摘要:

A spherical reflector illuminated by a point source is found to be capable of launching an electromagnetic missile. Since the surfaces of the reflector are not complete spherical surfaces, the problem cannot be solved by simple boundary matching. The electromagnetic fields have to be solved in three regions separately. The general solutions are matched on the boundaries to obtain a set of coefficient equations. Under the conditions for an electromagnetic missile, the coefficient equations are solved asymptotically. The evaluation of the Poynting vector shows that the energy radiated from the reflector has the same slow rate of decay as for the spherical lens.

ISSN:0021-8979    

DOI:10.1063/1.347115

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

3‐methyl‐4‐nitropyridine‐1‐oxide is an organic material presenting high optical nonlinear behavior especially for second‐harmonic generation. Single crystals are obtained by spontaneous nucleation and grown by slow cooling in tetramethoxysilane gel. Coupled phase‐matched second‐harmonic generation and x‐ray topography experiments allow one to relate nonlinear optical performance to crystalline quality.

ISSN:0021-8979    

DOI:10.1063/1.347075

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Degradation studies with over 235 000 device hours have been performed on single‐quantum‐well AlGaAs lasers with uncoated and half‐wavelength Al2O3‐coated facets at stress levels ranging from below threshold up to optical power densities of 23 mW per &mgr;m facet width. The effectiveness of facet protection has been investigated with respect to gradual degradation and catastrophic failures. Facet protection is very important for obtaining long lifetimes and improved immunity to sudden catastrophic failures. With facet coatings, degradation rates as low as 0.18%/kh have been measured at 30 mW in single‐lateral‐mode operation and at 50 °C.

ISSN:0021-8979    

DOI:10.1063/1.347107

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this article we derive several results concerning diffraction from random surface configurations. First, we describe a practical method for inverting diffraction data in order to obtain an explicit expression for the size distribution of diffracting islands on a substrate. The principle of maximum entropy is used to fix the distribution in the formP=exp[−F(A)], whereF(A) is a polynomial in the island areaA. Then we show that the most general use of the maximum entropy principle requires thatFfor the exact size distribution be a simple, linear function of the geometry of the scatterers. While this result is of considerable practical use, of greater importance is the fact that it puts distinct and well‐defined limits on the possible functional form thatP(A) may exhibit. An example calculation is made using our diffraction data for indium on gallium arsenide.

ISSN:0021-8979    

DOI:10.1063/1.347120

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The sequence of stages during precipitation of semiconductor (e.g., CdS, CdSe) clusters from supersaturated glasses exhibiting quantum‐confinement effects was investigated. The rate of formation of nanometer‐size ‘‘quantum dots’’ distributed in a continuous glass matrix is critically determined by the time and temperature of the heat treatment given to the quenched glasses. The entire precipitation process was analyzed in terms of several decomposition stages: nucleation, normal growth, coalescence of quantum dots, and devitrification of the glass matrix itself. Experimental data obtained by differential thermal analysis were utilized to identify the heat‐treatment temperature range associated with the precipitation stages. The size distribution of CdSe quantum‐dot clusters was analyzed using our transmission electron microscopy data. The data of Ekimovetal. [Solid State Commun.56, 921 (1975)] was reduced to time‐temperature master plots useful for precipitating quantum dots of a given size in glasses.

ISSN:0021-8979    

DOI:10.1063/1.347130

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A promising approach for reducing the operating wavelength of x‐ray lasers is the generation of population inversions via recombination in rapidly cooling plasmas. We have examined the relative merits of radiative and hydrodynamic cooling in a freely expanding plasma. The specific lasing scheme studied is recombination in heliumlike silicon, but the general results apply to other elements and ionization stages which are capable of generating gain in the soft x‐ray region. We find that the higher radiative cooling rates obtained by mixing the silicon lasant with a high atomic number coolant are more than offset by the reduced expansion cooling brought on by the higher mass density associated with the high‐Zelements. Specific results are presented for hydrogen, carbon, aluminum, and selenium coolants mixed with silicon lasant. The present results do not apply to magnetically confined lasant plasmas where high‐Zradiators might be valuable.

ISSN:0021-8979    

DOI:10.1063/1.347139

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The complete electroelastic tensor of quartz has been calculated—for the first time—exclusively using the data obtained by the resonator method. Its eight independent components were obtained by the least‐squares fit to 184 observations of the dc‐field‐induced change in the resonance frequency of the extentional mode of rods and thickness modes of plates. Simultaneously, an attempt has been made to calculate the eight independent components of the electrostrictive tensor and the only independent component of the third‐order permittivity tensor of quartz. Only seven values have been obtained here; three of them are linear combinations of these quantities. A comparison made with similar tensors as calculated from the transit‐time experiment [Kittinger, Tichy, and Friedel, J. Appl. Phys.60, 1465 (1986)] yields excellent agreement for the electroelastic tensor. Differences between the corresponding tensor components are comparable with their standard errors. The comparisons available for the electrostrictive tensor are considerably less encouraging. No comparison for the third‐order permittivity (disregarded in the analysis of the transit‐time experiment) could be made.

ISSN:0021-8979    

DOI:10.1063/1.347151

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The phenomenon of current drive under the action of radio‐frequency traveling waves into a tokamak is analytically studied by solving the two‐dimensional Fokker‐Planck equation first treated by Fisch. The runaway rate, the number of runaway electrons, the electron current density, and power density are obtained analytically and are compared with the results of one‐dimensional analytic treatment.

ISSN:0021-8979    

DOI:10.1063/1.347152

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The small‐angle x‐ray intensities, scattered by four of the most typical natural coals, are analyzed assuming that coals behave as polydisperse distributions of cubic particles having a layered structure with an interlayer spacing partly dependent on particle sizes. The particle distributions are determined by a rather fast numerical algorithm, and in the considered momentum‐transfer range, they appear independent of the interlayer spacing. The model reproduces quite well only the intensities which are neither particularly structured nor fractal at very small momentum transfers. Micropore, mesopore, and macropore relative sizes are estimated starting from the obtained particle distributions.

ISSN:0021-8979    

DOI:10.1063/1.347093

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Harda‐C:H films have been deposited through electron cyclotron resonance (ECR) microwave plasma decomposition of CH4diluted with H2gas. It has been found that hard diamondlike films could only be produced under a rf‐induced negative self‐bias of the substrate stage. Raman spectra indicate the deposition of two distinct film types: one film type exhibiting well‐defined bands at 1360 and 1580 cm−1(the graphitic D and G bands) and another displaying a broad Raman peak centered at approximately 1500 cm−1. The optical gaps of these films are from 1.0 to 1.6 eV, respectively, with resistivities >1012&OHgr; cm. Variation of the mirror magnetic‐field profile of the ECR system was examined, demonstrating the manipulation of film morphology through the extraction of different ion energies.

ISSN:0021-8979    

DOI:10.1063/1.347094

出版商:AIP    

年代:1990

数据来源: AIP