等离子体共振理论,设计了一种石墨烯-MIM结构-金属铝(Al)底板三层结构超材料吸收器.采用时域有限差分法FDTD研究和分析了吸收器的共振吸收光谱,电磁场能量分布,并优化了设计结构.研究结果表明,该吸收器具有近红外波段四个超窄带吸收峰;最大吸收率可达0.943,3 dB带宽均为3.55 μm左...     

谐振式微光学陀螺仪谐振微腔的最新进展

基于Sagnac效应的谐振式微光学陀螺(Resonant Micro-Optical Gyros, RMOG)在集成化、小型化和灵敏度等方面具有巨大潜力,在微纳卫星姿态控制、机器人控制、医学诊断和检测仪器等领域中具有广阔的应用前景,成为近年来研究的热点。谐振微腔作为谐振式微光学陀螺的核心敏感元件,其光学特性与陀螺系统的性能息息相关,谐振腔的研究进展已经严重制约到谐振式微光学陀螺的发展,目前可以通过集成光学技术、微纳光学加工技术和新型材料的应用来减小谐振腔的重量和尺寸,降低成本和功耗,增加系统的可靠性和性能指标。结合期刊会议和相关研究机构披露的信息,简要介绍了谐振式微光学陀螺的发展现状、基本原理以及谐振微腔的特征参量,列举了近期国内外谐振微腔的各种新型结构设计并分析了不同结构的特点与潜力,此外还综述了近期国内外制作谐振微腔的新型材料并总结了不同材料的光学特性,初步探讨了谐振式微光学陀螺敏感单元谐振微腔的后续发展方向和技术发展途径。     

Electric field switching in a resonant tunneling diodeelectroabsorption modulator

The basic mechanism underlying electric field switching produced by a resonant tunneling diode (RTD) is analyzed and the theory compared with experimental results; agreement to within 12% is achieved. The electroabsorption modulator (EAM) device potential of this effect is explored in an optical waveguide configuration. It is shown that a RTD-EAM can provide significant absorption coefficient change, via the Franz-Keldysh effect, at appropriate optical communication wavelengths around 1550 nm and can achieve up to 28-dB optical modulation in a 200-μm active length device. The advantage of the RTD-EAM over the conventional reverse-biased p-n junction EAM, is that the RTD-EAM has, in essence, an integrated electronic amplifier and, therefore, requires considerably less switching power     

嵌入频率选择表面的Salisbury吸波屏设计

在分析传统Salisbury吸波屏的工作原理的基础上,阐述了通过嵌入带损频率选择表面(lossy FSS)来提高吸波性能的可行性,并基于该方案设计了一款能够在3.5~18.5 GHz频率范围内(相对带宽为136%)有效吸波的超宽带吸波结构,这种带损频率选择表面被嵌入在高阻表面(377?/□)和反射面之间。分析了该结构中的附加电阻大小、FSS单元结构和几何尺寸等不同参数对吸波性能的影响,并通过理论分析、计算仿真和实物测量,证实了在厚度相同的情况下,通过加载带损FSS可以使传统Salisbury吸波屏提高约62%的相对带宽,对雷达吸波材料的研发具有一定的指导意义。     

基于W双十字形微结构的太阳能选择性吸收薄膜的数值研究

提出一种基于金属-介质六层膜的高太阳辐射吸收的新型双十字形微结构,计算显示其加权平均吸收率在截止波长前的光谱区约为96.5%,850K温度的辐射率为0.086.通过场图分析对太阳能波段的光热吸收机制进行了探讨.不同入射角情况下的计算结果显示,基于双十字形微结构的太阳能选择性吸收薄膜可具有低偏振依赖性,以及小于50°入射角条件下的低入射角依赖性特点,将能够满足太阳能选择性吸收器件的应用需求.