摘要:

Self‐enhancement (an increase in diffraction efficiency upon readout with a single laser beam) is reported for iron‐doped LiNbO3holograms which have not been ``fixed'' (crystal heated to 100°C during or after recording). The rate of change for self‐enhancement was observed to be equal to and opposite in sign with the rate of erasure observed in the same crystal at the symmetrical Bragg angle.

ISSN:0021-8979    

DOI:10.1063/1.1662282

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Superconducting V3Ga tapes were produced by fabricating a composite of Cu&sngbnd;Ga alloy and a vanadium core and subsequent heat treatment at 625–‐800°C. The critical current of these composite‐processed (CP) V3Ga tapes was measured at 4.2 K in magnetic fields up to 210 kOe. In CP‐V3Ga tapes, the pronounced ``peak effect'' appears at fields near 170 kOe where a critical‐current densityJcof 1×105A/cm2is obtained. At the ``peak field'',Jcis nearly independent of the thicknessdof the V3Ga layer. On the other hand, at low fieldsJcdecreases markedly with increasing thickness. When the Cu&sngbnd;Ga alloy matrix is supplemented by a small amount of manganese, the peak effect disappears consequently improvingJcat lower fields.

ISSN:0021-8979    

DOI:10.1063/1.1662283

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The work of French and Bishop is compared critically with previous attempts to explain the images of grain boundaries in field‐ion micrographs. It is argued that the assumption that the regions adjacent to a boundary behave as rigid bodies is unrealistic for low‐angle boundaries and dubious for high‐angle boundaries in the light of existing theories and experimental observations. In the absence of relaxation it is difficult to relate stepped spiral contrast in the field‐ion image to dislocations unless they have very wide cores. Combined transmission electron microscopy and field‐ion microscopy can be used to clarify the nature of grain boundary dislocations.

ISSN:0021-8979    

DOI:10.1063/1.1662284

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A recent paper by French and Bishop has discussed the field‐ion contrast from a particular grain boundary configuration as a function of increasing angular misorientation, the images being constructed by computer simulation. Although their boundary configuration was pure tilt about [110], the resulting surface contrast displays apparent tilt andtwistcharacter because of the oblique surface section of the emitter tip chosen to contain the boundary trace. The present paper aims to distinguish the contrast events occurring in such images as a function of this apparent tilt and twist character and to quantify the expected contrast in terms of the ``ring‐matching'' contrast theory proposed by the present authors.

ISSN:0021-8979    

DOI:10.1063/1.1662285

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This communication is a reply to certain questions raised on the use of computer image simulation to study grain boundary contrast in field‐ion microscope (FIM) images. The validity of the rigid lattice assumption is assessed for low‐ and high‐angle grain boundaries. Resolution of grain boundary dislocations, boundary contrast as a function of boundary position, the difference in contrast in the FIM between coincidence and off‐coincidence grain boundaries, and the priority of contrast events are discussed. A plane matching method used in transmission electron microscopy is introduced to clarify the relation of bulk boundary structure to surface contrast. The ring‐match model of Page, Howell, and Ralph as it has been applied to our work is evaluated. Suggestions are made as to the proper use of computer image simulation and it is noted that a better approximation to simulation of grain boundary contrast might be achieved by using computer relaxed grain boundary structures as an input for our image simulation program.

ISSN:0021-8979    

DOI:10.1063/1.1662286

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Isothermal and isochronal annealing measurements were performed on heavily Si‐doped GaAs. Infrared reflectivity measurements were used to determine the free‐carrier concentration after each annealing stage. A factor of [inverted lazy s]5 decrease in free‐carrier concentration was observed as a result of annealing at temperatures as low as 400°C. This annealing effect can be important when fabricating devices using GaAs: Si. Possible explanations of this effect are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662287

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple extension of Miller and Nordland's interference method for determining relative signs of nonlinear optical coefficients is given. The extended method uses a (1/4)&lgr; retardation plate to interchange ``simple'' and ``complex'' interference signals. This makes it possible to determine relative signs of coherence lengths as well as nonlinear coefficients without independent measurements of indices of refraction.

ISSN:0021-8979    

DOI:10.1063/1.1662288

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The thermal conductivity of an Evanohm rod has been measured from 0.4 to 77 K. From these data the thermal conductivity of fine wires of Evanohm may be approximated.

ISSN:0021-8979    

DOI:10.1063/1.1662289

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The threshold intensity of 0.337 mm laser radiation for excitation of the parametric decay instability in a helium arc plasma at 4.0 eV is computed. The plasma density gradient reduces the intensity required from the laser by a factor of 16.

ISSN:0021-8979    

DOI:10.1063/1.1662290

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An error in the previous paper of the same title, concerning the discharge with bulk generated carriers, has been corrected. The conclusions of the previous paper are still qualitatively correct.

ISSN:0021-8979    

DOI:10.1063/1.1662291

出版商:AIP    

年代:1973

数据来源: AIP