摘要:

The parabolic variation of saturation ion current with probe potential observed in dense plasmas is fortuitous and is not directly related to the effects of orbital motion. Agreement between measured and computed saturation ion characteristics is illustrated. The discussion is in the framework of collisionless, magnetic‐field‐free theories; they apply to the experiments only if the ion Larmor radius is much larger than the probe radius.

ISSN:0021-8979    

DOI:10.1063/1.1714200

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Measurements of magnetization of polycrystalline EuS powder are obtained by the pyromagnetic method between 4.2° and 60°K in fixed applied fields ranging from 4 to 14 kOe. For fields sufficient to saturate (H0≥12kOe), the data, as analyzed by Weiss molecular field theory with a new graphical technique, specifyTc=16.5°±0.2°K, in good agreement with the specific heat anomaly at 16.2°K. The observed behavior of the approach to saturation suggests a preferred choice of mechanisms for the origin of the large saturation field.

ISSN:0021-8979    

DOI:10.1063/1.1714201

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The electroluminescence of Zn diffused diodes was studied in forward and reverse bias. Emission spectra obtained for forward biasing showed a near‐edge as well as a low‐energy line. In the composition rangex>0.55, where the lowest conduction band minimum is atk=0, most photons are emitted in the near‐edge line. Lasing action could be observed in this range, and the shortest wavelength where stimulated emission was obtained at 77°K was 6380 Å. Forx<0.55, where the lowest conduction band minimum is the (100) minimum, the low‐energy emission becomes dominant. The energy separation between near‐edge and low‐energy line varies between 0.4 and 0.47 eV at 77°K depending on composition. This suggests that the same defect is responsible for the low‐energy emission in all these diodes (including GaAs and GaP). In reverse bias, near‐edge emission and emission at higher energies than bandgap could be observed forx<0.55. The cutoff energy of the emission on the high‐energy side was measured as a function of composition. It was found to vary in a manner similar to the variation of the energy of the (000) conduction band minimum.The external quantum efficiency of the forward bias emission drops sharply by two orders of magnitude at the compositionx=0.55 whenxis decreased. The efficiency of the reverse bias emission is independent of composition.

ISSN:0021-8979    

DOI:10.1063/1.1714202

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A detailed theory is developed for first‐order transverse pumping mechanisms arising from terms in the magnetocrystalline energy which are linear in strain. A physical description of these mechanisms is given in terms of direct and indirect interactions among the particle displacement and magnetization variables, and the instabilities of the medium are classified as direct or indirect according to the mechanisms involved. Numerical values of the thresholds are calculated as a function of propagation angle for longitudinal magnetoelastic instabilities in YIG pumped at 1000 Mc/sec. It is shown that two magnetoelastic instabilities have thresholds which are substantially lower than the second‐order spin‐wave instability threshold. The implications of this result relative to the parametric amplification of elastic waves and the interpretation of certain anomalous saturation effects in ferrites are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714203

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

X‐ray yield in photons/sr/electron was measured for theK&agr; lines of Ti, Cr, Mn, Fe, Cu, Zn, Ge, Zr, and theL&agr; lines of Ta and Au. Incident electron energy was varied from 11 to 38 keV, and for some elements the take‐off angle for emerging x rays was varied from 6 to 45 deg. Theoretical yield values calculated after the method of Metchnik and Tomlin showed an average deviation of about 30% from the measured values, a very satisfactory agreement.Line/background ratios were also measured for the same elements and conditions. Normalization to the natural x‐ray line breadths gave ratios between 100/1 and 26 000/1 depending on the element and experimental conditions. Line/background ratios are consistently larger at low take‐off angles indicating that the characteristic radiation must be generated relatively closer to the surface than the continuum of the same wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1714204

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The behavior of a steady‐state argon arc plasma flowing through a cold 1‐cm circular copper pipe at pressures from 0.1 to 1 atm and gas flow rate of 2600 ml/min is studied by microwave cavity techniques. The high electron density (ne>1016cm−3) and large density gradients in the arc preclude the usual simple interpretation of data. At this density it is however possible to interpret the cavity resonant frequency as a measure of the ``diameter'' of the arc column. Experimental results show the dependence of this diameter on pressure, arc current, and the presence of contaminant gases in concentrations as small as 10 ppm. A simple explanation of the influence of diatomic contaminants is given which attributes column contraction to enhanced thermal conductivity brought about by diffusion of dissociation energy. Dilation of column caused by krypton is attributed to enhanced electron concentration in the cooler regions of the plasma due to krypton's lower ionization potential. Calculations of thermal conductivity of argon‐contaminant mixtures are shown to correlate well with the experimental results. The microwave technique appears in a new role as monitor and judge of the plasma behavior.

ISSN:0021-8979    

DOI:10.1063/1.1714205

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Measurements are reported of the total cross section for deactivation of neon3P2and3P0(2p53s) metastables by inelastic collisions with H2, D2, CH4, and NH3. Observations were conducted by applying the methods of resonance radiation absorption and microwave diagnostics to the afterglow plasma following a weak pulsed discharge in a neon‐hydrogenic impurity mixture. The cross section for3P2deactivation by H2was found to increase from 0.7×10−15cm2at 300°K to 2.5×10−15cm2at 650°K. The cross section for ionization of H2by Ne*3P2collision was found to represent only a fraction of the above. The reaction which dissociates H2and partly converts the metastable energy into H&agr;(6563 Å) light has been observed in H2, D2, CH4, and NH3and may represent a significant contribution to the total deactivation in each case. No H&agr; light was produced as a result of the destruction of a helium3S1metastable by collision with H2.

ISSN:0021-8979    

DOI:10.1063/1.1714206

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Application of an automatic feedback control for long‐term frequency stabilization of a He&sngbnd;Ne optical maser at the center frequency of the atomic resonance is described. The length of the Fabry‐Perot resonator is modulated at a low frequency with small amplitude. The fundamental, second harmonic, and third harmonic components of this modulation frequency in the light output of the maser are used to control the tilt angles of the mirrors, the radio‐frequency excitation power input, and the separation of the mirrors, respectively. The frequency stability is determined by observing the photobeat between the outputs of two independently stabilized masers. Isotopically enriched samples of Ne are used in the two masers with one of them enriched in20Ne and the other in22Ne. The optical output of a maser stabilized in this manner is frequency modulated and the center frequency has been found to be stable to several parts in 1010over very long periods.

ISSN:0021-8979    

DOI:10.1063/1.1714207

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A theory is presented of induced Raman emission in a three‐level system whose parameters are appropriate for microwave to optical frequencies. Solutions of the time‐dependent Schro¨dinger equation are obtained for arbitrary intensity of the pump and signal radiations, which are assumed to be not too many line‐widths off resonance. It is shown how the quantum‐mechanical aspects of the problem may be separated from the statistical‐mechanical aspects, in contrast to the density matrix techniques. The frequency dependence of the Raman emission on the frequency and intensity of the pumping radiation obtained by this method is presented and compared with the results we have obtained by other methods. The intensity and line shape of the Raman emission when the pump frequency is far off resonance are also obtained. The case of three interacting fields is also considered.

ISSN:0021-8979    

DOI:10.1063/1.1714208

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The spacings between the standing spin wave modes excited in Permalloy films, prepared in a high‐vacuum system at pressures near 10−7Torr, are found to obey a quadratic dependence on order number for the magnetic field normal to the plane of the film (H⊥) as well as in the plane of the film (HII). The spacings and intensities of the modes, as a function of the angle &phgr; which the magnetic field makes with respect to the film normal, indicate that the modes are nearly unpinned for &phgr;crit>&phgr;≥90° (HII), are completely unpinned at &phgr;crit, and partially pinned for &phgr;crit>&phgr;≥0° (H⊥). This type of pinning behavior is explained qualitatively by assuming that the films are nearly uniformly magnetized except for a very thin surface layer, of the order of ten lattice spacings, which exhibits a lower magnetization than the bulk. In addition, the observed pinning for the modes suggests that the boundary condition imposed on the transverse component of the magnetization at an air‐ferromagnetic interface is that the normal derivative of the magnetization vanish.It is concluded that ferromagnetic films prepared in high vacuum should be suitable for the determination of physical parameters, such asA/M, the ratio of exchange constant to the saturation magnetization, as their spectra are relatively free from the anomalous features observed in all of the previously reported SSWM investigations. Experimental evidence is presented that these anomalous features are probably due to contamination of the films by both residual gases in the evaporation chamber and by impurities introduced by the vacuum system itself.

ISSN:0021-8979    

DOI:10.1063/1.1714209

出版商:AIP    

年代:1965

数据来源: AIP