摘要:

The thermally stimulated current method has been applied to the study of thermally activated depolarization of Mylar thermoelectrets. The band arising from the depolarization is broad and sometimes multistructured. It is, in general, centered at approximately 400°K. The peak current is linear with the applied electric polarizing field up to at least 240 kV cm−1. The linearity is taken as evidence that the polarization is due to dipole orientation.

ISSN:0021-8979    

DOI:10.1063/1.1659157

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The phase diagram of bismuth has been studied from 4.2° to 300°K at pressures up to 50 kbar. Pressure was generated using a piston‐cylinder apparatus with AgCl as the pressure transmitting medium. Phase transitions were detected by observing the accompanying discontinuities in electrical resistance. The phase diagram thus determined is in fair agreement with previously published results of other authors. However, the new low‐temperature phase of bismuth reported by Il'ina and Itskevich was not observed.

ISSN:0021-8979    

DOI:10.1063/1.1659158

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The optical losses of homojunction and heterojunction ``close‐confinement'' GaAs injection lasers fabricated by liquid phase epitaxy have been described in terms of a simple waveguide model. By introducing an (AlGa) As&sngbnd;GaAsp+‐pheterojunction (&Dgr;Eg∼0.1 eV) within ∼2 &mgr; of thep‐njunction, the room‐temperature absorption loss is substantially reduced and the laser efficiency increased. This reduced absorption is due to combination of improved optical waveguiding and reduced absorption in thep+material adjoining the active region. In addition, the laser gain coefficient can be increased in some cases by the addition of a heterojunction with the degree of improvement depending on the electron diffusion length, width, and doping level of the active region. The increased gain coefficient can contribute substantially to the reduced threshold current density of ``close‐confinement'' lasers at room temperature. However, the relative contributions of reduced laser loss and increased gain coefficient to the improved performance depends critically on the details of the laser construction, and no generally valid conclusions can be made applicable to all heterojunction lasers. Values of the exterior differential quantum efficiency of 43% are obtained at 300°K, which means that much of the light internally generated is emitted. Because of the reduced internal loss, the spontaneous exterior efficiency is also greatly increased (a factor of 2–3). State‐of‐the art values of the threshold current density for the optimum structures are 10 000 A/cm2for a cavity length of 20 mils, with values of 8000 A/cm2in exceptional units. A power conversion efficiency at 300°K of 10% has been measured, which agrees with the theoretically predicted value. It is noteworthy that the diode series resistance is comparable in the solution‐grown lasers with and without the heterojunction. The laser behavior has been studied as a function of varying acceptor concentration, donor concentration and bandgap energy discontinuity at thep+‐pinterface. Semiquantitative agreement for the laser loss between theory and experiment at 300° and 77°K is obtained for an active region width of ∼2 &mgr;, using reasonable values of the index‐of‐refraction differences between the various laser regions and free‐carrier absorption.

ISSN:0021-8979    

DOI:10.1063/1.1659159

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Short‐term phenomena taking place in a sealed CO2laser have been treated mass spectrometrically. Their influences upon laser action and life have been examined in detail. Gas heating is observed to be proportional to the input power and in a water‐cooled laser at 250 W input power is &Dgr;T/T=0.24, resulting in the power decrease by the factor 0.72 at the relaxation time of the order of milliseconds. Decomposition of CO2molecules is found to obey the equation CO2&rlhar2;CO+½O2which is always at the equilibrium determined by the discharge parameters. The fraction of decomposed molecules is 60% for dc 10 mA and increases slightly with increasing current. The decrease of oxygen during the discharge is the cause of the long‐term shift of equilibrium, which can be suppressed considerably by initial CO filling. These results have been interpreted in terms of the microscopic theory of chemical physics. The proper features in the decomposition mechanism by the discharge have also been given special considerations.

ISSN:0021-8979    

DOI:10.1063/1.1659160

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The soft x‐ray flux from laser sparks in air at a pressure near 330 Torr has been measured with a three‐channel absorption spectrometer. From these measurements plasma temperatures were inferred. For laser peak‐power levels from 300 to 600 MW and pulse durations from 10 to 25 nsec, the temperatures varied from 40 to 160 eV. Streak camera records were taken of the axial plasma growth. For the shortest laser pulses, the plasma temperatures and luminous front velocities were in near agreement with the predictions of the radiatively supported detonation wave model. As the laser pulse width increased so did the plasma velocity, but not the temperature. These higher‐velocity streak records also showed several slower‐moving luminous fronts behind the faster front. These slower fronts are believed to be detonation waves. Space‐ and time‐resolved x‐ray flux measurements were also made, from which the x rays were found to be associated with the highly luminous plasma and only occurred during laser heating of the plasma.

ISSN:0021-8979    

DOI:10.1063/1.1659161

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The inductive coupling between a Josephson junction and a superconducting stripline is calculated. In the overlapping region they share a superconducting film, the structure having superconducting (S) and insulating layers (I) sandwiched S—I—S—I—S. The coupling arises from the magnetic field penetration through the common superconductor. An equivalent circuit representation is exhibited which has the same modes and coupling as the original system. Using the circuit analog, the power transfer is calculated for several cases of interest: (a) power is radiated outward in the stripline from a biased junction and (b) power is absorbed by the junction from a source coupled to the stripline. The criterion for matching the tunnel junction to the stripline is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659162

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The superconducting resistive critical fieldHrof the bcc region of the Ti&sngbnd;Nb&sngbnd;V ternary system has been studied. Measurements at 4.2°K on cold‐rolled alloys at 10 at.% composition intervals determined thatHrvaried smoothly with composition. A maximum inHroccurred at a valence electron to atom rationof 4.4 for pseudobinaries of the system. The ratio of critical field to transition temperature was found to be a function ofnalone in qualitative accord with the theory for type II superconductors. A criterion for predicting the behavior of similar systems is presented.

ISSN:0021-8979    

DOI:10.1063/1.1659163

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

It is found that the operating lives of Zn‐diffused GaAs electroluminescent diodes depend principally upon the donor concentration. Diodes produced from wafers having 1−2×1018donors/cm3have longer operating lives than diodes produced from wafers having 1−2×1017donors/cm3. To a lesser extent, operating lives depend upon the Zn‐diffusion cycle. Optimum results are obtained by carrying out the diffusion at 750°C for four hours followed at 850°C for 45 min. Apparently there is little or no dependence of operating life upon the donor type (Sn or Si), the crystalline orientation of the wafers, or upon epoxy potting of the wafers. Under continuous operation, light output decreases 5%–10% during the first few hours, and then remains approximately constant thereafter (the maximum test duration was 22 500 h). These diffused diodes are relatively simple to fabricate, have efficiencies of the order of 1% and room temperature risetimes of about 10 nsec.

ISSN:0021-8979    

DOI:10.1063/1.1659164

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The special features of this spectrometer are square wave frequency modulation and thermal detection. The modulation results from switching the microwave source between two eigenfrequencies of the cavity, obtaining pulsed frequency modulation without amplitude modulation in the microwave field. This technique is in many respects superior to the conventional static field modulation and has comparable noise suppression. The thermal detection is based on resistance modulation of a silicon monocrystal plate in contact with the sample and constitutes a very sensitive detection method at low temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1659165

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A magnet or a current‐carrying coil, moving with constant velocity above a conducting plate, will experience magnetic lift and drag forces from the eddy currents induced in the plate. The lift and drag forces are calculated for various coil geometries on the assumption that the conducting plate is thin. For this model, the lift at high speeds approaches the force between the coil and its ``image'' located directly below it, and the drag force falls off as (velocity)−1. The ratio of lift to drag is found to be independent of coil geometry, but the velocity dependence of the lift is greatly affected by the geometry. The ratio of lift to coil weight can be as high as 2000 for a superconducting coil moving at 300 mph at 0.1 m above a conducting plate. The relevance of the calculation to magnetically supported high‐speed vehicles is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659166

出版商:AIP    

年代:1970

数据来源: AIP