摘要:

Changes in the impedance of a coil next to a one‐dimensional layered conductor due to three‐dimensional changes in the conductivity are studied. Eddy current probes are often used to inspect layered one‐dimensional, nonmagnetic metal structures whose electrical conductivity varies primarily with depth beneath the surface. We present a perturbation method, the ‘‘layer approximation,’’ which yields simple and readily evaluated formulas for changes in the impedance of a small coil due to localized three‐dimensional variations in the conductivity. The layer approximation is constructed to be accurate when the conductivity change due to the defect is small or the defect is nearly one‐dimensional. The impedance is calculated and reported for a variety of defects in layered metal structures: voids, inclusions, interfacial roughness, and fasteners. We test the ‘‘robustness’’ of the layer approximation using an extreme case, a flat‐bottom hole in an aluminum plate, as a ‘‘benchmark.’’ Both experimental measurements and more exact theoretical calculations are reported. Impedance measurements were made with a Hewlett–Packard 4194A impedance analyzer for a right‐cylindrical flat‐bottom hole in a 1‐mm‐thick 2024 aluminum alloy plate; the hole was on the side opposite to the coil. Frequencies were varied from 2.5 to 50 kHz. We also calculated the change in the impedance for this benchmark problem using the numerically exact volume integral method. For this benchmark problem, the layer approximation is in good agreement with experiment and more exact theory. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361273

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The behavior of classical time‐domain electromagnetic far fields is investigated with emphasis placed on those characteristics that are unique to the time domain. Necessary conditions are derived for the time‐domain far fields to decay slower than 1/rand for the energy in a far‐field pulse to decay slower than 1/r2. Time‐domain near fields are expressed in terms of integrals over the time‐domain far‐field pattern. Analyticity with respect to angular variation of the time‐domain far‐field pattern is determined, and restrictions are derived on the time dependence of the electromagnetic far fields.

ISSN:0021-8979    

DOI:10.1063/1.361274

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Laser ablation processing for a reaction sintered cubic boron nitride (cBN) by a transversely excited atmospheric CO2laser was found to be strongly affected by the laser wavelength. The ablation threshold of thecBN was 3 J/cm2at 9.3 &mgr;m for the 9R(10) branch but 18 J/cm2at 10.8 &mgr;m for the 10P(38) branch since the 9.3 &mgr;m laser pulse is resonantly absorbed by the transverse optical phonons. Although the reflectance of thecBN surface is very high, it was efficiently ablated by the 9.3 &mgr;m laser irradiation. Hot pressed hexagonal BN samples were also ablated by a 9 &mgr;m band laser as well as a 10 &mgr;m laser, however, a boron rich layer was left on the ablated surface. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361275

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Several near quasicongruent undoped YVO4single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO4single crystals grown by the top‐seeded solution growth technique, were investigated by micro‐probe Raman spectroscopy using unpolarized argon–ion laser light. The line broadening effects of the Raman active mode at 379 cm−1indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO4. In the latter case a value of 9.23 cm−1was measured for full width at half‐maximum. Although the annealing process in O2can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO4crystals, certain remaining peak broadening effects demonstrate a Y–V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm−1frequencies. In addition, nonassigned low intensity extra Raman peaks appeared over 1000 cm−1frequencies in all CZ grown samples. The above detected changes in Y–V–O stoichiometry demonstrate a complex phase system around the homogeneity region of quasicongruent YVO4specimens and enable a more realistic and unified interpretation of the segregated defects and stoichiometry changes in CZ grown YVO4single crystals than previously available. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361276

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An analytical approach to the design of rugate filters with a smooth amplitude modulation of the sine‐wave index is developed. The approach is based on the uniform WKB solutions (asymptotic expansions) of the coupled‐wave equations. A closed‐form solution for the inverse problem (finding the refractive index profile for a given reflectance shape inside the stop band) is found. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361277

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The results of investigations of two‐ and three‐wave mixing in thin holograms are presented. A spatial light modulator fabricated from a Bi12SiO20(or BSO) crystal was used as a photosensitive medium for holographic recording. It was found experimentally that mixing can take place between higher‐order diffracted beams, a phenomenon which uniquely characterizes thin holograms. The necessary theoretical analysis underlying the wave mixing for two specific orientations of the BSO crystal has been developed. We have found qualitative agreement between theory and experiments and concluded that the modulator can be used as an efficient medium for adaptive interferometric techniques. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361278

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The emission properties of a new phosphor based on LiTaO3:Tb3+are described. It is shown to be a storage phosphor, i.e., after previous x‐ray exposure, Tb3+emission in green‐red region of spectrum can be photostimulated by light in 400–800 nm spectral range. Emission centers (Tb3+ions), electron storage centers (oxygen vacancies) and competing nonradiative recombination centers (oxygen ion and Li vacancy couples), are recognized as the key elements in the energy transfer processes and overall emission efficiency of LiTaO3:Tb3+. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361279

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A CO2laser‐based system was used to provoke the vapor‐assisted removal of contaminating particles from different kinds of surfaces. Particles of alumina, silicon carbide, boron carbide, and cerium dioxide, with a size as small as 0.1 &mgr;m, have been efficiently removed from silicon, gold, and silicon dioxide surfaces. The dependence of the cleaning efficiency on the laser fluence was investigated; a threshold was found at 0.65 J/cm2and the efficiency was highest for a fluence ranging from 2.9 to 3.2 J/cm2for silicon, and 3.2 J/cm2for gold and silicon dioxide surfaces. The amount of the water vapor which condenses at the surface was also found to play a major role, the best results being obtained with a condensed thickness calculated to be 6 &mgr;m. The zeta potential value of the contaminant particles with respect to that of the surface greatly influences the cleaning process. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361280

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Multiple energy He+ion implantation to increase the width of the implantation‐induced refraction index barrier in LiB3O5(LBO) is reported. Improvements in planar waveguide transmission (coupling and propagation) at the HeNe laser wavelength of 633 nm, from 5% to 45% for TE polarized light, and from 10% to 28% for TM polarized light in a ∼5‐mm‐long LBO planar waveguide are shown. Annealing is found to increase the transmission (coupling and propagation) at the wavelength of 633 nm of multiple‐energy implanted planar LBO waveguides by as much as 24% for TE polarized light and 71% for TM polarized light. Channel waveguides in LBO fabricated by multiple‐energy ion implantation through a gold wire mask and their use for second‐harmonic generation are reported. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361281

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The problem of doping optical quality polymers with chelated Nd3+has been studied. A number of material systems were evaluated. The best results in terms of optical quality at a high Nd3+concentration were achieved by doping a fluorinated polyimide with fluorinated neodymium chelate. Slab and channel waveguides were fabricated in this material system. Optical absorption and luminescence studies were carried out. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361282

出版商:AIP    

年代:1996

数据来源: AIP