Van E. Wood

Decoupling approximation for the nonlinear-optical response of composite media

A nonlinear decoupling approximation (NDA) is described for calculating the nonlinear-optical response of composite materials. The NDA is used in conjunction with the effective-medium approximation for the linear response to calculate the effective third-order susceptibility, χe, of model metal–insulator and semiconductor–insulator composites as a function of frequency and composition. It is found that the ratio χe can be strongly enhanced relative to χ1, the corresponding third-order nonlinear susceptibility of a pure constituent in bulk. The enhancement is found to be sensitive to composite topology as well as to composition. The nonlinear susceptibility of randomly oriented nonlinear ellipsoidal particles in a linear host is calculated in the dilute limit. The susceptibilities of the model composites are also shown to be strongly influenced by particle shape.

Guided-wave optical properties of sol-gel ferroelectric films

Sol‐gel processing methods have been used to prepare thin films of lead titanate, Pb(Zr,Ti)O3, and Pb(Mg1/3Nb2/3)O3 on sapphire and single‐crystal strontium titanate substrates. These films have been characterized using x‐ray diffraction, optical waveguiding measurements at 633 nm wavelength, and optical transmission measurements. The films, in general, contain a mixture of perovskite and pyrochlore phases, with perovskite formation being favored by higher processing temperatures, by use of the SrTiO3 substrates, and by the addition of excess lead precursor compound to the starting solutions. The films have refractive indices close to, but lower than, those of the corresponding bulk materials. The reduction of the refractive indices from the bulk values is believed to result primarily from incomplete densification. Transmission measurements show that the optical dispersion in the PbTiO3 films is similar to that in the bulk crystal. Although all films showed scattering losses, waveguiding over distances up...

Focal properties of geodesic waveguide lenses

The focal properties of uncorrected geodesic lenses in ion‐exchanged glass waveguides are reported. A 13.8‐mm‐focal‐length lens resolved by beams with an angular separation of 27.6 mrad, while a 28‐mm‐focal‐length lens resolved beams with an angular separation of only 3.3 mrad. Intensity profiles of the focal region of the former lens revealed a 40‐μ spot size when the input aperture was 5 mm, and a spot size of 7.7 μ when the aperture was reduced to 1 mm. This value is close to the diffraction‐limited spot size of 5.7 μ.

Magnetic properties of heavy-rare-earth orthomanganites

Abstract The orthorhombic phases of YMnO3, HoMnO3 and YbMnO3 were made by transformation of the normal hexagonal phases at 1000°C and 35–40 kbar. The magnetic susceptibilities were measured from 4·2 to 400 K. Antiferromagnetic ordering is evident at 42 K for YMnO3 and 9 K for HoMnO3. The paramagnetic Curie temperatures were decreased considerably in magnitude from those of the hexagonal phases, being −67 K for YMnO3, −23K for HoMnO3 and −83 K for YbMnO3. HoMnO3 is metamagnetic below 9 K. In YbMnO3 and HoMnO3, both the rare-earth and Mn ions carry approximately their full moment. The magnetic structures are discussed in comparison with the orthoferrites. It is shown that strong Jahn-Teller distortion around the Mn3+ ion leads to a slight reduction in the lattice parameter c(b′), and thence to the low magnetic ordering temperatures.

Holographic formation of gratings in optical waveguiding layers

Thick phase gratings were formed photorefractively (through optically induced refractive index changes) in planar optical waveguides by intersecting short−wavelength coherent guided beams. In multimode guides formed by effusing Li from LiNbO3, maximum diffraction efficiencies were 52% at the 0.488−μm write wavelength and 3.1% at 0.633 μm. In a two−mode LiTa1−xNbxO3 guide formed by diffusing Nb into LiTaO3 at 1100 °C, diffraction efficiencies were 65% and 28% at the same two wavelengths, respectively.

Soluble saturable refractive-index nonlinearity model

Abstract TE modes of an optically linear planar waveguide on a thick nonlinear substrate are described for a model substrate refractive index or dielectric permittivity of the form ϵ= ϵ s + ϵ sat u(2+u) (1+u) 2 , where u= α|E| 2 2ϵ sat , which displays saturation at high guided-wave powers, yet for which wave equation integration and power integrals are elementary. The parameter γ= ϵ sat (ϵ f –ϵ s ) where ϵf is the guiding-layer permittivity, determines the guided-wave behavior. For γ 1, power limiting and interface guiding are observed, similar to the Kerr model except for the saturation effect.

Large-angle optical switching in waveguides in LiNbO3

Abstract Optical waveguiding layers displaying great photorefractive sensitivity have been formed by diffusion of iron into LiNbO3. Thick phase gratings of greater than 50% diffraction efficiency have been formed within such waveguiding layers by intersecting guided beams of red light from a He-Ne laser. By writing the gratings in a sample heated to 160°C, fixed gratings of about 1% diffraction efficiency have been produced. Modulation of the diffracted beam by electro-optic deflection of the input beam has been demonstrated.

Theoretical Solutions of Grain‐Boundary Diffusion Problem. Approximations and Interpretation of Experiments

Whipples exact solution to the idealized grain‐boundary diffusion problem has been evaluated numerically for ranges of parameters appropriate to existing and contemplated experiments. From these evaluations the concentration at the grain boundary, the integrated concentration at fixed depth of penetration, and the angle at which isoconcentration contours intersect the grain boundary are obtained, these results being presented in either tabular or graphical form. The ranges of validity of approximate solutions obtained by various authors are discussed on the basis of the numerical results, as is the use of the graphs and tables for the interpretation of experimental data.

Stoichiometry dependence of lithium outdiffusion in LiNbO3

Measurements by Mach‐Zehnder interferometry of the refractive‐index changes near the surface of outdiffused LiNbO3 crystals indicate that, in agreement with recent results of Noda et al. [J. Appl. Phys. 51, 1379 (1980)], the rate of lithium outdiffusion is greater for more nearly stoichiometric crystals. The activation energy for diffusion of Li does not vary significantly with stoichiometry. The Li diffusion coefficient is also higher in the relatively Li‐depleted regions near the surface.

Surface and Grain‐Boundary Diffusion of Gold‐Copper

The diffusion of gold into copper grain boundaries from thin sources has been studied from 760° to 625°C. The activation energy for the grain‐boundary diffusion of gold into copper is 25 kcal/mole. At the lower temperature, there was observed surface depletion of gold at the grain boundary in accordance with theoretical solutions. The surface diffusion of gold on copper (100) surface was studied from 705° to 580°C under 10−9 Torr. The activation energy for surface diffusion was about 25 kcal/mole. The rates of surface diffusion were found to be less than those for grain‐boundary diffusion at the same temperature. Gold‐copper whiskers were generated adjacent to the grain boundaries for diffusion at or below 660°C. The growth of such whiskers is diffusion‐controlled and is attributed to the stress resulting from volume increase due to gold diffusion into the grain boundary.