摘要:

The velocity of energy circulation associated with the uniform precession mode in a ferrite sphere is studied. Specifically, the effect of the boundary conditions imposed by a concentric conducting spherical cavity is considered for the uniform precession magnetic resonance mode of a yttrium‐iron‐garnet (YIG) sphere. Theoretical analyses show that there is a critical ratio between the radius of the ferrite sphere and the conducting cavity where the energy velocity of the uniform precesion mode approaches zero. Spin wave instabilities, as a result of the nonlinear coupling of the uniform precession mode to spin wave excitations, are brought on if the rf‐energy density inside the ferrite exceeds a specific threshold value. Thus a decrease in the energy velocity is expected to decrease the amount of incident power required for the onset of spin wave instabilities. We report that decreases in threshold power for the Suhl first order spin wave instability have been observed as a function of the cavity radius. The experimental cavity consists of two conducting partial hemispheres, one on each side of the YIG sphere.

ISSN:0021-8979    

DOI:10.1063/1.332451

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Measurements of the complex permittivity at 107.3 GHz ofn‐type silicon specimens in the 5–50 &OHgr; cm resistivity range were made using a free space reflection/transmission technique. Reflectance measurements on specimens in the 0.004–5 &OHgr; cm range were obtained. All measurements were compared with a single relaxation time Drude model and a more complete model that was developed which includes Fermi–Dirac statistics and energy dependent lattice and impurity scattering. Although the Drude model was found to reliably predict the complex permittivity ofn‐type silicon over a specified range of resistivity, it has limitations which are discussed.

ISSN:0021-8979    

DOI:10.1063/1.332452

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A detailed study of the polarization and depolarization behavior of 7:65:35 and 8:65:35 lead lathanum zirconate titanate transparent ceramics under dc bias and constant heating rates has been carried out. The dielectric permittivity exhibits a new anomaly near 0 °C in freshly thermally depoled samples which is associated with a buildup of macrodomains and the development of a remanent polarization. From continuity of the dispersive behaviors it is suggested that the dielectric change at the so‐called &agr;–&bgr; transitionTdis not a conventional phase change, but rather is a loss of macro‐ordering and a decay back to a disordered microdomain texture.

ISSN:0021-8979    

DOI:10.1063/1.332453

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Information about the optical absorption coefficient of solid materials in contact with a fluid phase can be obtained from photothermal deflection (PDS) measurements using both the signal amplitude and phase channels of the PDS response of a system to an optical excitation. This paper presents a theoretical model of photothermal processes in the transverse (TPDS) experimental configuration. The theory is used to determine the dependence of both signal channels on the optical absorption coefficient of the solid material and to define absorption coefficient ranges within which TPDS can be used as a spectroscopic technique. A method concerning the use of the combined amplitude and phase data for the absolute measurement of the absorption coefficient is presented for the experimentally important thermally thick limit.

ISSN:0021-8979    

DOI:10.1063/1.332454

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A theoretical model for photoacoustic spectroscopy with light scattering samples is discussed. Some special cases are derived and the nature of the measured signal and the underlying physics are analyzed. Comparisons with transmission and diffuse reflectance spectroscopy are made.

ISSN:0021-8979    

DOI:10.1063/1.332455

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Optical spectra and emission lifetimes are measured for three Nd:Y3Al5O12crystals grown by the floating zone method. The properties are almost the same as those of crystals grown by the conventional Czochralski method. The induced emission cross sections obtained for the three samples are 7.4, 5.3, and 7.0×10−19cm2. These values are comparable to those reported so far.

ISSN:0021-8979    

DOI:10.1063/1.332456

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Undoped, Ge‐, and Sn‐doped GaAs1−xSbxgrown by liquid phase epitaxy have been investigated by means of photoluminescence. Four main peaks have been observed at 11 °K in the undoped samples. One of themK1at 1.513 eV in GaAs and the two,K2andK3, at 25 and 62 meV, respectively, below the band gap energy show an evolution withxparallel to the band gap variation. The remaining one at 1.31 eV does not change appreciably with the Sb content.

ISSN:0021-8979    

DOI:10.1063/1.332457

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A set of luminescence lines previously observed only in GaAs layers grown by molecular beam epitaxy (MBE) has been observed for the first time in layers grown by metalorganic vapor phase epitaxy (MOVPE). The lines which appear between 1.5515 and 1.504 eV are more evident in samples grown with low arsine concentrations and low substrate temperatures. It appears that these additional lines are due to recombinations involving native defects. Unlike the MBE case, extrinsic impurities from the reactants are incorporated in the layers during the growth, thus reducing the concentration of native defects responsible for the additional lines.

ISSN:0021-8979    

DOI:10.1063/1.332458

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The thermoluminescent (TL) properties of many LiF samples have demonstrated a strong influence on trace impurities and impurity content on the TL process. Hence, the general validity of any particular model must be tested against its applicability in a standard material such as Harshaw LiF (TLD‐100). In this paper the validity of the use of Harshaw LiF(54) by Mayhughetal. in their model development for the TL process in LiF is demonstrated by comparing the TL and optical properties of LiF(54) with TLD‐100. The specific properties of optical absorption bands at 310 and 380 nm, theFband near 250 nm, and theZ3band near 225 nm are intercompared with observed TL peaks in both materials. Both the gamma and uv‐exposure behavior of theZ3center demonstrates a direct relationship betweenZ3and TL peak 10, while no direct conversion betweenZ3and the 310‐nm band is observed in TLD‐100. These results do not support recent models identifyingZ3with TL peak 6 andZ2with the 310‐nm band (and TL peak 5); this is probably due to differences in purity and defect state in the LiF samples used by other investigators, emphasizing the need for standardization of materials in this system.

ISSN:0021-8979    

DOI:10.1063/1.332459

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Thin planar aluminum targets were irradiated with 8‐nsec‐duration low‐intensity (∼3×1013W/cm2) glass laser pulses in order to analyze the plasma expansion from both the front and back‐target surfaces. An array of vacuum‐ion calorimeters and Faraday cup charge collectors was used to determine the conversion from incident laser energy to plasma kinetic energy and to determine the ion mass balance of the laser‐produced plasma. Our experimental results do not agree with the ablation structure predicted by simple models or 1‐D numerical simulations. The experimental results and 2‐D calculations indicate that a jet of plasma forms on the back target surface and ablative acceleration of these thin‐foil targets does not occur.

ISSN:0021-8979    

DOI:10.1063/1.332460

出版商:AIP    

年代:1983

数据来源: AIP