摘要:

This paper presents a study of spatial hole burning in the carrier concentration distribution of stripe geometry InGaAsP/InP double heterojunction lasers emitting at 1.3 &mgr;m. To study the behavior in detail we took the mutual relationships between the current flow in the resistive layer, the junction voltages between the active and confining layers, and the carrier concentration distribution in the active layer into consideration. Moreover, we treated the InP/InGaAsP/InP double heterojunction through an analysis of the heterojunction energy band structure. The analysis demonstrated that in narrow‐stripe lasers (?7‐&mgr;m stripe width) spatial hole burning in the carrier concentration distribution is greatly suppressed even at twice the threshold. We found the existence of a self‐focusing current flowing into the center of the stripe that acted to suppress spatial hole burning. The results suggest that in the quaternary lasers—the property of the active layer crystal, for example—long intraband relaxation time contributes greatly to the longitudinal‐mode behavior.

ISSN:0021-8979    

DOI:10.1063/1.331160

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Any recording mechanism which produces a high‐reflectivity spot by disrupting the interference condition which results in the initially low reflectivity of the trilayer structure is a potential mode of recording and data storage. Experimental results are presented for deep pit and bubble modes of recording. In the deep pit mode both the absorber and dielectric layers are melted so that the pit penetrates to the reflector layer. In the bubble mode, outgassing of the dielectric layer results in a micron‐sized raised blister or bubble in the absorber layer. The bubble mode, in particular, offers the potential for high sensitivity and high SNR recording characteristics without the use of low melting point absorber layer materials.

ISSN:0021-8979    

DOI:10.1063/1.331161

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An optimization of channeled substrate narrow stripe GaAs/GaAlAs lasers for operation in the zero‐order transverse mode to output powers of 10 mW is described. A correlation between zero‐order mode power and substrate‐induced optical loss is demonstrated. The devices fabricated have threshold currents around 30 mA, highly linear transfer characteristics, and exhibit quasisingle longitudinal mode behavior. Transient response measurements show device suitability forGbit/s optical communication systems. Preliminary lifetest results indicate a median life of over 10 000 h at 70 °C and 2‐mW output. A computer model of liquid phase epitaxial growth over channels and a theoretical analysis of the waveguide structure grown show good agreement with experiment.

ISSN:0021-8979    

DOI:10.1063/1.331162

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An ultrasonic technique is described that allows the determination of the through‐thickness dimension and limited localization of planar defects (cracks) in an isotropic metal plate. The scattering of horizontally polarized shear (SH) plate waves by edge and buried planar defects is investigated using a variational integral expression. Numerical results are presented that allow the calculation of the SH plate wave signal amplitudes as a function of defect through‐thickness dimension and location within a plate for two‐dimensional cracks. It is shown that SH waves are particularly useful for detecting and sizing of crack‐like defects. In addition, it is demonstrated that in plates, which can support a number of propagating SH plate waves, it is also possible to determine the relative position of a defect from interference phenomena. The numerical results are confirmed experimentally using an electromagnetic‐acoustic transducer system to generate and detect 454‐kHz SH wave signals along the normal to the circumference of a 1.22‐m‐diam steel pipe with a 15.9‐mm wall thickness. The experimental results demonstrate the efficacy of using SH wave signals in quantitative nondestructive evaluation of butt welds.

ISSN:0021-8979    

DOI:10.1063/1.331163

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A variational solution is obtained for scattering of horizontally polarized shear (SH) waves from cracks in plates. The solution permits a trial function for the displacement jump across the crack in the form of a series with arbitrary coefficients to be inserted in the variational expression for the scattering coefficients. This multiple term variational solution is preferable to one‐term solutions when increased accuracy is desired or when the form of the displacement jump across the crack is not apparent. Numerical results are presented for scattering from edge cracks in plates.

ISSN:0021-8979    

DOI:10.1063/1.331164

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The dynamics of dilatation has been investigated for variable density flows which exhibit a temporal evolutionary character. In lieu of decomposing the conservation of mass equation (appropriate for strictly nondiffusive/incompressible flows) and utilizing div u = 0 to generate a Poisson pressure equation, the closure relation ’’small div u’’ was used. This suggests an approximate decomposition of the div u governing equation into a steady elliptic pressure equation and a time‐dependent equation for nonacoustic waves which governs div u (herein denoted by &OHgr;˜): (∂&OHgr;˜/∂&tgr;)−[1+∫&OHgr;˜dx˜−(1/4 Re)(∂ ln&rgr;˜/∂x˜)](∂&OHgr;˜/∂x)=&OHgr;˜2+(1/Re)(∂2&OHgr;˜/∂&OHgr;˜2), utilizing the exact equations of continuity and momentum. The solution of this (’’vorticity‐like’’) equation provides information on how an initially small div u field evolves, frequently into a solitary wave. Should the dilatation remain ’’small,’’ rather than be (nonphysically) forced equal to zero, the full conservation relations may be utilized. However, if div u grows large, the elliptic pressure equation is inconsistent with the untampered governing equations. The motivation for this approach is to provide a structure within which: (1) small diffusive/compressibility effects may be studied, (2) the significance of div u physics, in flows which are traditionally treated as approximately dilatation free, may be analyzed, and (3) evolutionary pressure transport formalisms may be developed and evaluated for computational efficiency/accuracy and the inclusion of nonlinear acoustic waves.

ISSN:0021-8979    

DOI:10.1063/1.331165

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The vibrational population distribution for hydrogen molecules in a hydrogen discharge has been calculated taking into account electron collisional excitation, molecule‐molecule, and wall collisional de‐excitation processes. Electronic excitation processes include vibrational excitation by 1 eV thermal electrons acting through the intermediary of the negative ion resonances, and vibrational excitation caused by the radiative decay of higher singlet electronic states excited by a small population of 60 eV electrons in the discharge. The molecules are de‐excited by molecular collisions transferring vibrational energy into translational energy, and by wall collisions. The distributions exhibit a plateau, or hump, in the central portion of the spectrum. The relative concentration of negative ions is calculated assuming dissociative attachment of the low temperature electrons to vibrationally excited, non‐rotating molecules. The ratio of negative ions to electrons in the discharge is calculated to be of order 1% if the vibrational excitation survives no more than one wall collision, and of order 10% if the excitation survives ten collisions. The possibility is considered that the higher concentrations can be achieved with few wall collisions provided dissociative attachment occurs to highly rotating molecules.

ISSN:0021-8979    

DOI:10.1063/1.331166

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Cylindrical high pressure mercury discharge lamps were operated on a sinusoidal supply voltage at frequencies in the vicinity of their fundamental longitudinal acoustic resonance band. The sound spectrum emitted from the lamp allows the detection of pressure waves in the lamp gas volume. With this method it is shown that there are acoustic resonances which are not combined with visual arc instabilities. In this case the influence of the acoustic resonance on arc and wall temperature profiles was measured. The experimental results can be explained by an additional axial heat flow caused by the acoustic pressure waves.

ISSN:0021-8979    

DOI:10.1063/1.331167

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The fast luminous pulses experimentally observed to propagate in electrical discharge channels, and believed to have a significant role in the process of electrical breakdown, are investigated, using a plasma fluid approach. These pulses fall in two regimes characterized by different average velocities of 106and 108m/s. We concentrate on the lower velocity pulses. A nondimensional analysis is used to show that these waves can be considered as longitudinal electron fluid waves driven by electron pressure gradients in weakly ionized plasmas. Model equations are derived considering each additional term in the momentum equation as a small but finite perturbation. In all cases, standard nonlinear fluid model equations are obtained as possible solutions. Electric forces lead to the Korteweg‐deVries equation, viscosity to Burgers equation, and electron‐neutral collisions to a damped wave equation. The propagation and attenuation of fluid waves along preionized channels is naturally associated with the formation of steps. It is suggested that thermalization must be associated with the injection of electrons from a source external to those in the preionized channel.

ISSN:0021-8979    

DOI:10.1063/1.331168

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

In this paper, a description of a new method for obtaining a strongly nonlinear analytic model for nonlinear electron devices is given. Specific examples include crossed‐field amplifiers and gyro‐travelling wave tubes. This method is an extension of previous work where a nonlinear partial differential equation is derived and reduced by a multiple time scales perturbation technique to a nonlinear Schrodinger equation. The extension of the above approach to a strongly nonlinear regime is accomplished by includingErfxB0(rf electric and dc magnetic field) effects in the linear dispersion relation in an approximate manner. The inclusion of theseErfxB0terms results in nonlinear coefficients (i.e., dependence uponErf) of the nonlinear Schrodinger equation. The importance of these rf related terms is discussed for the crossed‐field amplifier and the gyro‐travelling wave tube.

ISSN:0021-8979    

DOI:10.1063/1.331169

出版商:AIP    

年代:1982

数据来源: AIP