摘要:

We have investigated the preionization characteristics of x ray for a transversely excited, multiatmospheric pressure CO2laser amplifier with an active volume as large as 225 cm3. The x‐ray dose required for uniform avalanche discharge is measured as a function of pressure up to 10 atm. The dependence of the input energy density of the main discharge on the x‐ray dose is also investigated.

ISSN:0003-6951    

DOI:10.1063/1.96991

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report experimental demonstrations of the use of a photorefractive barium titanate ring passive phase conjugate mirror in the coherent coupling of two GaAlAs diode lasers. By cooling the crystal towards its tetragonal to orthorhombic phase transition, we were also able to achieve infrared photorefractive phase conjugation with gain.

ISSN:0003-6951    

DOI:10.1063/1.97009

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The characteristics of novel reverse‐biased waveguide phase modulators are reported. These devices, which use the translation of a depletion edge, have provided the highest efficiency figure of merit (56 °/Vmm) ever reported for a reverse‐biased device. Furthermore, the speed of the device is only limited by theRCtime constant. The investigated devices were GaAs/AlGaAs ridge waveguide modulators, a geometry which is well suited for integrated optoelectronics.

ISSN:0003-6951    

DOI:10.1063/1.96992

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Photoluminescence linewidths and transition energies have been measured in GaAs‐AlGaAs multiple quantum wells with large (≥160 A˚) barrier widths as a function of applied transverse electric field. The experimental data agree well with values calculated by using a recently developed variational technique. It is apparent that heterointerface roughness is the dominant line broadening mechanism. The emission intensity decreases rapidly with field, principally due to carrier tunneling at high fields. At 80 kV/cm a shift of 20 meV in the emission energy is observed.

ISSN:0003-6951    

DOI:10.1063/1.96993

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In a system of alternating parallel elastic solid layers (plates) and viscous fluid layers (channels), two types of waves propagate parallel to the layers in the low‐frequency limit. They are related to fast and slow waves in Biot’s theory of wave propagation in porous media. The slownessess0 fastands0 slowobtained previously for the case of inviscid fluid layers between elastic plates are modified to reflect dispersion and attenuation due to fluid viscosity. Two important dimensionless dynamic parameters areL=&fgr;H/&dgr;, whereHis the period width, &fgr; is the relative width of the fluid channel, i.e., the ‘‘porosity,’’ and &dgr;=(2&ngr;/&ohgr;)1/2is the viscous skin depth, and &OHgr;=&ohgr;&fgr;H/&agr; fwhich is channel width times the fluid wave number. Here &ngr; is the kinematic viscosity of the fluid, &agr; fis the fluid sound velocity, and &ohgr; is the radial frequency. In the frequency range for whichLis very largeL≫1 and &OHgr; is very small &OHgr;≪1, the attenuation and dispersion of both slow and fast waves exhibit similar dependences onL.In particular, both wave velocities are decreased by an amount proportional toL−1(∼&ohgr;−1/2) and both have a quality factorQproportional toL(∼&ohgr;1/2). To leading order inL−1the wave slownesses have the forms2j=s20j[1+(1+i)Mj/L],j=fast or slow, whereMjare combinations of material and geometric parameters. TheQ≡Re(s2)/Im(s2) factors are, for the fast wave,Qfast≊L/Mfast≊L/{[&fgr;&rgr; f/(1−&fgr;)&rgr;−&egr;]} and, for the slow wave,Qslow≊L/Mslow≊L/(1+&egr;). &rgr; fand &rgr; are fluid and solid densities, respectively. &egr; is a usually small parameter given by 2(1−2&ggr;)(&rgr; f/&rgr;)/ [&agr;2pl/&agr;2 f+(1−&fgr;)&rgr; f/&fgr;&rgr;−1], where &ggr; is the square of the ratio of shear velocity to longitudinal velocity in the bulk solid and &agr;plis the velocity of long wavelength extensional plate waves.

ISSN:0003-6951    

DOI:10.1063/1.96994

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Amorphized Si has been irradiated using a 7.5‐ns frequency‐doubled neodymium:yttrium aluminum garnet laser. For low energy density pulses, time‐resolved reflectivity measurements and Rutherford backscattering spectrometry of Cu implantation profiles show that the melted layer solidifies from the surface as well as from the liquid‐solid interface. From interferences in the reflectivity, growth from the surface is found to occur at a velocity of 1.5 m/s. At higher energy densities sufficient to obtain epitaxial regrowth of the amorphous layer, solidification from the surface does not occur.

ISSN:0003-6951    

DOI:10.1063/1.96995

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We present data on a new erasable phase change medium, demonstrating for the first time that very short erase times can be obtained without sacrificing room‐temperature stability of the amorphous state. Thin films of the composition Sb2Se underwent 10% relative reflectivity changes when switched with a laser between amorphous and crystalline states. Twenty milliwatt, 50 ns laser pulses were used for writing amorphous spots; 6.9 mW, 200 ns pulses were used for erasing. A playback carrier to noise ratio of 43 dB was observed on a plastic disk. Amorphous spots could be heated in a microscope to 175 °C before they crystallized. Transmission electron microscopy and x‐ray diffraction indicate that the erased state is single phase and polycrystalline. The crystal structure, however, does not correspond to known compounds in the antimony‐selenium system.

ISSN:0003-6951    

DOI:10.1063/1.97031

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have performed a comprehensive finite element analysis of the diamond anvil cell. Our analysis shows how beveled diamonds and material properties of the gasket affect diamond anvil cell performance. Using the results of the analysis, we have achieved 4.6 Mbar experimentally, which is the highest static pressure reported to date. Possible methods to increase the pressure further are discussed.

ISSN:0003-6951    

DOI:10.1063/1.96996

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Using photoreflectance at room temperature we have evaluated the topographical variations in quantum level transitions of a GaAs/GaAlAs multiple quantum well (220 A˚/150 A˚) due to changes in barrier height and quantum well width. The spatial resolution of the measurement was about 100 &mgr;m. A key feature of our analysis is the ability to fit the electromodulation spectra by a third‐derivative functional form line shape factor. We can detect barrier height changes of several millielectron volts and variations in well width as small as 2 A˚.

ISSN:0003-6951    

DOI:10.1063/1.96997

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Single crystal epitaxial strained‐layer semiconductor‐metal‐semiconductor heterostructures have been grown for the first time. Silicon layers were grown by molecular beam epitaxy over thin (<100 A˚) NiSi2layers on Si(111). The presence of ∼20 A˚ Si template layers formed at low temperature (<500 °C) on the silicide was shown to have a dramatic effect on subsequent Si growth. The overgrown Si layers were rotated 180° with respect to the NiSi2and had a channeling minimum yield of ∼3%. Epitaxial strained‐layer semiconductor‐metal‐semiconductor heterostructures represent a new class of material system with potential for high‐speed device applications.

ISSN:0003-6951    

DOI:10.1063/1.96998

出版商:AIP    

年代:1986

数据来源: AIP