Use of auger spectroscopy in the evaluation of thermionic cathodes

The ability of Auger spectroscopy to identify chemical species existing on a surface has been used to evaluate the properties of "good" and "poor" impregnated tungsten cathodes used in high-power microwave wave tubes. The surfaces of "good" and "poor" cathodes were studied by means of Auger spectroscopy and work function measurements and the results interpreted to analyze failure modes in cathodes removed from TWT's because of poor emission characteristics. Most of the poor cathodes evaluated in this program were obtained from fabricated electron guns that had been employed and discarded from the 200-W TWT tubes developed for the Communication Technology Satellite (CTS) program. The results of these measurements have shown there are at least two types of failure modes that one observes with poor cathodes. They are 1) chemical contamination of the cathode surface and 2) low partial layer barium coverage of the cathode surface.     

On electron initial velocity distributions of some practical thermionic cathodes

In this paper, electron initial velocity distributions of two kinds of practical thermionic cathodes are studied with the pre-accelerating—post-deaccelerating type retarding field method. The phenomenon of the splitting of electron initial velocity distribution of the oxide coated cathode into spectrum under strong pulse electric field is explained, based on the dynamical surface emission centers theory.     

Activation process-dependent characteristics of novel thermionic oxide cathodes for CRT application

The emission and conductivity characteristics of oxide cathodes depend largely on the activation process. In this paper, the electrical properties of new type of oxide cathodes for cathode ray tube (CRT) application, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes. The influence of the activation process over different durations has been investigated. A temperature of T=1425 K was chosen to be higher than the optimum cathode activation temperature (T=1200 K), and the other temperature of T=1125 K was lower than that. The electron activation energy (E) was found to vary in the range from 0.58 to 2.28 eV for cathodes activated at the higher temperature regime, and from 1.08 to 1.9 eV for those activated at the lower temperature regime. Scanning electron microscopy (SEM) and electron diffraction X-ray (EDX) analyses show a structural phase transformation in the oxide material that was activated at 1125 K for a period of 1-12 hours. The SEM mapping shows a large contamination of Ba in the top layer of oxide material. The activator agents tungsten and aluminum are found to penetrate into the BaO/spl bsol/SrO layer in two different ways.     

MICROCOMPUTERIZED MEASUREMENT AND ANALYSIS OF ELECTRON EMISSION PROPERTIES OF THERMIONIC CATHODES

A microcomputerized measurement system is developed.This system automatically acquiresan I-V characteristic curve in 5 seconds with the accuracy of 0.05％ FSR(full scale range).The Schottkyextrapolation field-free emission,the inflection-point emission,the flection-point emission,the average effec-tive work function.the Richardson work function,the work function distribution at the operation tempera-ture and other important information that reflects properties of cathodes are obtained by this system.The re-sults of analysing four types of cathodes demonstrate that this system is very suitable for measuring the activi-ty changes of the cathode in the processes of activation,ageing,poisoning and life test.It is proved that thissystem can also be used to monitor the actlvity of the cathode in the assembled tube by measuring a gridcontrolled travelling-wave tube.     

阴极为半透明Ce/Au的有机发光二极管

在p型硅基底的阳极上制得的顶出光有机发光器件(TOLEDs)采用Ce(xnm)/Au(15nm)(x:4～16)沉积层作为半透明阴极材料.当有机层NPB(60 nm)/Alq3(60 nm)保持不变时,研究了Ce层厚度对透光度和器件性能的影响.结果表明:沉积层为Ce(11nm)/Au(15nm)的阴极透光度达到46％,...     

Detector-enclosed vertical-cavity surface emitting lasers

The authors report the use of novel monolithic lateral photodetectors surrounding vertical-cavity surface emitting lasers to determine the radiative transition rate and lasing threshold independent from the axial emission. The lateral detector photocurrent increases with increasing laser drive current, even as the axial emission rolls over and terminates. This clearly establishes that laser output is limited by the detuning between the Fabry-Perot cavity resonance and the gain bandwidth with temperature, rather than the temperature dependence of the gain.<>     

High-speed vertical-cavity surface emitting laser

Planar, gain-guided vertical-cavity surface-emitting lasers (VCSELs) with a modulation bandwidth of 14 GHz are described. This bandwidth is reached at a drive current of only 8 mA. The intrinsic bandwidth of these devices is estimated to be greater than 50 GHz. Nonlinear light-current characteristics of these lasers may lead to a high level of nonlinear harmonic distortion of the high-frequency output. It is shown that the relative intensity of the second-harmonic response decreases rapidly at higher drive currents, in agreement with a phenomenological model based on the DC characteristics of the laser     

Analysis of grating surface emitting lasers

An approach to the analysis of grating-coupled semiconductor lasers is presented. It is shown that there are only two resonant solutions when the grating has infinite extent. The solutions are either symmetric or antisymmetric about the center of the longitudinal coordinate system where the antisymmetric solution is nonradiating. The field in the grating layer is expressed in terms of grating eigenfunctions and rigorously matched to the boundary conditions at the waveguide interface. Solutions to the finite-length grating problem are expressed as linear combinations of the infinite-length solutions. It is shown that the two diffraction parameters in the coupled-wave equations are composed of sums and differences of the eigenvalues from the infinite-length problem     

发光二极管表面结构对出光特性的影响

用传输矩阵法模拟计算了AlGaInP发光二极管(LED)不同表面结构的光学特性,用等离子体增强化学气相沉积(PECVD)或磁控溅射掺铟氧化锡(ITO)设备,在带有DBR结构的外延衬底上制备出具有不同表面层结构的LED.通过实验结果对比表明,表面生长λ/4n SiON加λ2n ITO增透膜结构复合增透膜的LED,器件光学性能提高最佳,在20 mA注入电流下,光强和光通量分别达到141.7 mcd和0.4733 lm.比同样结构的无增透膜LED轴向光强和光通量分别提高138%和91%.     

Experimental tube for investigating the emission properties of thermionic cathodes working at high temperatures, heated by parallel electron-beam bombardment

The experimental tube for investigating the emission properties of cathodes working at high temperatures was constructed. Cermet cathodes, in the shape of tablets, were heated by parallel electron beam bombardment. The thermoemission constants of ThO2-Mo cermet cathodes were measured by Richardson's straight line method.     

可调谐垂直腔面发射激光器

近年来国内外在可调谐垂直腔面发射激光器这一研究领域取得了极大的进步。叙述了可调谐垂直腔面发射激光器的结构原理和发展历程,对不同结构的优缺点作了对比介绍,展望了可调谐激光器的发展前景。这种器件在光传输、光互连及光并行信息处理等方面有着良好的应用前景。     

Self-pulsations in vertical-cavity surface emitting lasers

The dynamic characteristics of surface emitting lasers with a saturable absorbing layer are modelled and shown to exhibit self-sustained pulsations up to 10 GHz. A set of coupled rate equations is used to investigate the regions of self-pulsations, and show that there is an optimum position for the absorbing layer within the cavity structure to produce the widest range of pulsation frequencies     

Polarisation control for surface emitting lasers

A polarisation control method for surface emitting lasers is proposed. By preparing high refractive index films on one side of dielectric multilayer reflector walls, a differential loss for orthogonal polarisations can be provided. A GaAlAs-GaAs device was fabricated based on this design and the polarisation control has been demonstrated up to 1.4 times the threshold.<>     

表面光栅垂直腔面发射激光器偏振特性研究

研究了表面光栅结构对垂直腔面发射激光器(VCSEL)的偏振控制作用。引入表面光栅后,对不同刻蚀深度下的偏振相关的镜面损耗进行了仿真,结果表明表面光栅刻蚀深度在44~130 nm范围内均可实现稳定偏振,具有较大的工艺容差。表面光栅VCSEL在基横模工作状态下偏振抑制比(Orthogonal Polarization Suppression Ratio, OPSR)超过20 dB,偏振光谱峰间偏振抑制比达到40 dB,且在多横模状态也实现了有效的偏振控制。为了进一步验证光栅对偏振控制的效果,制作了方向互相垂直的两种表面光栅,具有这两种方向光栅的VCSEL的OPSR均达20 dB以上。测试分析表明表面光栅是VCSEL实现稳定偏振的一种有效手段。     

Analysis of terahertz surface emitting quantum-cascade lasers

An analysis of surface-emitting terahertz quantum-cascade lasers operating at wavelengths near 100 /spl mu/m is presented. The devices use distributed feedback through second-order Bragg metal gratings to generate strong emission of radiation normal to the laser surface. The analysis is based on coupling between the exact Floquet-Bloch eigenmodes of infinite periodic structures in finite length devices. The results show performance of surface-emitting terahertz lasers comparable to edge-emitting devices, with high radiative efficiencies and low threshold gains. Using phase-shifts in the grating, high-quality single-lobe beams in the farfield are obtained.     

Noise parameters of SIS mixers

It has been shown that low-noise receivers can be constructed at millimeter wavelengths by using mixers containing superconducting tunnel junctions as the nonlinear elements. This is possible because of both the low intrinsic noise of these devices and their potential for high conversion gain. Here, the quantum theory of mixing is used to derive the full-noise parameters and small-signal parameters of sinusoidally pumped SIS (superconductor-insulator-superconductor) junctions. These are then put into a form that allows the theory of two-port linear networks to be brought to bear, allowing calculation of such useful parameters as minimum noise temperature, optimum source impedance, available (or exchangeable) gain at minimum noise, and stability factor. These quantities are properties of the pumped junction that do not depend on the source or load impedance, but do depend on the terminations at the image and harmonic sideband frequencies. The harmonic sidebands are taken to be shorted, and the image termination dependence is studied. Numerical results are presented for both ideal (BSC theory) and practical (measured current-voltage characteristic) junctions. The noise parameters of the cascade connection of an SIS mixer and a (noisy) IF amplifier are considered, leading to a specification of the optimum coupling network between the two. It is noted that the SIS mixer is usually not unconditionally stable, but that oscillation can be avoided by careful design of the IF coupling network     

组合式二维列阵面发射半导体激光器

设计出新型二维列阵面发射激光器,获得了室温准连续大于250mW的光功率输出。     

长波长垂直腔面发射激光器

给出了长波长垂直腔面发射激光器的器件结构的发展现状，同时对GaInNAs／GaAs垂直腔面发射激光器进行了详细的介绍。最后，给出了所设计的新型1.3μm GaInNAs/GaAs长波长垂直外腔面发射半导体激光器的结构设计，有源区量子阱由980nm半导体激光二极管进行泵浦。这种器件设计实现了激光二极管泵浦与长波长垂直腔面发射激光器的有机结合，同时具有两者的优点。此外，本文还对器件的阈值特性和光输出功率进行了理论计算。     

Microchip vertical external cavity surface emitting lasers

Monolithic vertical external cavity surface emitting lasers of cavity mode volume <1 mm/sup 3/ have been fabricated in the 850 and 980 nm wavelength range. Pump-limited output power >350 mW in a TEM/sub 00/ mode was obtained at 850 nm. Output power >2.5 W was obtained at 980 nm.     

Two-dimensional surface emitting distributed feedback laser arrays

The demonstration of two-dimensional arrays of surface-emitting distributed feedback lasers is reported. A 30-element array is shown to produce up to 6.8 W of pulsed output power. A 27-element array bonded on a silicon microchannel water-cooled heat sink is shown to produce as much as 3 W of continuous-wave output power. The high continuous wave power is possible due to the low thermal resistance in the p-side down design of the surface-emitting distributed feedback lasers and effective heat extraction by a silicon microchannel heat sink