摘要:

The effect of the motion of a strongly magnetized and cold plasma on the propagation and radiation of electromagnetic waves is considered. The radiation loss suffered by a finite dipole situated in a moving plasma is calculated. It is shown that when the dipole frequency exceeds the plasma frequency, the total radiation emitted by the dipole can be ehnanced by several orders of magnitude by a slowly moving plasma. The radiation output can also be enhanced when the dipole frequency is less than the plasma frequency, particularly at relativistic speeds, provided the scale length of the dipole is sufficiently large.

ISSN:0021-8979    

DOI:10.1063/1.1709309

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Experimental results obtained on CdS, ZnO, and CdSe are presented which show electron‐beam‐pumped laser emission resulting from the decay of free excitons to photons and longitudinal optical (LO) phonons. Calculations based on available absorption data for ZnO and CdS show that at 77°K the required exciton density for stimulated emission is about 1017and 1018cm−3, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1709310

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The optical quenching spectrum in CdS and ZnS single crystals has been investigated as a function of temperature, using a high‐resolution monochromator and polarized light. The well‐known spectrum in both materials consists of a narrow band with maximum at about 0.9 eV and a broader band with onset at about 1.1 eV. Poorly resolved fine structure was detected in the 0.9 eV band in CdS between 0.83 and 0.92 eV; no fine structure was detected in the higher‐energy band. No fine structure could be detected in the less accurate measurements on ZnS. No polarization effects of any kind were detected in either material. Studies of the temperature dependence of optical quenching confirm the early indications described by Bube, and indicate anew the intrinsically complex nature of the sensitizing center. The problems related to distinguishing between intrinsic‐defect and copper‐impurity effects are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709311

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Theoretical expressions have been derived for the charge‐distribution function and resultant voltage‐decay curve applicable to drift mobility experiments in the presence of traps. The charge‐distribution function was obtained under the assumption of constant electric field and the neglect of recombination and diffusion. The results are, therefore, limited to the case of low carrier densities.The general expression for the voltage‐decay curve is quite complicated, but useful approximations are made for various time regions. In addition, it is shown how the theory may be applied to the xerographic discharge mode under certain limited conditions.

ISSN:0021-8979    

DOI:10.1063/1.1709312

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The reflectance of single crystals of MgO was measured at a 15° angle of incidence for photon energies between 4 and 29 eV and the optical constants obtained by a Kramers‐Kronig analysis of the reflectance data. In the energy range 4–14.5 eV, structure in the reflectance is in good agreement with that already reported. Reflectance measurements have not been previously reported above 14.5 eV. Peaks in the optical conductivity locate the &Ggr; exciton at 7.65 eV and interband transitions at 11.0, 13.2, 14.9, 17.0, ∼19, 20.8, and ∼24 eV. The absorption edge for band‐to‐band transitions is estimated to be at 7.9 eV. The calculated energy‐loss function −Im(&egr;+1)−1, where &egr; is the dielectric constant, shows a maximum at 21.3 eV while the calculated loss function −Im&egr;−1shows a maximum at 22.4 eV and a subsidiary maximum at 25.4 eV. It is suggested that these maxima in −Im&egr;−1correspond to volume plasma resonances involving 6 and 8 electrons per molecule, respectively. The volume plasma energies calculated on the assumption of 6 and 8 free electrons per molecule are 21 and 24 eV, respectively. Use of a sum rule enables us to explain qualitatively the shifts of the plasma resonances from the free electron values. Similarly, the proximity of the peaks in −Im(&egr;+1)−1and −Im&egr;−1, locating surface and volume plasma losses can be explained. These results, from optical measurements, are used to identify characteristic electron energy losses, obtained from the literature, as being due to single‐electron transitions or to collective oscillations.

ISSN:0021-8979    

DOI:10.1063/1.1709313

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper describes the development of an instrument which is analogous to an electron microprobe x‐ray analyzer, whereby the electron microprobe is replaced by an ion microprobe, and the x‐ray spectrometer by a mass spectrometer. A duoplasmatron is the primary ion source. The primary ion beam is mass separated to eliminate impurity ions. A probe diameter of less than 2 &mgr; at 2×10−10A is realized for 12‐kV Ar+ions. A new mass spectrometer was developed with the emphasis on high transmission, yet simple construction. It is stigmatic imaging, double focusing, has a mass‐resolving power of 300 with a solid acceptance angle of 1.5×10−2sr (4° half‐angle) and a transmitted‐energy bandwidth of 10%. It consists of an axially symmetrical electrostatic Einzel lens, a 45° spherical condenser sector, and a magnetic field with plane but inclined pole faces, which deflects the beam by 90°. No entrance slit is used. Experimental results are presented.

ISSN:0021-8979    

DOI:10.1063/1.1709314

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The behavior of partially polarized waves in a homogeneous, dispersive medium with small anisotropy is considered. The field solutions for a medium specified by a tensor permeability are derived from Maxwell's equations. A power coherency matrix and a brightness temperature matrix are defined and discussed. The tensor equivalent to the equation of radiative transfer for an emitting and absorbing medium is derived from a form of Poynting's theorem, and the general solution to this equation for the brightness temperature matrix is given. The assumptions and restrictions employed in the development are reviewed and the effect of relaxing them is discussed. Finally, the method is applied to a simplified version of absorption by Zeeman‐split resonance lines.

ISSN:0021-8979    

DOI:10.1063/1.1709315

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Certain dust particles exhibit steady rectilinear motion when situated in the standing light wave inside a laser cavity. Some observations and a simple theory are presented which show that these particles are oriented by the laser beam. In addition, semiquantitative calculations are given which indicate that the driving force and stabilizing torque are radiometric in origin.

ISSN:0021-8979    

DOI:10.1063/1.1709316

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

General solutions have been obtained for screw, gliding edge, climbing edge, and mixed dislocations traveling with a uniform motion at velocities in the transonic and supersonic velocity range. The motion is considered to occur on planes that give up finite amounts of energy per unit distance of dislocation movement. The only previous work on this problem is Eshelby's general solution of the supersonic screw dislocation and Stroh's and Ang and Williams' work on discrete dislocations that move on planes that give up an infinite amount of energy per unit distance of dislocation movement. The most interesting new result is that the limiting dislocation velocity of an ordinary dislocation pushed by an applied stress lies in the transonic velocity region, not at the shear‐wave velocity as is usually assumed in the literature. Only the screw dislocation is limited by this latter velocity. We have reached the following conclusions: Any dislocation that runs on a plane that gives up energy must move at a supersonic velocity if the force law across the plane never changes sign. A supersonic dislocation, like a subsonic dislocation, can move at an arbitrary velocity. A dislocation that moves on a plane that gives up energy will move in the transonic velocity region if the force law does have a sign reversal. A dislocation that moves in the transonic velocity region cannot move at an arbitrary velocity; it moves at a unique velocity whose value depends on the exact force law.

ISSN:0021-8979    

DOI:10.1063/1.1709317

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Pressure irregularities are shown to be present within the wave front in reacting nitromethane‐acetone solutions. Throughout the test series described, the reaction wave was overdriven, thereby producing reaction in solutions too dilute to detonate in a normal manner. This device served to produce large pressure irregularities which could easily be seen with our optical system. The irregularities in the more dilute nitromethane solutions are several millimeters in lateral extent although quite shallow normal to the wave front. High‐speed photographs are presented which show the irregularities to vary with the nitromethane dilution and with the strength of the initiating shock.

ISSN:0021-8979    

DOI:10.1063/1.1709318

出版商:AIP    

年代:1967

数据来源: AIP