摘要:

The inverse problem of defect characterization is carried out by comparing theoretical and experimental return echo pulses. Acoustic echo signals of the order of 2 ns long are digitized and fed into a digital computer. A Wiener filter is designed to match the transducer response, so the impulse response of the system approaches a &dgr; function. Experimental results on defects in Si3N4ceramics are presented which demonstrate the power of such a technique for defect characterization.

ISSN:0003-6951    

DOI:10.1063/1.90529

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We report on a new surface‐acoustic‐wave (SAW) amplifier and generator on a monolithic MIS structure with a uniform pump electrode. The gain for the forward SAW and the generation of the backward SAW have been observed in an Al/ZnO/SiO2/Si structure. Using the same structure, we observed for the first time the parametric generation of SAW of 222 MHz by the uniform pumping, even if there is no signal input.

ISSN:0003-6951    

DOI:10.1063/1.90530

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

LEED and AES studies of LaNi5single crystals cleaved in UHV and exposed to oxygen and hydrogen show that surface segregation of La is induced at room temperature by oxygen, but not by hydrogen. This segregation is driven by the chemical exchange reaction (La‐Ni)+O→ (La‐O)+Ni. A surface‐layer model is derived supporting the important implications of the segregation for the excellent kinetics in hydrogenation and the resistance to contaminants.

ISSN:0003-6951    

DOI:10.1063/1.90531

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The density of the compressed neon core in laser‐imploded neon‐filled microballoons was measured by the shift to longer wavelengths of the free‐bound x‐ray continuum edges due to the recombination processese−+Ne+9ande−+Ne+10. The results are shown to be in good agreement with those obtained by fitting Stark profiles to neon x‐ray lines. Density measurements based on continua will be particularly important at higher densities where most spectral lines of the neon ion would disappear due to pressure ionization.

ISSN:0003-6951    

DOI:10.1063/1.90506

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Electron‐beam‐focusing experiments using tapered hollow cathodes have been performed at power levels exceeding 1012W and with diode aspect ratios (radius/anode‐cathode spacing) of 24 and 45 (uncorrected for plasma motion). The spatial distributions of both the electron (using collimatedp‐i‐ndiodes) and ion currents (using quartz pressure gauges and Faraday cups) were measured simultaneously. Efficient electron‐beam pinches were produced at largeR/d(≈24) using a diode configuration that employed a small‐diameter cathode and heated anode.

ISSN:0003-6951    

DOI:10.1063/1.90532

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Extension of previous work on beamlet‐beamlet interaction is made in two phases. The effect of beam space‐charge truncation due to electrode shielding is considered. For a typical geometry multiaperture source, the ion divergence is thus reduced by a factor of 30, assuming all the beamlets interact with each other, and by a factor of 5, assuming only nearest‐neighbor beamlets interact. To account accurately for electrode shielding, a direct solution to the Poisson‐Vlasov equation was made for a similar physical situation. For a typical circumstance it shows an additional decrease of a factor of 5 for both the global and nearest‐neighbor calculation. These results indicate that beamlet‐beamlet interaction is small for typical ion sources.

ISSN:0003-6951    

DOI:10.1063/1.90533

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Single‐mode fibers which maintain linear polarization are described. The fibers are birefringent and linear polarization is maintained along either of the two principal axes. The birefringence arises from the deliberate enhancement of anisotropic strains.

ISSN:0003-6951    

DOI:10.1063/1.90534

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Angular scanning of the far‐field intensity peak of a GaAs/GaAlAs DH injection laser is demonstrated. This scan is accomplished by adjusting the current levels between two closely space stripe contacts, thereby creating an asymmetric gain/refractive index profile through which the laser beam propagates. Thus, this effect is somewhat analogous to passing the laser beam through a wedge. A deflection of the peak laser beam intensity of ±14° along thep‐njunction plane is observed.

ISSN:0003-6951    

DOI:10.1063/1.90507

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A new class of saturable absorbers for 10‐&mgr;m applications using doped alkali halides is demonstrated. For the ReO−4molecular ion in KCl, the vibrational transition saturates like an ideal two‐level system. This behavior is a result of the large anharmonic shift in the absorption spectra of the dopant ion. Saturation parameters of 1.45 MW/cm2and a relaxation timeT1of 120 ps are measured at room temperature.

ISSN:0003-6951    

DOI:10.1063/1.90508

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The radiative lifetimes of the HgBr(B) and HgI(B) states have been determined to be 23.7±1.5 and 27.3±2.0 ns, respectively, by fast photolysis of HgBr2and HgI2using e‐beam‐excited ArF and KrCl fluorescence. This experimental approach generated simple exponential decay curves which facilitated measurement of the lifetimes and the rate of quenching of the excited HgX(B) states by HgX2(X=Br or I) molecules. Although the lifetimes reported here are in agreement with previous experimental measurements, they contradict a recently published theoretical calculation.

ISSN:0003-6951    

DOI:10.1063/1.90509

出版商:AIP    

年代:1978

数据来源: AIP