摘要:

A formalism is developed for computing negative conductivities for inverted populations involving impurity states in semiconductors. General expressions are obtained for three classes of systems: class (1), transitions between states belonging to the same band edge; class (2), direct transitions between states belonging to two different band edges; and class (3), indirect transitions between states belonging to two different band edges. The expressions for negative conductivities are simplified by using the effective mass approximation. The results are then applied to an example of each of the three classes of processes. Class (2) is represented by a model of the GaAs diode laser. It is concluded for this model that at low temperatures, with an acceptor concentrationNa∼1018/cc, and an effective acceptor radius ofa∼20 Å, population inversion of donor states relative to acceptor states yields a greater negative conductivity than inversion of donor states relative to the valence band. A brief discussion is presented of the threshold conditions for diode lasers.

ISSN:0021-8979    

DOI:10.1063/1.1713716

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Pulse propagation in maser‐type traveling‐wave amplifiers with a homogeneously broadened transition is treated by a formalism analogous to the Bloch equations. Phenomenological dephasing (T2) and recovery (T1) times are defined, and a linear (nonsaturable) loss mechanism is included. In the numerical calculations, only the case of negligible excitation during the time it takes a pulse to pass is considered. When pulses are allowed to grow until the amplifier is ``saturated,'' steady‐state pulses having a unique shape and intensity independent of the initial pulse are found. The parameters of these steady‐state pulses depend only on the ratio of the linear loss and gain coefficients. Steady‐state pulses have a peak intensity that decreases monotonically from infinity to zero as the linear loss coefficient varies from zero to the gain coefficient, while the pulse width correspondingly varies from zero to infinity, and the pulse energy varies from afinitevalue to zero. Steady‐state pulses propogate at a velocity less than that of the small signal velocity in the medium.

ISSN:0021-8979    

DOI:10.1063/1.1713717

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Polycrystalline copper and silver have been sputtered by 30–170 keV singly ionized argon at various beam angles, and total yields (atoms/ion) have been measured as a function of energy and incident angle. Angular distributions of sputtered material about the target normal indicate a distribution approximately proportional to the cosine of the angle of emission, but with more material collected in the normal direction than for a strict cosine distribution. No significant variation of angular distribution with ion energy or with sputtering beam angle was observed. The yield appears to be independent of pressure, collector temperature, current, and current density. Erratic results were obtained when the target was not water cooled, and when the glass collector plates were not initially coated with a thin layer (∼50 Å) of evaporated metal.

ISSN:0021-8979    

DOI:10.1063/1.1713718

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Laser amplifiers when pumped to a significant degree of population inversion undergo decay via (1) natural spontaneous emission of radiation from individual excited atoms, and (2) a size‐dependent decay due to self‐amplification of the spontaneously emitted radiation which passes through a large fraction of the amplifier length before escaping. This latter effect has a definite size threshold near which the decay rate changes several orders of magnitude. The decay rate is roughly independent of size except near the threshold.

ISSN:0021-8979    

DOI:10.1063/1.1713719

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The equations for the pulsed Townsend discharge involving two ions interacting through the &ggr; process have been solved for the ion densities as a function of time and position. The same mathematical approach yields equations for the single ion case, with or without diffusion, which are valid for all time. Negative ions are a special case in which &ggr;=0. Plots are presented of the rate of ion arrival at the electrode and of ion current, both of which are experimentally accessible. The temporal increase of ion flux in the neighborhood of Townsend's breakdown condition is shown.

ISSN:0021-8979    

DOI:10.1063/1.1713720

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Part I. First‐order theory of fields with an axis and a plane of symmetry. By using a symmetry property of the ion orbits in magnetic or electric fields with rotational symmetry, the ion optics inside these fields can be simply deduced. The physical meaning of the various terms in the expressions for the ion orbits is clarified. First‐order imaging properties are derived.Part II. First‐order theory for the general case. The calculations on the ion optics of fields with an axis and a plane of symmetry are generalized by omitting the requirement of the symmetry plane. The trajectories in the field are calculated up to the second order. The general equation of the ion path is given byr−R=&Sgr; akl cos[k(&agr;w+[open phi])+l(&ggr;w+&psgr;)]z=&Sgr; ckl cos[k(&agr;w+[open phi])+l(&ggr;w+&psgr;)].The first‐order imaging properties are discussed.Part III. Second‐order theory of configurations of consecutive fields and the principle of object aberrations. The method is extended to calculate the ion paths up to the second order in instruments having one or more fields with a plane and an axis of symmetry. By introducing the concept of optical aberrations in the object, the calculation of higher‐order aberrations can be simplified to a large extent.

ISSN:0021-8979    

DOI:10.1063/1.1713721

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The theory of current collection of a moving cylindrical probe is investigated. Volt‐ampere relations are derived for two distinct cases: (i) The general‐ion current for accelerating collector potential and its special cases, including general‐ion current to the stationary probe, orbital‐motion‐limited current to the moving and the stationary probes, and sheath‐area‐limited current to the moving and the stationary probes; (ii) the general‐electron current for the retarding collector potential and its special cases, including general‐electron current to the stationary probe and random‐electron current to the moving and the stationary probes. Orientation of the cylinder with respect to the drift velocity vector is taken into account. Volt‐ampere characteristics are included for illustrating the functional behavior of the current relations.

ISSN:0021-8979    

DOI:10.1063/1.1713722

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Borate glasses doped with Nd3+have been prepared in small (70 g) batches, and rods of sufficiently high optical quality for laser oscillations have been pulled directly from the melts. Laser action occurs in three groups of wavelengths, the strongest emission being at 0.918, 1.057, and 1.401 &mgr;. Plots of the threshold for oscillation at 1.057 &mgr; are given as a function of both Nd2O3concentration and base glass composition.

ISSN:0021-8979    

DOI:10.1063/1.1713723

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The emission of high‐energy secondary electrons from thin targets of low atomic number has been calculated. The targets are assumed to be bombarded with 25‐MeV electrons, 600‐kVp x rays, and prompt fission gamma radiation. The results give maximum efficiency of high‐energy secondary electron emission of 8% for 25‐MeV electrons, 0.30% for prompt fission gamma radiation, and 0.05% for 600‐kVp x rays.

ISSN:0021-8979    

DOI:10.1063/1.1713724

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Cataphoresis in He‐Ne mixtures was studied spectroscopically and the measurements checked by mass spectroscopy. The pressure was varied from 6 to 90 Torr, the wall temperature from 30° to 500°C, and the current from 10 to 500 mA in quartz tubes of 9.52 and 12.7 mm diameter. The results are compared with the theoretical predictions of Druyvesteyn. Cataphoresis improves with increasing pressure, as predicted, except at pressures above 40 Torr, where the quality of cataphoresis improves only slowly with pressure. The slope of the impurity concentration curve does not change linearly with current from 20–100 mA; it increases with current at very low currents and then becomes independent of current. Because of this discrepancy between theory and experiment, a new empirical equation governing cataphoresis in the region of higher currents is suggested. An increase of temperature markedly decreases the effectiveness of cataphoresis. Increasing the tube diameter and decreasing its length also decreases the effectiveness.In order to check for a possible ``retrograde'' cataphoresis some measurements were made with He as a minor constituent in Ne. Spectroscopic observations at the cathode indicate an enhanced He concentration there (retrograde cataphoresis); mass spectroscopic analysis shows that the cataphoresis, while slight, is still normal. The extreme excitation conditions at the cathode render spectral intensity interpretations difficult if not misleading there.

ISSN:0021-8979    

DOI:10.1063/1.1713725

出版商:AIP    

年代:1964

数据来源: AIP