摘要:

Frame‐camera interferogram data for a neodymium‐doped glass rod taken during the laser pumping process have been analyzed in terms of changes in optical path length due to: (1) explicit temperature‐induced changes in length and index of refraction, and (2) temperature‐induced stress birefringence. Criteria for compatibility of the interferogram data, the formalism, and independently determined values for the phenomenological constants involved are set up and met, after which the temperature over the rod cross section obtains. The minimum in the temperature distribution found accounts for the observed split fringes, and our qualified estimate of the temperature rise at the center of the rod is ∼16°C. Estimates of the changes in optical path length due to the various effects are made, and values for the temperature coefficients of expansion and refractive index of 0.97×10−5/°C±6% and −7.2×10−7/°C±60%, respectively, are submitted.

ISSN:0021-8979    

DOI:10.1063/1.1709995

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In this paper, Fermat's principle is applied to the analysis of pump‐induced optical distortion in isotropic laser materials. This approach leads to expressions for the slope and trajectories of rays through a laser amplifier rod for a plane‐wave input. These results are then used to predict ray refraction, beam divergence, and optical path length through the rod as a function of radius, time, and polarization. The index of refraction of the material is considered to change both as a result of thermal effects and as a result of the presence of an excited ion population.

ISSN:0021-8979    

DOI:10.1063/1.1709996

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper quantitatively describes the optical distortion in neodymium‐doped glass which is induced by pump radiation. We have found the optical path length at 6328 Å dependent on four primary effects: (1) change in physical length; (2) change in refractive index due to temperature rise; (3) change in index resulting from stress; (4) change in index associated with an excited‐state population of neodymium ions. Section I presents the experimental techniques used and the results obtained. Included in this section are measurements of optical‐path‐length variations, pump‐induced birefringence, change in physical length, change in refractive index, bulk temperature rise, and the deflection of a pencil of rays. Section II compares the results of Section I with the theory set forth in the previous paper. Good agreement between theory and experiment is achieved provided a term which takes account of the index change associated with an excited‐state population of neodymium ions is included. This term arises from the fact that the polarizability of the neodymium ion in its excited4F3/2level is different from its value in the4I9/2ground level. The inclusion of this new term in the expression for the change in refractive index implies that large optical distortions can exist in ``athermalized'' glass.

ISSN:0021-8979    

DOI:10.1063/1.1709997

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements of space‐charge‐limited currents have been made on evaporated thin films of the compound copper phthalocyanine using Ohmic contacts. A complete study of the current as a function of voltage, temperature, thickness, and illumination indicates that all the results are consistent with the assumption of an exponential distribution of trapping states of the formNt(E) =kTcP0exp (E/kTc), wherekTcP0is a parameter related to the total trap density.Practical techniques for obtaining values for the mobility, density of states, total trap density, trap distribution in the vicinity of the Fermi level, and trap capture cross section are outlined and values reported.

ISSN:0021-8979    

DOI:10.1063/1.1709998

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements of currents in evaporated thin films of copper phthalocyanine as a function of temperature and ambient have yielded information about the effects of nitrogen, hydrogen, and oxygen ambients on the conductivity, trap density, and mobility. Above a transition voltage the currents are space‐charge‐limited and can be correlated with a trap distribution that decreases exponentially with energy as the distance from the valence band edge increases. The parameters that govern the distribution as well as the position of the Fermi level depend on sample preparation, and some systematic correlation exists between annealing and the subsequent values of these parameters, based on consideration of the crystal changes that occurs on heating.The value of the intrinsic conductivity &sgr;0=3(&OHgr; cm)−1and mobility &mgr;=0.013±0.007 cm2/Vsec have been determined and are found to be relatively independent of preparation and subsequent treatment.

ISSN:0021-8979    

DOI:10.1063/1.1709999

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A steady‐state theory of a discharge column in a magnetic field is presented which covers the intermediate pressure range where the ion mean free path is neither much greater than, nor much less than, the discharge radius. With increasing pressure and magnetic field, its predictions tend to those obtainable from ambipolar diffusion theory. With decreasing pressure they approximate those of low‐pressure discharge theory based on the use of the third‐moment equation for the ions. The analysis in this paper is based on continuity and momentum‐transfer equations for the electrons and ions, but in contrast to linear ambipolar diffusion theory, the nonlinear ion inertia term is retained. In the plasma approximation, retention of this term gives rise to a plasma‐sheath boundary, where the density is nonzero and the potential finite, located where the ambipolar drift velocity reaches the isothermal sound speed [k(Te+Ti)/mi]1/2. Numerical solutions are presented for the profiles of density, velocity, and potential, for planar and cylindrical discharges. These indicate that potential inversion can occur, and that under such conditions the potential rises to a maximum and then decreases towards the plasma‐sheath boundary.

ISSN:0021-8979    

DOI:10.1063/1.1710000

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

It has been found that dislocations in LiNbO3and LiTaO3single crystals can be decorated by electric‐field‐enhanced diffusion of platinum or gold into the crystals at temperatures in the order of 600°C with voltages in the range of 250 to 1000 V/cm. To demonstrate the use of the technique, examples of low‐angle boundary networks in LiNbO3and LiTaO3are shown. The general characteristics of the as‐grown dislocation network in a [101¯0]‐growth‐axis LiNbO3crystal are described, and the effect of annealing on the dislocation array in LiTaO3crystals is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1710001

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A renormalization of the HamiltonianH, previously devised by Silverman and Joseph to calculate the temperature‐dependent ferroelectric‐mode frequency in perovskites exhibiting a second‐order transition, is extended to the case of a first‐order phase change. The extension involves inclusion inHof all anharmonic terms to sixth order which give rise, after a thermal average is taken, to polarization and temperature dependences in the internal energy, which are similar to those appearing in the phenomenological theory of Devonshire. Validity of the latter theory in high electric fields can now be understood as a consequence of field independence of the acoustic modes, which make the dominant contribution to the temperature dependence of the internal energy. Since the optical frequencies must depend on field under these circumstances, so that validity of the Devonshire theory requires that they make little contribution to thermal properties, the optical branch should lie above the acoustic, except in (001) planes where the unstable modes occur which are responsible for the transition. From domain‐wall calculations in the tetragonal phase of barium titanate, it is concluded that dispersion is weak in the (001) planes, so that all frequencies withkin such a plane will be low. This suggests that (001) planes should be surfaces of discontinuity in frequency, which leads in turn to the prediction that the electric susceptibility and switching rate in tetragonal barium titanate will exhibit thickness dependence of purely lattice‐dynamical origin, with the thickness dependence of the latter exceeding that of the former. The theory thus provides a means of correlating the field and thickness dependence of switching and polarization with the structure and temperature dependence of the lowest transverse optic branch.

ISSN:0021-8979    

DOI:10.1063/1.1710002

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A lattice‐dynamical approach to calculation of the switching probability is developed for use in connection with the Miller‐Weinreich model of 180° domain‐wall motion in barium titanate single crystals. According to the new approach, the nuclei of permanently reversed polarization, which appear on the domain‐wall surface in the presence of a field, are produced by a superposition of optic modes. The probability that this superposition will attain the amplitude required to switch a nucleus can be calculated as the probability for the outcome of a random walk. This probability is a function of the optical frequency and of the number of modes which contribute to switching. From a previous renormalization of the Hamiltonian which describes the lowest transverse optic mode, the field and thickness dependence of the parameters which govern switching can be determined. In this way it is predicted that (1) the product of field and activation energy will increase with the field; and (2) the thickness dependence of the switching activation energy, which is primarily of lattice‐dynamical origin, should exceed the corresponding thickness dependence of the electric susceptibility measured on the same crystal. The role of the surface layer is assumed, following Janovec, to lie in the production of backswitched microdomains behind the advancing domain wall. This backswitching can produce electrostatic fields which retard the wall in the same way as depolarization fields which earlier theories have attributed to charges deposited on the inner surface of an unswitched layer. This picture of retardation permits us to separate the mechanism which slows the wall from that which accounts for the thickness dependence of switching and thus to avoid contradictions which have arisen in attempts to explain the latter effect by depolarization fields.

ISSN:0021-8979    

DOI:10.1063/1.1710003

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An analysis of the time dependence of avalanche processes encountered in silicon junctions, including the effects of different ionization rates and velocities of the two charge carriers, is presented. An earlier analysis of Read was restricted to equal ionization rates and velocities; that restriction has been removed but the frequency limitation of his analysis has been retained here. Various solutions of the generalized differential equation are obtained, including a steady‐state solution to a sinusoidal perturbation of the avalanche‐field maximum. The important features of this steady‐state solution are that it describes the avalanche current for all explicit values of the multiplicationM≥1, is valid for highly nonlinear responses to the sinusoidal perturbation, and contains both the in‐phase and out‐of‐phase parts of the fundamental‐frequency component of the avalanche response.The analysis is applied to solid‐state photomultipliers, is used to explain an anomalous rectification observed in operating Read structures, and, lastly, the small‐signal limit of the avalanche response is compared with susceptance measurements of a uniformly avalanching junction as a function of the multiplication and saturation current over a frequency range of 20 to 200 MHz.

ISSN:0021-8979    

DOI:10.1063/1.1710004

出版商:AIP    

年代:1967

数据来源: AIP