摘要:

The threshold microwave‐field amplitudehcritrequired for the unstable growth of spin waves has been investigated for oblique pumping with a linearly polarized microwave field applied at an arbitrary angle with respect to the static magnetic field. The experiment was performed on YIG (1% Dy) spheres at 9.2 GHz, using a rectangular TE102cavity and a pulsed magnetron source. Data were obtained at static external fields of 400, 600, 1100, and 1500 Oe. In general,hcritincreases with the pump angle. Theoretical expressions for the oblique pumpinghcrithave been derived for ferromagnetic insulators of ellipsoidal shape and with axial symmetry about the direction of the static magnetic field sufficient to saturate the sample. The threshold field is determined by maximizing 1/h=cos&psgr;/h∥±sin&psgr;/h⊥with respect to the angle between the internal field and the spin‐wave propagation direction. Here,h∥andh⊥are the parallel and perpendicular pump threshold fields of Schlo¨mann and Suhl. For external fields sufficient to magnetize the spherical samples to saturation, the theoretical predictions are in good agreement with the experimental data. For small fields, the agreement is poor. However, fair agreement is obtained by assuming a transverse demagnetizing factorNtgreater than the value of ⅓, which is appropriate for saturated spherical samples. The value ofNtfor the best theoretical fit depends on the way in which the sample is demagnetized. This result indicates that for samples not magnetized to saturation, the magnetic structure consists of elongated domains, and that the oblique‐pumping data can be explained from the theory for saturated systems, assuming demagnetizing factors appropriate to the domain structure.

ISSN:0021-8979    

DOI:10.1063/1.1657026

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The S.B.S. steady‐state gain is derived taking into account the energy‐transfer relaxation properties of the liquids. Calculation of the gain for C6H6and CCl4are performed. Quantitative comparison between experimental and theoretical gain inn‐hexane, ethyl‐ether, and CS2are also derived.

ISSN:0021-8979    

DOI:10.1063/1.1657027

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Some observations on the microstructure of Czochralski‐grown fluorapatite, Ca5F(PO4)3, single crystals are presented. From etching and x‐ray topographic studies we have found that slip in this material is on (101¯0) planes, with one Burgers vector in thecdirection, and another in the basal plane and probably along the [101¯0] direction.

ISSN:0021-8979    

DOI:10.1063/1.1657028

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The speed of response of extrinsic germanium photoconductors is limited by the dielectric relaxation response time &tgr;&rgr;=&egr;&egr;0&rgr;, when the resistivity of the photoconductor rises to the M&OHgr;·cm or higher resistivity range. Further, dielectric relaxation components appear only when the drift length of charge carriers is comparable to or greater than the interelectrode distance. The appearance of the dielectric relaxation response‐time component arises when a significant fraction of the photogenerated charge carriers is swept out of the photoconductor before recombination leaving a space charge throughout the crystal. For mercury‐and copper‐doped germanium photoconductors which were studied, an enhanced photosensitivity is observed with increasing bias. For low backgrounds, or high‐resistivity conditions, the effect is largest and appears to correlate with the onset of the dielectric relaxation effects.

ISSN:0021-8979    

DOI:10.1063/1.1657029

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A sintering model is proposed by which all of the significant mechanisms of material transport may be identified, even though more than one mechanism may be operating simultaneously. For diffusion‐controlled sintering it is possible to calculate both the volume and the grain‐boundary diffusion coefficients from measurements of neck size, shrinkage, and shrinkage rate. Furthermore, the surface diffusion coefficient may be estimated through computer synthesis of the sintering curves. Preliminary results on iron and copper have yielded values of the diffusion coefficients which are in good agreement with those measured by other techniques.

ISSN:0021-8979    

DOI:10.1063/1.1657030

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A three‐wavelength laser heterodyne system for plasma diagnostics has been developed using the 0.6328, 1.15, and 3.39 &mgr; transitions in He&sngbnd;Ne. In order to use the 3.39 &mgr; transition, an experimental technique has been developed to measure the dispersion introduced by the lasering atoms under the same conditions that are used for plasma measurements. The dispersion‐corrected 3.39 &mgr; data, when combined with the data at 1.15 and 0.6328 &mgr;, give excellent agreement in the measurement of temporally and spatially resolved electron densities and changes in neutral densities in the afterglow of a pulsed argon discharge. The electron‐density measurements agree with integrated electron‐density measurements made with a microwave cavity operating in the TM010mode.

ISSN:0021-8979    

DOI:10.1063/1.1657031

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Measurement of internal friction at strain amplitudes <10−5in In‐rich In&sngbnd;Tl alloys has shown an amplitude‐dependent peak associated with the fcc→fct martensitic transformation. The peak is thermally activated when the transformation occurs near the melting pointTm, but not at lower temperatures. It is suggested that the peaks originate from the stress‐assisted motion of twin boundaries that are known to spontaneously coalesce immediately below the transformation temperature. The activation energy associated with the transformation peak nearTmis 10–13 kcal/mole higher than for the diffusion of Tl in In. A mechanism is proposed for this relaxation, invoking an interaction between twin boundaries and solute, whereby reordering of solute is effected in differently orientated tetragonal regions by twin‐boundary motion. Shear modulus measurements indicated abrupt changes at the transformation temperature and positive temperature coefficients of modulus in the high‐temperature fcc phase, implying structural instability and an ``entropy‐elastic'' state. At 0.9Tm, about 60% of the elasticity in a 19.5% Tl&sngbnd;In alloy arises from a change in vibrational entropy with extension. The results are consistent with the known crystallography of the transformation.

ISSN:0021-8979    

DOI:10.1063/1.1657032

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Optical absorption‐edge shifts of up to 1.5 eV have been observed for GaP films deposited in textured polycrystalline states and in the amorphous state. The amorphous‐crystalline transition occurs for a substrate temperatureTsof about 240°C. The films deposited at 240°C≤Ts≤270°C exhibiting the large optical absorption‐edge shift are nontransparent, metallic‐appearing, and exhibit a strong [110] texture. The amorphous films deposited at just below 240°C exhibit the same optical properties. With increasingTs, the films exhibit decreasing optical absorption‐edge shifts, becoming transparent‐yellow forTs≥425°C. However, a bulk optical behavior is achieved only by annealing the films at temperatures up to 600°C. The principal textures found by x‐ray diffraction are [110] for 240°≤Ts≤270°C, and [111] forTs>350°C. Reflection‐electron‐diffraction (RED) observations agree substantially with those obtained by x ray, but also indicate some mixed textures. A weak (101¯0) reflection is observed by both x rays and RED, indicating an incipient hcp phase; it is shown that this is not causally related to the optical‐edge shift. X‐ray lattice‐constant measurements over the range ofTsfrom 250°–425°C indicate no observable systematic deviation from bulk values; these observations rule out any causal relationship between changes in lattice constant and the optical absorption‐edge shift. Extinction bands or bounded‐plasma resonance effects do not seem to be able to explain the experimental behavior; the shifts are most probably due to large concentrations of self‐compensated natural defects. It is emphasized that these as‐deposited and annealed GaP films cover the entire absorption spectrum (&agr; vsE) of all III‐V compounds (except InAs and InSb) plus Ge and Si.

ISSN:0021-8979    

DOI:10.1063/1.1657033

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Efficient second‐harmonic generation (SHG) at 5300 Å has been achieved with KDP and LiNbO3crystals when Nd‐glass lasers of high radiance and narrow bandwidth were used. With KDP and a diffraction‐limited laser system having a 19 Å bandwidth, 15 J of radiant energy at 5300 Å were obtained with a 51% energy‐conversion efficiency. Since the harmonic light pulse was narrower than the fundamental pulse, the peak‐power‐conversion efficiency was 70%. The peak power in the green was 1.0 GW. The ratio of harmonic‐fundamental pulse duration increased as SHG increased into the saturation region as expected. For LiNbO3, the relatively large dependence of phase‐matching angle on wavelength limits the maximum SHG efficiency to several percent when broad‐band lasers are used. With LiNbO3, therefore, a laser system was used having mode selectors which limited the bandwidth to less than 0.5 Å while the beam divergence was 1.5 mrad. In this case 21% energy conversion and 33% peak‐power conversion were obtained with a fundamental flux density of only 2 MW/cm2inside the crystal. The values found for the elements of the nonlinear dielectric tensor, corrected for the random multimode nature of the laser, ared36(KDP) = (1.1±0.1)×10−9esu andd31(LiNbO3) = (17±6)×10−9esu. At low conversions a laser beam with fluctuations due to random multimoding is expected to give as much as twice the harmonic produced by a single‐mode laser. At high conversions in the saturation region this ``doubling'' does not occur as verified by our measurements.

ISSN:0021-8979    

DOI:10.1063/1.1657034

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Magnetic susceptibility measurements are reported in the range of the hcp &egr; and &eegr; phases of the Ag&sngbnd;Zn system. The observed trend suggests that a minimum occurs in the magnetic susceptibility of the conduction electrons within the phase field of the &egr; phase at an electron concentration of approximately 1.8 electrons per atom. In the &eegr; phase the magnetic susceptibility increases rapidly, but the trend is less steep than that extrapolated from the &egr; phase. The results show certain similar features with the measurements of the lattice spacings and of thermodynamic properties reported in the literature. The magnetic susceptibility of the &egr; phase alloys can be related to the possible interactions between the Fermi surface and the Brillouin zone, but the behavior of the susceptibility in the &eegr; phase appears to be also dependent on local interactions between zinc atoms.

ISSN:0021-8979    

DOI:10.1063/1.1657036

出版商:AIP    

年代:1969

数据来源: AIP