摘要:

We present a model, based on the nonequilibrium retarded Green’s function method of the quantum kinetic (Keldysh) theory, that describes carrier transport in three‐dimensional quantum structures with translational invariance in the transverse direction. The transport equations include inelastic phase‐breaking processes and describe the transport of both the coherent and incoherent electrons within the same framework with a set of first‐order coupled linear differential equations. These equations can be solved without resorting to evaluating the Green’s function. The model accounts for local space charges in Poisson’s equation and is suitable for modeling the steady‐state current‐voltage characteristics of double‐barrier structures. A realistic model for these devices should include the effects of inelastic processes and space charge simultaneously. However, as an illustration, we present numerical results for double‐barrier devices by assuming that the electrons undergo elastic phase‐breaking collisions only. Our simulation results show that the accumulated space charge is a function of phase‐breaking collision and that the presence of dissipation within the contacts is partly responsible for the low observed peak‐to‐valley current ratio.

ISSN:0021-8979    

DOI:10.1063/1.350999

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Dispersion relations are derived to determine the growth rate, dominant wavelength, and group velocity of disturbances caused by the beam breakup instability. Considerations include weak and strong focusing,x‐ycoupling in solenoidal transport, the spacing of accelerator cavities, and periodically pulsed beams. Beam breakup growth is minimum when the cavity spacing equals an integral number of half‐betatron wavelengths for quadrupole focusing, and an integral number of betatron wavelengths for solenoidal focusing. Minimum growth is also found for periodic pulses separated by an integral number of half‐periods of the TM110cavity mode. Expressions for beam breakup growth at the minima are obtained.

ISSN:0021-8979    

DOI:10.1063/1.351000

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

It has been shown recently that when an electromagnetic (EM) missile with an energy decreasing asr−&egr;is incident upon a perfectly conducting plate the reflected energy will decrease asr−&egr;with the same exponent as the incident EM missile. It has also been shown that when the same EM missile is incident upon a perfectly conducting sphere the rate of the reflected energy decay will be proportional tor−(2+&egr;). In this paper we present a generalized study of the backscattering of EM missile by a perfectly conducting target of arbitrary shape. Utilizing the tangent‐plane approximation, we find that the rate of energy decay of the backscattered field of an EM missile whose energy decreases asr−&egr;is proportional tor−&egr;R1R2/(R1+2r)(R2+2r), whereR1andR2are the two principal radii of curvature of the surface at the specular point.

ISSN:0021-8979    

DOI:10.1063/1.351004

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A method for calculating the magnetic fields of volume currents by using point current sources (monopoles) is derived. A model is developed for a point source that is consistent with Maxwell’s equations. An arbitrary arrangement of point sources in a conducting volume is shown to generate no magnetic field outside the conductor if the volume surface coincides with an equipotential surface of the sources. This allows such sources to be added to any problem without affecting the magnetic field, and simplifies the calculation of the magnetic field generated by an arbitrary point source in both spherical and semi‐infinite volume conductors. The magnetic field generated by current monopoles located within these volume conductors is then derived. The formulation greatly simplifies the analysis of the magnetic field generated by higher‐order current sources, notably dipoles, in these volumes.

ISSN:0021-8979    

DOI:10.1063/1.351005

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The injection current and feedback phase of an optically self‐locked laser diode system are controlled simultaneously to the optimum condition by modulating the injection current and using phase sensitive detection. This simple method requires no special devices and techniques. A small modulation index, less than 0.2, was achieved and this method is expected to be applicable in many fields.

ISSN:0021-8979    

DOI:10.1063/1.351006

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Treatments of the three reflector polarizer and polarization control by selective transmission are given. A twist reflector consists of a unidirectionally conducting surface with a parallel, perfectly conducting plane placed behind it. The twist reflector can be used in the development of a device that can rotate the plane of polarization of the incident wave by the rotation of the twist reflector about an axis normal to its surface. The polarization angle of the emerging wave is determined as a function of the orientation angle of the twist reflector. The polarizer design can be modified to enable it to convert the incident linear polarization into either right or left circular polarization.

ISSN:0021-8979    

DOI:10.1063/1.351007

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Implantation of 1‐MeV and 2‐MeV He+in bulk poly‐(methyl methacrylate) (PMMA) leads to the formation of monomode and multimode lightguides in the range of 1012–1014ions/cm2. The waveguide profiles are measured in pure PMMA and in PMMA doped with some wt% of the azo dye Methyl‐Red. Although parts of the dye molecules are destroyed in the implanted region, a residual dye concentration is maintained to obtain photoinduced TRANS‐CIS isomerization, a change between two spatial forms of the molecule, in the guide area. This is demonstrated by switching the coupling intensity of the guided light by an exposure to blue light in the coupling zone of a prism coupler.

ISSN:0021-8979    

DOI:10.1063/1.350974

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This article describes a novel preionization technique, negative ion assisted preionization (NIAP), in which electrons liberated from a reservoir of negative halide ions by photoionization are used to provide preionization for excimer lasers. The NIAP technique is shown to be capable of greatly reducing the technologically demanding requirements associated with conventional flash preionizers, a factor of particular importance for the high average power laser systems currently under development. The efficiency of the NIAP scheme is described with reference to both experimental measurements of the ion reservoir lifetime, which are found to agree with theoretical models, and to theoretical predictions of the electron liberation efficiency, which are found to differ significantly from some previous treatments. The wide range of possible implementations of the NIAP technique is split into three operational regimes that have quite different characteristics. The benefits of improved preionization control and reduced ionization source intensity requirements are described for each regime. The practical limitations of the technique are discussed, and two experimental demonstrations are presented.

ISSN:0021-8979    

DOI:10.1063/1.350978

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new approach for probing acoustic field in acousto‐optical devices based on dynamical x‐ray diffraction is demonstrated. The measurements were carried out on the ZnO‐SiO2‐Si system. The experimental results as well as the advantages of the method are discussed.

ISSN:0021-8979    

DOI:10.1063/1.350979

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Analytical expressions are derived for the photothermal signal, as the probe beam explores the thermal wave generated by the pump beam in the sample, grazing along its surface at a distancexfrom the heating spot. The relation between the phase of the signal and the thermal wavelength &lgr;this pointed out, providing an analytical foundation to a refined photothermal technique for measuring the thermal diffusivity &agr;. In particular, the analysis shows that both &lgr;thand &agr; can be measured using arbitrary phase shifts relative to the heating spot center, which improves the measurement accuracy and the resolution in the application of this technique to imaging.

ISSN:0021-8979    

DOI:10.1063/1.350980

出版商:AIP    

年代:1992

数据来源: AIP