摘要:

Photon‐enhanced attachment can be used as a conduction‐control mechanism for diffuse discharge opening switches. This paper presents experimental results on photon‐enhanced attachment based on vibrational excitation of vinyl chloride using a line‐tunable CO2laser. Strong resistance increases and discharge turnoff have been observed in low‐current, externally sustained dc discharges. The influence of experimental parameters such as discharge pressure, attacher concentration, discharge voltage, and laser wavelength are presented.

ISSN:0021-8979    

DOI:10.1063/1.342114

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new microtube target has been adopted for high population inversion of Mg+10ions between 1s3plevel and 1s4por 1s5plevels for the first time. The mechanism for inversion is discussed.

ISSN:0021-8979    

DOI:10.1063/1.342115

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The utility of integral equations to solve eddy current problems has been borne out by numerous computations in the past few years, principally in sinusoidal steady‐state problems. This paper attempts to examine the applicability of the integral approaches in both time and space for the more generic transient problem. The basic formulation for the time space Green’s function approach is laid out. A technique employing Gauss‐Laguerre integration is employed to realize the temporal solution, while Gauss–Legendre integration is used to resolve the spatial field character. The technique is then applied to the fusion electromagnetic induction experiments (FELIX) cylinder experiments in both two and three dimensions. It is found that quite accurate solutions can be obtained using rather coarse time steps and very few unknowns; the three‐dimensional field solution worked out in this context used basically only four unknowns. The solution appears to be somewhat sensitive to the choice of time step, a consequence of a numerical instability imbedded in the Green’s function near the origin.

ISSN:0021-8979    

DOI:10.1063/1.342116

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have developed two strong focusing field configurations that provide high midplane accessibility and therefore are compatible with presently contemplated extraction schemes for high‐current, toroidal accelerators. When these windings are attached to a modified betatron accelerator, the bandwidth of the device is slightly smaller than the bandwidth of a modified betatron with unsplit stellarator windings. However, the bandwidth of the two new configurations is more than sufficient even for modest (20–30 kA) winding currents.

ISSN:0021-8979    

DOI:10.1063/1.342117

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The effects of free‐carrier screening and valence band mixing on gain‐switching characteristics of the field‐effect quantum‐well laser are studied theoretically. Our analysis is based on the multiband effective mass theory and the density matrix formalism with the intraband relaxation taken into account. We calculate the electronic structure of the quantum well by solving simultaneously the multiband effective mass equations for the envelope functions with Poisson’s equation. It is found that the free‐carrier screening affects considerably both electronic properties (band structure and wave functions) and gain‐switching characteristics by reducing the electric field and charge separation in the quantum well when the gate field is applied across the quantum well.

ISSN:0021-8979    

DOI:10.1063/1.342118

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The application of optical thin‐film interference structures, consisting of epitaxial III‐V alloy layers, to the fabrication of optoelectronic devices operating in the 1–10‐&mgr;m wavelength range which are suitable for two‐dimensional array integration and relevant to optical communications and computing is discussed. This paper deals with surface geometry narrow band filters and current injection modulators. Closely related surface lasers will be described in a subsequent publication. An environmentally stable filter consisting of GaAs and AlAs epitaxial layers with a passband width of 1.2 nm at a wavelength of 1.6 &mgr;m is demonstrated. Such filters are found to be tunable by tilting. A proposed design for a surface current injection modulator operating at a wavelength of 1.3 &mgr;m is given with a modulation ratio of 10:1 anticipated for an operating current of 5 mA. The significant advantages of compound semiconductor expitaxial layers over polycrystalline coatings for general thin‐film optics applications are outlined briefly.

ISSN:0021-8979    

DOI:10.1063/1.342119

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Bulk wave reflection formulas are extended to the surface‐wave case, considering Rayleigh and Stoneley waves in terms of refracted inhomogeneous longitudinal and transversal waves, linked by the surface coupling. In this manner, a physical mechanism of second‐harmonic generation process is clearly shown. The analytical expressions and physical pictures of Rayleigh‐ and Stoneley‐wave harmonic generation have been derived in a second‐order approximation. The solution shows that the second‐harmonic surface waves have a field structure different from the fundamental ones and varying with the propagation distance. Some parameters were defined to characterize the elastic surface‐wave second‐harmonic generation efficiency. Numerical data for some isotropic materials are present. The steady‐state form of finite amplitude surface wave is described and explained by a clear physical model.

ISSN:0021-8979    

DOI:10.1063/1.342120

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A three‐dimensional model of the thermocapillary flow within the molten region during laser surface heating is developed. This physically corresponds to the process of a stationary laser beam irradiating on the surface of a moving workpiece. The recirculating flow due to the surface tension gradient is much faster than the scanning motion. This allows a perturbation solution. The basic solution corresponds to the stationary axisymmetric case, and the perturbation is based on a small scanning velocity. The advantage of seeking a perturbation solution is that the three‐dimensional flow is modeled by two sets of two‐dimensional equations which are presumably much more tractable than the original three‐dimensional equations. Numerical solutions are obtained. The solid‐liquid interface is determined by an iterative scheme. In the presence of the recirculating flow, the heat transfer becomes convection dominated. The absorbed laser energy is convected sideways so that a wider and shallower molten region is obtained. The molten pool shape is obtained and presented. The effect of various operation parameters (such as laser power, beam radius) on the pool shape are obtained and discussed. The cooling rate of resolidifying materials is also determined. Trajectory of a fluid particle is presented. This provides the most realistic scenario of mixing in a laser melted pool obtained to date. This also gives a semiquantitative understanding of the mechanism of solute redistribution. The effect of alloying elements, which may change the temperature dependence to an increasing function, is also considered. A reverse recirculating vortex is obtained and its effect on pool shape is presented and discussed.

ISSN:0021-8979    

DOI:10.1063/1.342121

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A differential equation describing the behavior of an oscillatory vane for flow‐speed measurements is obtained. It differs from the classical equation for an ordinary flow‐direction vane in that it contains a positive feedback term representing the flipovers of the fin. No analytical solution to the equation exists, but an oscillatory vane’s response may be determined to a good approximation by simple calculation of second‐order parameters and by use of a relevant coefficient whose value has been obtained from a numerical solution and is provided here in a table for a variety of vanes. In agreement with experiments, the vane’s oscillation frequency is shown to be directly proportional to flow speed, and furthermore, to have a square‐root dependence on the density of the flowing medium, the physical dimensions of the vane, and the reciprocal of its moment of inertia.

ISSN:0021-8979    

DOI:10.1063/1.342122

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We report novel techniques for the scattering of laser light from plasmas to measure density and temperature. Subnanosecond laser pulses are used with fast optical streak cameras to monitor the dispersed scattered light. The spectra are recorded on photographic film. Time resolution down to 100 ps is obtained and stray light problems are eliminated so that the unshifted scattered light can be observed. The techniques have been used to measure densities in the rangene≊1016–1018cm−3and electron temperatures in the rangeTe≊5–35 eV with an accuracy of better than 10%. Laser pulses at 5265 A˚ with an energy of about 10 J are used and give little plasma heating.

ISSN:0021-8979    

DOI:10.1063/1.342099

出版商:AIP    

年代:1988

数据来源: AIP