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Showing papers in "Journal of Applied Physics in 1972"


Journal ArticleDOI
TL;DR: In this article, an analysis of laser action in a periodic structure is presented, where the resonant frequencies and threshold criteria for the modes of oscillation have been determined for both index and gain periodicities.
Abstract: An analysis of laser action in a periodic structure is presented. A model of two counter‐running waves coupled by backward Bragg scattering is used. The resonant frequencies and threshold criteria for the modes of oscillation have been determined for both index and gain periodicities. Analytical approximations are given for both the high‐ and low‐gain cases, and computational results for the intermediate regimes.

2,090 citations


Journal ArticleDOI
TL;DR: In this article, a laser velocity interferometer instrumentation system was developed which can measure the velocity history of either spectrally or diffusely reflecting surfaces, and achieved accuracies of 2% or better for peak surface velocities of 0.2 mm/μsec.
Abstract: A laser velocity interferometer instrumentation system has been developed which can measure the velocity history of either spectrally or diffusely reflecting surfaces. The system provides two interferometer fringe signals in quadrature to improve resolution and to distinguish between acceleration and deceleration. Accuracies of 2% or better are attainable for peak surface velocities of 0.2 mm/μsec or more. The system has been applied to the measurement of free surface motion in plate‐impact experiments, and to the measurement of the velocity history of a projectile during its acceleration down a long gun barrel.

1,607 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured hole and electron drift mobilities in thin films of charge transfer complexes of 2,4,7,trinitro-9-fluorenone (TNF) with poly n-vinyl carbazole (PVK).
Abstract: Hole and electron drift mobilities have been measured in thin films of charge‐transfer complexes of 2,4,7‐trinitro‐9‐ fluorenone (TNF) with poly‐n‐vinylcarbazole (PVK). The film compositions ranged from pure PVK to mixtures of TNF : PVK in a 1.1 : 1 molar ratio with respect to the monomer unit. Measurements have also been made on amorphous films of pure TNF. The drift mobilities are extremely low (< 10−6 cm2/V sec) and are strongly field and temperature dependent. The field dependence is due to the measured activation energies decreasing as the square root of the applied field from zero‐field values of about 0.7 eV for both carriers. The field dependence of the mobilities is similar to that observed for conductivity modified by the Poole‐Frenkel mechanism; however, several objections make this model unacceptable for this case. At this time, no satisfactory explanation of the observed field dependence can be given. As the TNF concentration is increased, the hole mobility decreases rapidly, while the electron mobility increases. The results suggest that charge carriers are highly localized with transport taking place by a thermally assisted intermolecular hopping process as for the case of small ppolaron motion. Hole transport is apparently due to hopping via uncomplexed carbazole states, while electron transport is due to hopping between TNF sites which may be complexed or uncomplexed. Estimates of the charge‐carrier localization obtained from the exponential dependence of mobility on the site separation give characteristic distances of 1.1 × 10−8 cm for holes and 1.8 × 10−8 cm for electrons.

866 citations


Journal ArticleDOI
TL;DR: In this article, the collapse of a hollow sphere of incompressible elastic-plastic material, with appropriate pore radius and over-all porosity, has been analyzed.
Abstract: Static and dynamic pore‐collapse relations for ductile porous materials are obtained by analysis of the collapse of a hollow sphere of incompressible elastic‐plastic material, with appropriate pore radius and over‐all porosity. There are three phases of the pore‐collapse process: an initial phase, a transitional elastic‐plastic phase, and a plastic phase. The change in porosity during the first two phases is quite small. In the plastic phase, the static pore‐collapse relation is an exponential law that depends only on the yield strength of the material; the dynamic relation is a nonlinear second‐order ordinary differential equation that involves the yield strength and a material constant (with the physical dimension of time) that depends on the yield strength, the density, the initial porosity, and the pore radius. Comparison of the theoretical predictions with finite‐difference computer‐code calculations for pore collapse of a hollow sphere of compressible material indicates that the effect of elastic co...

556 citations


Journal ArticleDOI
TL;DR: In this paper, a large aggregate of several thousand equal hard spheres was constructed by depositing additional spheres, one at a time, at surface sites on a small seed cluster, placing each new sphere in contact with three already present and not moving it afterward.
Abstract: Aggregates of several thousand equal hard spheres were constructed by depositing additional spheres, one at a time, at surface sites on a small seed cluster, placing each new sphere in contact with three already present and not moving it afterward. Always choosing the site closest to the center of the original seed results in an aggregate showing no evidence of crystallinity, with a pair correlation function quite similar to that of the dense random packings which have been prepared from ball bearings, and to the pair correlation functions calculated from x‐ray diffraction work on amorphous alloys. The packing density ⅙πNσ3/V and the mean coordination number both decrease with distance from the center; the large‐aggregate limits are, respectively, 0.61 (extrapolated, 4% lower than the ball‐bearing value), and exactly 6.0 (in agreement with the ball‐bearing value). The apparent difficulty of homogeneously nucleating crystallization in hard‐sphere systems, even when simultaneous relaxation of many particle positions is allowed, is attributed to the fact that small hcp and fcc fragments are more bulky and have no more hard contacts than amorphous arragements of the same number of atoms.

515 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured wave velocities and elastic moduli at 25°C for hydrostatic pressures to 20 000 psi (excess over 1 atm) for a temperature range of +50°C to −195.8°C.
Abstract: Values of wave velocities and elastic moduli at 25°C were measured for hydrostatic pressures to 20 000 psi (excess over 1 atm). Variations of velocities and moduli at 1 atm were obtained over a temperature range of +50°C to −195.8°C. Adiabatic stiffness moduli (units of 1012 dyn/cm2), their pressure derivatives, and their temperature coefficients (units of 10−5/C), are shown below for 1 atm and 25°C. ModulusValuePressure derivativesTemperature coefficientc1110.79±0.055.98±0.7−1.37±0.2c12 1.24±0.053.06±0.7−5.70±1.5c44 5.78±0.022.98±0.3−1.25±0.1

454 citations


Journal ArticleDOI
TL;DR: In this paper, a computer simulation model is described which applies to the molecular processes involved in crystal growth under very general growth conditions, and the transition probabilities used for adding and subtracting molecules from the crystal and for surface diffusion are shown to satisfy microscopic reversibility in equilibrium.
Abstract: A computer simulation model is described which applies to the molecular processes involved in crystal growth under very general growth conditions. The transition probabilities used for adding and subtracting molecules from the crystal and for surface diffusion are shown to satisfy microscopic reversibility in equilibrium. The computer program uses several internal self‐consistency checks, the results of which support the validity of the simulation method. Growth measurements are obtained in a range above and below the surface roughening temperature. The growth rates of the (100) face of a Kossel crystal show a two‐dimensional nucleation barrier at low supersaturations and below the roughening temperature. An almost linear dependence on supersaturation is observed above this temperature. This result is independent of the amount of surface diffusion. A simple step model is described and the resulting growth rates are compared with the simulated rates of faces containing a fixed number of steps. Agreement is...

438 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the potential of an electrically isolated surface in an rf diode sputtering glow discharge and investigated the influence on these potentials of both the geometry enclosing the discharge volume and of a positively biased auxiliary electrode in contact with the discharge.
Abstract: The plasma potential and the potential of an electrically isolated surface are measured in an rf diode sputtering glow discharge. The influence on these potentials of both the geometry enclosing the discharge volume and of a positively biased auxiliary electrode in contact with the discharge is investigated. It is shown that confining the discharge increases the plasma potential and the energy of positive ions incident on electrically isolated substrates, whereas applying a positive voltage to an auxiliary electrode also increases the plasma potential but does not significantly increase the energy of ions incident on electrically isolated substrates. The effect of rf modulation on the ionic energy distributions is demonstrated. This occurs as the ions pass through the plasma‐substrate sheath and results in a large broadening of the energy distributions of low‐mass species.

406 citations


Journal ArticleDOI
TL;DR: In this article, a one-dimensional acoustical composite-resonator model is used to study the behavior of a quartz-crystal resonator with large mass load, and the exact relationship between the frequency shift and the added mass depends on the acoustic impedance of the deposited material.
Abstract: A one‐dimensional acoustical composite‐resonator model is used to study the behavior of a quartz‐crystal resonator with large mass load. On the basis of this model, it is found that the exact relationship between the frequency shift and the added mass depends on the acoustic impedance of the deposited material. The experimental data for three materials (silver, copper, and lead) with different acoustic impedances are shown to be in good agreement with the theoretical predictions. The validity and limitations of the presently used equations for thickness determination by quartz‐crystal resonators are also discussed.

381 citations


Journal ArticleDOI
TL;DR: In this article, two effects for directly studying thick phase holograms were considered: coupling between the two laser beams used to record a hologram and interference between a readout beam and the diffracted beam within the hologram.
Abstract: This paper considers two effects for directly studying thick‐phase holograms: (a) coupling between the two laser beams used to record a hologram and (b) interference between a readout beam and the diffracted beam within the hologram. Both effects were observed in experiments using single crystals of undoped LiNbO3. The results demonstrate that the holograms arise from electric field patterns caused by either diffusion or drift of photogenerated free electrons.

370 citations


Journal ArticleDOI
TL;DR: In this paper, a property-structure calculation for the influence of supermolecular structures on stiffness properties of a composite material is presented, based on two experimental model systems.
Abstract: Crystalline polymers are hypothesized to behave, with respect to their physical properties, as a multiphase composite solid. Two experimental model systems are employed to illustrate this concept. Illustrative calculations are then presented which employ the micromechanics and macromechanics available in composite theory to develop a property‐structure calculation for the influence of supermolecular structures on stiffness properties. Additional formal comments are then made upon the permissible theoretical techniques in obtaining sensible estimates of the mechanical properties of a heterogeneous material.

Journal ArticleDOI
TL;DR: In this paper, the room temperature electrical properties of ten I•III•VI2 (I=Cu, Ag; III=Al, Ga, In; VI=S, Se) compounds are presented.
Abstract: The room‐temperature electrical properties of ten I‐III‐VI2 (I=Cu, Ag; III=Al, Ga, In; VI=S, Se) compounds are presented. The resistivities of eight of these compounds are rapidly changed by annealing under maximum and minimum chalcogen pressures. The Cu compounds can readily be made p type, a feature lacking in the analogous II‐VI compounds. However, the Cu compounds with energy gaps of 1.7 eV or above have not been made n type.

Journal ArticleDOI
TL;DR: In this paper, a generalized LST relation was used to calculate the permittivity of strontiumtitanate from zero to optic frequencies, and the Curie-Weiss law was satisfied in the temperature range 60-300 °K, giving a Curie temperature of 30 ± 2 °K for the three crystal orientations.
Abstract: The permittivity of single‐crystal single‐domain strontiumtitanate has been measured in detail in the [001], [011], and [111] directions, as a function of temperature (from 4.2 to 300 °K), electric field (from −23 000 to +23 000 V/cm, and frequency (from 1 kHz to 50 MHz). The free energy of the crystal is determined as a function of polarization with temperature as a parameter. The Curie‐Weiss law is satisfied in the temperature range 60–300 °K, giving a Curie temperature of 30 ± 2 °K for the three crystal orientations. The Lyddane‐Sachs‐Teller (LST) relation is satisfied for temperatures between 30 and 300 °K and for electric fields between 0 and 12 000 V/cm. A generalized LST relation is used to calculate the permittivity of strontiumtitanate from zero to optic frequencies. Two active optic modes are important. The lower‐frequency mode is attributed mainly to motion of the strontium ions with respect to the rest of the lattice, while the higher‐frequency active mode is attributed to motion of the titanium ions with respect to the oxygen lattice. The restoring forces that act on the Ti ions begin to "harden" when these ions are displaced approximately 0.002 A from their equilibrium positions.

Journal ArticleDOI
TL;DR: In this article, the temperature dependence of the elastic constants of singlecrystal iron has been measured from 25 to 900°C and a nonlinearity of temperature dependence for the three measured independent constants is associated with the degree of ferromagnetic ordering.
Abstract: The temperature dependence of the elastic constants of single‐crystal iron has been measured from 25 to 900°C. A nonlinearity of temperature dependence for the three measured independent constants is associated with the degree of ferromagnetic ordering. The c′ = (C11−c12)/2 is nonlinear in the paramagnetic region as well. A marked difference in sensitivity to spin order between the c′ and c44 shear constants implies that the exchange interaction is, for the most part, between second, not first nearest neighbors. The nonlinearity in temperature dependence of the elastic constants is used to account for (by means of the Zener theory) the nonlinear Arrhenius plots for the diffusion of carbon and self‐diffusion in α‐iron.

Journal ArticleDOI
TL;DR: In this article, a theoretical model is developed for coupled-film systems consisting of an underlying ferromagnetic thin film and a surface layer of antiferromagnetic material viewed as an assembly of uniaxial small particles.
Abstract: A theoretical model is developed for, and applied to, some coupled‐film systems consisting of an underlying ferromagnetic thin film and a surface layer of antiferromagnetic material viewed as an assembly of uniaxial small particles. The magnetization of the film biases, and is in turn biased by, the particles through an interfacial exchange coupling. Above a blocking temperature, dependent on size, particles are able to reverse rapidly due to thermal fluctuation, thus exhibiting superparamagnetic response. By assuming a physically reasonable distribution of particle sizes, good agreement is obtained between computed curves for temperature and frequency dependence of hysteresis loop displacement and coercivity based on this model and corresponding experimental results for oxidized Permalloy films, reported in a companion paper. This thermal fluctuation model is also applied successfully to the case of oxidized cobalt films as studied by Schlenker. In this case it is necessary to include in the analysis the...

Journal ArticleDOI
TL;DR: In this paper, the reflectivity and other optical constants of metals at high temperatures are discussed on the basis of the Drude theory and the theory of electron-phonon collision.
Abstract: The reflectivity and other optical constants of metals at high temperatures are discussed on the basis of the Drude theory and the theory of electron‐phonon collision. The electron‐phonon collision frequency is dependent on the temperature through the temperature dependence of the phonon population. The temperature dependence of the collision frequency determines that of optical properties of metals. Variations of the real and the imaginary parts of the dielectric constant and of the complex refractive index with temperature are considered. General expressions for the temperature coefficients of the optical constants are given. The reflectivity is shown to decrease with increasing temperature. Numerical calculations were carried out for several metals at a few wavelengths and at temperatures from room temperature to their melting temperatures. The results are given in graphs and in a table. Curves for the reflectivity show that the absolute value of the temperature coefficient of the reflectivity is greater for a metal having a lower reflectivity at room temperature. Calculated values of the reflectivity at room temperature are in reasonable agreement with handbook data. However, the calculated reflectivity for silver at its melting point is not coincident with the reported experimental data (the only data available at present), in spite of the qualitative agreement between our results and the experiment. A brief discussion on possible explanations of the discrepancy is made.

Journal ArticleDOI
TL;DR: In this paper, the importance of lattice-parameter mismatch between the GaAs substrate and the GaxIn1−xP epitaxial layer on crystal growth and properties has been investigated.
Abstract: The importance of lattice‐parameter mismatch between the GaAs substrate and the GaxIn1−xP epitaxial layer on crystal growth and properties has been investigated. Three major effects were observed: (i) The crystal morphology and substrate/epitaxial‐layer interface were found to be nearly perfect for a0 ≈ a0 GaAs and very poor including melt inclusions at the interface for other epitaxial‐layer compositions. (ii) The dislocation density was found to depend on a0 ‐ a0 GaAs varying from 105 to > 108 cm−2. (iii) The excess energy due to lattice‐parameter mismatch was found to perturb the solid composition from the chemical‐equilibrium composition toward the composition which minimizes mismatch; i.e., epitaxial layers with x=0.51±0.01 are grown from Ga–In–P liquids with chemical‐equilibrium solidus compositions ranging from 0.46 to 0.62. The result is that under the growth conditions used, highly perfect epitaxial layers could be grown only near x=0.51 with band gaps near 1.9 eV. Other compositions with EG>1.9 ...

Journal ArticleDOI
TL;DR: In this article, the effects of a change in the chemical environment of an atom in a surface region are manifested in several subtle ways on the measured Auger electron spectra, such as a shift in the energies of the Auger electrons, which is the result of charge transfer and is a measure of the valence state of the atom.
Abstract: The effects of a change in the chemical environment of an atom in a surface region are manifested in several subtle ways on the measured Auger electron spectra. The first, a shift in the energies of the Auger electrons, is the result of charge transfer and is a measure of the valence state of an atom. Examples of this effect are the oxidation results on refractory metals presented here. It is found that measurable changes are found even for submonolayer coverages of oxygen on an otherwise clean surface. The second main effect is a change in the shape of a complex spectrum, which occurs when some of the electrons involved in this Auger process are valence electrons. The best example of this behavior is that of carbon, and it is found that these complex spectra serve as a fingerprint for the identification of the form of the carbon at a surface. Problems and opportunities for the exploitation of both these effects are discussed, the data included here being illustrative of the usefulness of this type of measurement.

Journal ArticleDOI
TL;DR: In this paper, stress waves generated by a giant pulsed laser were used to change the in-depth microstructural and mechanical properties of 7075 aluminum, resulting in an increase in yield strength of 30% over unshocked values.
Abstract: Stress waves generated by a giant pulsed laser were used to change the in‐depth microstructural and mechanical properties of 7075 aluminum. The 0.2% offset yield strengths of 7075‐T73 and unaged 7075 aluminum were increased as much as 30% over unshocked values. Microstructural analyses showed that laser shocking induced a tangled dislocation substructure similar to explosively shocked aluminum.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the elastic surface wave propagation in LiNbO3 and found that the effective electromechanical coupling coefficient of the leaky surface wave propagating along the X axis of a 64° rotated Ycut plane is very large, K2 = 0.113, and the attenuation of this wave, caused by radiation of the energy into the solid, is 0.036 dB/wavelength for a free surface and goes to zero for a metalized surface.
Abstract: Velocities and attenuations of piezoelectric leaky surface waves in LiNbO3 are analyzed. As a result, we have found that the effective electromechanical coupling coefficient of the leaky surface wave propagating along the X axis of a 64° rotated Y‐cut plane is very large, K2 = 0.113, and the attenuation of this wave, caused by radiation of the energy into the solid, is 0.036 dB/wavelength for a free surface and goes to zero for a metalized surface. Moreover, K2 of the elastic surface wave for a 130° rotated Y‐cut, X propagation, is found to be larger than that for a Y cut, Z propagation. The theory is verified experimentally. The theoretical analysis and experiments on amplification are performed for these types of waves. In an experiment utilizing the leaky surface wave, net terminal gain of 13 dB/cm is observed for the interaction between the carrier in 200‐Ω cm Si wafer (0.3×3×10 mm), separately mounted on a LiNbO3 surface, and the leaky surface wave. The air gap between the Si wafer and LiNbO3 single crystal is about 0.5 mμ.

Journal ArticleDOI
TL;DR: In this paper, the tunneling time constant for a three-dimensional δ-function trap is derived and compared with experiments on metal-nitride oxide semiconductor structures, and the results show that the trap can trap in an insulator on top of the metal.
Abstract: Tunneling of charge carriers between a metal (or a semiconductor) and traps in an insulator on top of the metal is studied in this paper. The tunneling time constant for a three‐dimensional δ‐function trap is derived and compared with experiments on metal‐nitride oxide semiconductor structures.

Journal ArticleDOI
Berndt Feuerbacher1, B. Fitton1
TL;DR: In this article, the photoelectron flux under solar irradiation is calculated and methods for controlling photoemission both with respect to the number of emitted electrons and their energy distribution are discussed.
Abstract: Photoemission properties were measured for the materials gold, aluminium, stainless steel, vitreous carbon, Aquadag, graphite, silica, and semiconducting indium oxide. The surfaces were treated so as to simulate the conditions actually encountered in space missions. Results are presented on the reflectance, photoyield, and photoelectron energy distributions up to 25 eV, and on the work function. From the yield curves the photoelectron flux under solar irradiation is calculated. Methods are discussed for controlling photoemission both with respect to the number of emitted electrons and their energy distribution.

Journal ArticleDOI
TL;DR: In this paper, the currentvoltage characteristics of microwave-irradiated superconducting weak links have been calculated on the analog computer and the results of several authors can be interpreted correctly by taking into consideration the resistive feedback.
Abstract: The current‐voltage characteristics of microwave‐irradiated superconducting weak links have been calculated on the analog computer. Experimental results of several authors can be interpreted correctly by taking into consideration the resistive feedback.

Journal ArticleDOI
TL;DR: In this paper, the motion of space charge initially located at the free surface of an insulator is studied as a function of time, and the available experimental data for polyethylene do not fit these simple models, and discrepancies are discussed.
Abstract: The motion of space charge initially located at the free surface of an insulator is studied as a function of time. Analytic results are given for the following cases: (a) mobility proportional to a power of the field; (b) mobility proportional to a power of the free‐carrier concentration; and (c) fast deep trapping which goes to completion. After one transit time, the surface voltage becomes a unique function of time, independent of its initial value. The available experimental data for polyethylene do not fit these simple models, and the discrepancies are discussed. It is also shown that the observation of thermally stimulated currents in thin‐film electrets implies that they are electrically inhomogeneous.

Journal ArticleDOI
TL;DR: In this article, a single-crystal substrate of silicon is covered with evaporated gold and heated at relatively low temperatures (100-300°C) in an oxidizing atmosphere, a silicon dioxide layer is readily formed over the gold layer.
Abstract: When a single‐crystal substrate of silicon is covered with evaporated gold and heated at relatively low temperatures (100–300°C) in an oxidizing atmosphere, a silicon‐dioxide layer is readily formed over the gold layer. The mechanism and factors controlling this low‐temperature oxide formation have been investigated using backscattering of 2‐MeV He+ ions. The oxide layer is nonuniform in thickness and the initial growth of this layer is proportional to (time)1/2. Both oxidizing ambient and orientation of the substrate influence the growth rate, and the amount of gold determines the final thickness of oxide. A model is proposed to explain the oxide‐growth mechanism.

Journal ArticleDOI
TL;DR: The elastic stiffness moduli of a 22-carat Type II diamond have been measured at 25.0°C by the ultrasonic technique described by H. J. McSkimin this paper.
Abstract: The elastic stiffness moduli of a 22‐carat Type II diamond have been measured at 25.0°C by the ultrasonic technique described by H. J. McSkimin. Basic wave velocities were obtained over a frequency range of 20–500 MHz in order to minimize errors due to diffraction and coupling effects. Moduli (in units of 1012 dyn/cm2) are as follows: c11=10.79±0.05, c12=1.24±0.05, c44=5.78±0.02. Comparison with literature values is made.

Journal ArticleDOI
TL;DR: In this paper, it was shown that for specific ratios of sound-to-light wavelengths, there is a substantially expanded angular range over which Bragg interaction can take place, allowing longer interaction lengths between light and sound, which greatly reduces the acoustic power required.
Abstract: Light deflector designs which use the anomalously low shear wave acoustic velocity and high acousto‐optic figure of merit in single‐crystal paratellurite, first proposed by Uchida and Ohmachi, have been made practical by exploiting this material's birefringence to circularly polarized light. Dixon's equations for Bragg interaction in birefringent materials are found to be equally applicable to optically active materials when linearly polarized propagation modes are replaced by circularly polarized modes. For specific ratios of sound‐to‐light wavelengths, there is a substantially expanded angular range over which Bragg interaction can take place. One effect of this increased range is to permit longer interaction lengths between light and sound, which greatly reduces the acoustic power required. In paratellurite, for visible light, this expanded range occurs for sound frequencies below 100 MHz, in the region of acceptable acoustic loss. Examples of possible designs include a deflector only 3×5×7 mm having a capacity of 500 linearly resolvable spots with a random access time of 10 μsec, with 50% of the incident light being deflected at 35‐mW acoustic power.

Journal ArticleDOI
TL;DR: In this article, the theory of infinite chains is used to predict the variation of conductivity with particle concentration, and the factors which determine the critical concentration are discussed, where the authors show that when conducting particles are added to a nonconducting matrix, conductivity increases abruptly at a critical concentration.
Abstract: When conducting particles are added to a nonconducting matrix, conductivity increases abruptly at a critical concentration. The theory of infinite chains is used to predict the variation of conductivity with particle concentration. Factors which determine the critical concentration are discussed.

Journal ArticleDOI
TL;DR: In this article, an analysis of infrared conversion to visible and ultraviolet radiation by Yb3+−Er3+, Yb 3+−Ho3+, and Yb 2+−Tm3+ ions in crystals is presented.
Abstract: An analysis of infrared conversion to visible and ultraviolet radiation by Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in crystals is presented. The expression for the visible power output in the presence of back transfer from the active ion to the energy‐transferring ion (Yb3+) is given and the relationship between the intermediate state transfer and back transfer coefficients for maximum output is found. If this relationship is satisfied the visible output in the presence of back transfer is equal to the maximum output with no back transfer. The behavior of the power output when the transfer and back transfer coefficients depart significantly from this optimum condition is examined and the parameters which govern the power output under these conditions are determined. The analysis is applied to Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in BaYF5 and BaY2F8. Measurements on the brightest composition of Yb3+–Er3+ ions in BaYF5 indicate that the advantage of a long‐lived intermediate state is diminished by back transfer. A power‐conversion efficiency of 0.1% has been obtained for the green emission from BaYF5:Yb3+–Er3+ when pumped by 0.93‐μ radiation from a 17% efficient Si–GaAs diode. Conversion efficiencies of 0.03% are obtained for the green emission from BaY2F8:Yb3+–Ho3+ and for the blue emission at 4800 A from BaYF5:Yb3+–Tm3+. Efficient conversion of 1.5‐μ radiation to the visible by BaYF5:Er3+ is also described.

Journal ArticleDOI
TL;DR: In this paper, the temperature characteristics of dielectric constants, spontaneous polarization, thermal expansion coefficients, indices of refraction, and optical rotatory power of Pb5Ge3O11 single crystals have been investigated in detail from room temperature up to above the Curie temperature, 177°C.
Abstract: The temperature characteristics of dielectric constants, spontaneous polarization, thermal‐expansion coefficients, indices of refraction, and optical rotatory power of Pb5Ge3O11 single crystals have been investigated in detail from room temperature up to above the Curie temperature, 177°C. From the results of these measurements, the following constants were obtained: linear thermal‐expansion coefficients (αa)F=7.75×10−6/deg°C and (αc)F=7.79×10−6/deg°C (ferroelectric phase), (αa)P=13.8×10−6/deg°C and (αc)P=13.4×10−6/deg°C (paraelectric phase); quadratic electro‐optic constants g33T=0.47×108 cm4 /C2, g13T=0.37×108 cm4 /C2; and electrogyration coefficient γ33 =8.7 cm2/C. An isomorphous compound Pb5(Ge2O7)(SiO4) was synthesized and was found to be ferroelectric with T c=60°C and Ps=1.7 μC/cm2 at room temperature. Ferroelectric properties and electrogyration coefficient were studied in the solid‐solution system Pb5(Ge2O7)(GeO4)1−x (SiO4)x.