摘要:

In aiming at an electronic superlattice, epitaxial structures consisting of alternating layers of GaAs and GaAlAs have been grown by molecular‐beam evaporation. The technique of He‐ion backscattering provides a unique method for the direct and non‐destructive profiling of these structures for superlattice layers of a few hundred angstroms if detailed account is made of the backscattering process. The results of Raman spectroscopy and scanning electron microscopy are shown also to furnish complementary information on compositions and thicknesses, respectively. The three techniques give similar results.

ISSN:0021-8979    

DOI:10.1063/1.1662558

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Reversible memory behavior is reported for an insulated gate structure, in which charge is stored on a polysilicon gate. This gate is floating between layers of silicon dioxide (SiO2) and silicon nitride (Si3N4). The floating gate is charged negatively by hot carrier injection through the SiO2, from an avalanche plasma in the underlying silicon. This charge can then be removed by applying a positive voltage between anexternalgate and the silicon substrate. The positive voltage causes electrons to flow through the nitride layer. Both charge states are remembered when external bias voltages are removed. The importance of circuit configuration during charging is discussed, and improvements of injection efficiency for a favorable configuration are described.

ISSN:0021-8979    

DOI:10.1063/1.1662559

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Several authors have considered the possibility of using stimulated Compton scattering for obtaining laser action. To date, all gain calculations for these devices have assumed an infinite interaction region. The purpose of this paper is to consider the effect of a finite geometry on the gain. We find that in most experimental situations the gain is significantly reduced, to the point where stimulated Compton scattering seems unlikely.

ISSN:0021-8979    

DOI:10.1063/1.1662560

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A theoretical model for mode locking induced by saturable absorbers is presented, employing an unidirectional ring laser cavity. Both the gain and loss media are assumed to be homogeneously broadened two‐level systems, on‐resonance with the radiation field. The loss of the cavity is treated as discrete and is supposed to occur at an equivalent mirror. Laser coupled equations are then derived, employing the density matrix formalism together with Maxwell's equations, using the rotating wave and slowly varying envelope approximations. Time‐invariant solutions of the coupled equations are deduced exactly and mode‐locking regions are predicted by a perturbation method. It is found that a suitable absorber can produce mode locking if the laser parameters are appropriately chosen. Generation of the steady‐state pulses (SSP) by the finite‐difference method shows that relatively short intense pulses can be obtained from a mode‐locked laser. In addition, the theoretical model is extended to account for the possibility that the absorbing medium may be less easily saturated than the gain medium and/or the phase coherence times of the two media are very different. It is pointed out that our model can be a good approximation to a real laser system under certain circumstances. It can also be used as a guide in the search for a suitable absorber for particular laser systems.

ISSN:0021-8979    

DOI:10.1063/1.1662561

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A transition from a symmetric to an asymmetric waveguide can serve as a mode‐ and polarization‐dependent light‐wave coupler. Coupling experiments with an efficiency up to 70% are reported. Furthermore, total reflection occurs at the transition if the angle of incidence of the guided wave exceeds a critical value. Coupling and total reflection are explained, using the concept of the effective refractive index.

ISSN:0021-8979    

DOI:10.1063/1.1662562

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Magneto‐optical methods involving only strip domain patterns are proposed for the measurement of characteristic lengthl, saturation magnetization 4&pgr;Ms, and domain wall energy density &sgr;w, in thin uniaxial magnetic films. Determination oflrequires measurement of film thickness and the spatial period of the strip domain pattern in zero applied field as previously proposed by Fowlis and Copeland, while 4&pgr;Msand &sgr;wfollow from additional measurements ofM/MsvsHas a hysteresis loop. The results of calculations which are necessary to put the methods to use are presented in detail. Experimental results are included which indicate reasonable agreement with other methods currently in use. The present method is of greater accuracy and convenience in certain cases. The effects of finite uniaxial anisotropy are quantitatively considered and shown to change the results by 6% or less for materials of practical interest.

ISSN:0021-8979    

DOI:10.1063/1.1662563

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Details of the magnetization behavior of the pseudobinary system ErCo2&sngbnd;ErAl2at temperatures from 1.6 to about 70 K are presented and compared with previous neutron diffraction experiments. ErCo2shows a first‐order phase transition at 33 K from ferrimagnetic order to paramagnetism. Replacement of Co by Al destroys this unusual feature and initially results in enhanced magnetic exchange with increasing ordering temperatures, although the Co moment is rapidly decreasing due to electron transfer. The moment on Co sites is completely quenched beyond 30 mole% ErAl2. Disordered magnetic components on Er sites which develop in the pseudobinary region and have been identified with neutrons can be partly forced into the field direction, but the saturation values are limited by the anisotropy. The origin of disorder is discussed as being either a consequence of the disorder on crystallographic sites or of the changing valence electron concentration. Differential thermal analysis shows only the onset of magnetic ordering and no signs of subsequent magnetic transitions at lower temperatures (down to 4.2 K) for materials with only partial magnetic order.

ISSN:0021-8979    

DOI:10.1063/1.1662564

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper introduces the possibility of using the metastable persistent‐current quantum states of liquid helium II observed in superleaks as the principal element of an extremely stable gyroscope. It is suggested that combining the advantages of the nondecaying angular momentum inherent in the superleak with the suspension technique devised by Ensley could result in unprecedented stability and accuracy. An idealized system is described and two simple physical situations are analyzed. An interesting effect peculiar to this system is predicted. We find that temperature fluctuations, by transferring angular momentum in and out of the supercurrent state, drive the float containing the superleak into rotation. This rotation depends only on the nature of the fluctuations and the persistent current state. On the basis of the analysis of the simplified system described we conclude that a supercurrent gyroscope is quite feasible with existing technology.

ISSN:0021-8979    

DOI:10.1063/1.1662565

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Another variation in the preparation of MnBi films from double layers of the constituents is reported. The dependence of Faraday and Kerr rotations on both composition and film thickness in these films suggests a model wherein a reacted double layer is made up of four separate layers. The variance in magneto‐optic constants of MnBi reported here and previously is resolved in terms of this model.

ISSN:0021-8979    

DOI:10.1063/1.1662566

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The electrical noise properties of superconducting films in a perpendicular magnetic field have been investigated. Tin films were used and the dominant source of noise was found to be a flux‐flow mechanism. Coherent voltage pulses were also detected in some of these films, but the exact origin of these pulses is unknown.

ISSN:0021-8979    

DOI:10.1063/1.1662567

出版商:AIP    

年代:1973

数据来源: AIP