Carrier energy relaxation time in quantum-well lasers

Carrier energy relaxation via carrier-polar optical phonon interactions with hot phonon effects in multisubband quantum-well structures is theoretically studied by using both bulk longitudinal optical phonons and confined longitudinal optical phonons. We find that the width and the depth of quantum wells only have moderate effects on carrier energy relaxation rates. Our results also indicate that the difference of energy relaxation rates between the quantum well and the bulk material is not significant. We investigate the effects of longitudinal optical phonon lifetimes on the carrier energy relaxation rate. Neglect of the finite decay time of longitudinal optical phonons will significantly underestimate the carrier energy relaxation time; this not only contradicts the experimental results but also severely underestimates the nonlinear gain coefficient due to carrier heating. The implications of our theoretical results in designing high-speed quantum-well lasers are discussed     

The Relationship Between Online Pornography and the Sexual Objectification of Women: The Attenuating Role of Porn Literacy Education

Media literacy interventions partly aim at preventing undesirable media effects at a later point of time. However, longitudinal research on the interaction between media literacy education and media effects is lacking. In this longitudinal study among 1,947 13–25-year-olds, we started to address this lacuna by examining the potential of porn literacy education at schools to attenuate the longitudinal relationship between exposure to sexually explicit Internet material (SEIM) and views of women as sex objects. A two-way interaction effect emerged: The relationship between SEIM and sexist views became weaker, the more users had learned from porn literacy education. No gender or age differences occurred. This study thus provides some first evidence for the role of media education in reducing undesirable media effects.     

Longitudinal sampling and aliasing in spiral CT

Although analyses of in-plane aliasing have been done for conventional computed tomography (CT) images, longitudinal aliasing in spiral CT has not been properly investigated. We propose a mathematical model of the three-dimensional (3-D) sampling scheme in spiral CT and analyze its effects on longitudinal aliasing. We investigated longitudinal aliasing as a function of the helical-interpolation algorithm, pitch, and reconstruction interval using CT simulations and actual phantom scans. Our model predicts, and we verified, that for a radially uniform object at the isocenter, the spiral sampling scheme results in spatially varying cancellation of the aliased spectral islands which, in turn, results in spatially varying longitudinal aliasing. The aliasing is minimal at the scanner isocenter, but worsens with distance from it and rapidly becomes significant. Our results agree with published results observed at the isocenter of the scanner and further provide new insight into the aliasing conditions at off-isocenter locations with respect to the pitch, interpolation algorithm, and reconstruction interval. We conclude that longitudinal aliasing at off-isocenter locations can be significant, and that its magnitude and effects cannot be predicted by measurements made only at the scanner isocenter.     

GaAs外延层掺杂分布的研究

本文讨论了气流的稳定性与外延层纵向浓度分布的关系,不同掺杂的衬底对外延层界面区的影响以及消除不良影响的方法.本文还研究了不同的生长工艺对外延层纵向浓度分布的影响.     

Electromagnetic pulse propagation in a weakly nonlinear plasma

An investigation of the propagation of electromagnetic pulses in a weakly nonlinear, cold, collisionless plasma is described. It is found that a transverse electromagnetic pulse generates, through nonlinear effects, a small amplitude, longitudinal electric pulse field. The transient behavior of this longitudinal electric field is studied. One particular case is considered in detail: the nonlinear generation of a longitudinal electric field by a transverse electromagnetic pulse which is excited by a suddenly turned-on cosinusoidal electric field of frequencyomega_{0}. Computer plots of numerical calculations of the second-order transient longitudinal field are presented.     

考虑纵向磁场的等离子体介质切伦可夫脉塞

在介质切伦可夫脉塞中加入背景等离子体可有效地提高器件的效率和微波输出功率。本文通过求解束-等离子体、内衬介质的波导色散方程,重点分析了纵向均匀磁场对等离子体介质切伦可夫脉塞注波互作用的影响,给出了磁场、等离子体密度、介质参量等对线性空间增长率和能量比的影响曲线。     

声表面波混频谐波的实验观察

基于超声无损检测技术的需要,该文在理论分析声表面波混频效应的基础上,提出了一种混频声表面波的激发方法,并进行了相应的声表面波混频谐波的实验观察研究。设计并制作了以斜入射的体横波和体纵波分别激发声表面波的楔块,通过选择适当的体横、纵波激励信号的周波数及时间延迟,可使斜入射体横、纵波分别激发的声表面波完全混叠。通过对接收到的混叠声表面波时域信号进行脉冲反相处理和傅里叶变换,得到明显的声表面波混频谐波信号。结果表明,借助于楔块两列斜入射的体横、纵波可有效产生混频声表面波,实验观察与理论预期一致,这为发展基于混频声表面波的超声无损检测技术奠定了基础。     

PLASMA-FILLED DIELECTRIC CHERENKOV MASER WITH A LONGITUDINAL MAGNETIC FIELD

The use of a background plasma in a dielectric Cherenkov maser can effectively increase the efficiency and the microwave output power of the device. Here, the effect of the longitudinal uniform magnetic field on the wave-beam interaction of the plasma-filled dielectric Cherenkov maser is examined by solving the beam-plasma, dielectric lined waveguide dispersion equation. And the effects of the longitudinal magnetic field, plasma density and dielectric parameters on the linear spatial growth rate and the energy ratio are presented.     

Global and local effects in gain-coupled multiple-quantum-well DFBlasers

Global and local effects in gain-coupled multiple-quantum-well distributed feedback lasers are analyzed using a new approach that combines a submicrometer two-dimensional analysis together with a longitudinal transfer-matrix calculation. Issues such as complex coupling, the standing wave effect, hole burning, and barrier effects are examined in some detail. It is also shown that, due to the local interactions, the grating contrast is nonuniform along the cavity, leading to the new phenomenon of differential longitudinal spatial hole burning     

Effects of Mechanical Strain on Characteristics of Polycrystalline Silicon Thin-Film Transistors Fabricated on Stainless Steel Foil

The effects of uniaxial tensile strain on the performance of polycrystalline silicon thin-film transistors (poly-Si TFTs) is reported. Longitudinal strain increases the electron mobility and decreases the hole mobility, while transverse strain decreases the electron mobility and slightly decreases the hole mobility. Under longitudinal strain the off current decreases for both NMOS and PMOS TFTs and shifts in threshold voltage and substhreshold slope are observed for p-channel TFTs. A strong dependence on channel length for both electron and hole mobilities under longitudinal strain indicates the presence of a series resistance. For poly-Si TFTs, the mobility changes under strains are related to the strain effects on single crystalline silicon devices.      

Global excess spontaneous emission factor of semiconductor laserswith axially varying characteristics

An expression of the excess spontaneous emission factor of semiconductor lasers having axially varying characteristics has been derived, using a classical treatment for the contribution of spontaneous emission to the laser's noise figure. Although the analysis is focused on semiconductor laser structures, including DFB lasers, the expression obtained can be applied with minor changes to other standing-wave laser geometries. This global excess spontaneous emission factor, accounting for transverse as well as longitudinal effects, is relevant even for laser structures wherein the longitudinal and lateral field distributions are mutually coupled. In this situation, this factor is not equivalent to the product of Petermann's excess noise factor and a longitudinal correction factor accounting for outcoupling losses     

Dynamics of spatial hole burning effects in DFB lasers

A lumped small-signal model for intensity and frequency modulation response of semiconductor lasers, including the effects of longitudinal spatial hole burning (SHB), is presented. It is shown that the laser dynamics including SHB-effects can be accurately described by three small-signal rate equations. The simplicity of the model gives new insight into SHB-effects on modulation response and cavity state stability. It is shown that SHB-effects have a cut-off frequency that depends on the carrier lifetime (including stimulated recombination) and the feedback of perturbations in the longitudinal intensity distribution during modulation     

Finite element solution of electron waveguide discontinuities andits application to quantum field effect directional couplers

A numerical approach based on the finite element method is described for the solution of electron waveguide discontinuities with arbitrary potential and effective-mass distributions. Analytical solutions are introduced for the uniform waveguide regions. The approach is applied to a quantum field effect directional coupler with finite coupling length and longitudinal discontinuities. The effects of the longitudinal interference due to the discontinuities and of the transverse interference due to the even and odd supermodes in the coupling region are studied. The influence of the shape of the wire-tip on the transmission properties is also investigated     

用于高灵敏微磁传感器的LMO膜制备与分析

采用溶胶凝胶法制备了LaMnOx(LMO)薄膜,系统研究了不同烧结温度、纵向直流磁场后退火和生长膜层数对LMO薄膜的巨磁阻抗效应的影响。结果表明,烧结温度、膜的层数以及纵向磁场后退火处理均有效提高了LMO的巨磁阻抗比,其中纵向直流磁场后退火处理提高薄膜阻抗比效果最显著,经过10Oe、400℃恒温1h磁场后退火处理后,在频率5MHz、100Oe外磁场下其磁阻抗比达15.8%,相比未后处理样品磁阻抗比提高了一倍,其对应的磁场灵敏度为0.16%/Oe。同时,实验发现磁场后退火不仅影响薄膜的巨磁阻抗比,也会改变阻抗比极大值所对应的激励频率,这一现象目前仍在探究中。     

Nonlinear gain coefficients in semiconductor lasers: effects ofcarrier heating

Nonlinear gain coefficients due to the effects of carrier heating are derived from the rate equations of carrier energy transfer in semiconductor lasers. We find that, in the modulation responses of semiconductor lasers, stimulated recombination heating will affect the resonant frequency and damping rate in a same form as the effects of spectral hole burning, while free carrier absorption heating will only affect the damping rate. The effects of injection heating and nonstimulated recombination heating are also discussed. The carrier energy relaxation time is calculated from first principles by considering the interactions between carriers and polar optical phonons, deformation potential optical phonons, deformation potential acoustic phonons, piezoelectric acoustic phonons. At the same time, the hot phonon effects associated with the optical phonons are evaluated because their negligible group velocity and finite decay time. We show that the carrier-polar longitudinal optical phonon interaction is the major channel of carrier energy relaxation processes for both electron and holes. We also point out the importance of the longitudinal optical phonon lifetime in evaluating the carrier energy relaxation time. Neglecting the finite decay time of longitudinal optical phonons will significantly underestimate the carrier energy relaxation time, this not only contradicts the experimental results but also severely underestimates the nonlinear gain coefficients due to carrier heating. The effects of spectral hole burning, stimulated recombination heating, and free carrier absorption heating on limiting the modulation bandwidth in semiconductor lasers are also discussed     

Effects of nonlinear gain on single longitudinal mode behavior of semiconductor lasers

The effects of nonlinear gain on the single longitudinal mode are analyzed by means of multilongitudinal mode and multitransverse mode rate equations and compared with the linear gain calculations and experments. It is shown that further suppression of the third order nonlinear gain on nonlasing modes always serves to accelerate the process of the single longitudinal mode operation and that results obtained with long cavity length are entirely contrary to those where only linear gain is considered. The experiments also show that single longitudinal mode lasers with even larger output power can be realized with long cavity length; and, with further proper reduction of the stripe width, single mode (single frequency) operation can be realized. But the results obtained from both gain considerations indicate that single longitudinal mode operation will be facilitated if the active layer is not too thin and the end face reflectivity is increased.     

Experimental observation of asymmetric detuning characteristics in semiconductor laser injection locking

The effects of refractive index dependence on the active region carrier density in semiconductor laser injection locking have been examined experimentally. Strong asymmetry has been observed in the relation between locked longitudinal mode intensity and the difference between an original longitudinal mode wavelength and the injecting light wavelength.     

CLADISS-a longitudinal multimode model for the analysis of thestatic, dynamic, and stochastic behavior of diode lasers withdistributed feedback

A computer model called CLADISS is presented for the analysis of multisection diode lasers. The model allows for the analysis of a wide variety of multisection devices with discrete or distributed internal reflections. The simulator can carry out a threshold, DC, AC, and a noise analysis. The threshold analysis determines the threshold of the various longitudinal modes of the laser. The power versus current and the wavelength versus current characteristics are found with the self-consistent DC analysis. CLADISS includes all of the longitudinal variations by dividing each laser section in many short segments. Both the optical field and carrier density are discretized according to this segmentation. To demonstrate the capabilities of CLADISS some nonlinear effects in DFB lasers are treated. Instabilities induced in the side-mode suppression ratio by spatial hole burning are considered. The effects of spatial hole burning and side modes on the FM response on the linewidth are discussed     

微极广义磁热弹性固体界面上波的传播

给出了微极广义热弹性固体的一般控制方程；研究了在定常磁场作用下具有均匀初始温度的两理想接触微极弹性介质平面分界面上磁热弹性波的传播特性；给出了分别在缺少磁场、热场作用或不同广义热传导理论下反射或折射热波、纵向位移波、耦合横向和微旋转波与入射纵向位移波的振幅比随入射角变化的关系曲线，讨论了热松弛及磁场对振幅比的影响。结果表明：热松弛时间及磁场对振幅比均有显著影响，改变热松弛时间或磁场强度可以明显改变波的传播形式。     

光盘读写头光栅纵向和横向加工误差数值分析

基于标量衍射理论给出了矩形光栅衍射效率的一般表达式,数值分析了VCD、DVD和CD-ROM光盘读写头(光学头)分束光栅纵向和横向加工误差对辅助光束与读写主光束强度之比以及对透过率的影响.结果表明,对辅助光束与读写主光束强度之比,纵向加工误差与横向加工误差可以互补,但是,要以损失部分透过率为代价;对光学头分束光栅,其纵向加工误差与横向加工误差间存在的互补性,对光栅的具体制作有着实际的参考价值.