摘要:

By laser beam scanning the optoacoustic signal as a function of the sample coordinates is obtained. Examples for surface and subsurface imaging and for image contrasting are presented.

ISSN:0021-8979    

DOI:10.1063/1.328207

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The waveguide properties of a thin film separating two elastic half‐spaces possessing a shear modulus higher than the shear modulus of the film are investigated. It is shown analytically and experimentally that such a film is capable of localizing the energy of elastic waves near the interface. The velocity of the interface wave is determined by shear modulus, density, thickness of the film, and by the elastic properties of the substrates. The velocity of the interface wave lies between that of the Rayleigh and that of the shear waves in the solid half‐spaces. It is shown that the interface wave can be used to estimate the elastic and dissipation properties of thin interface layers.

ISSN:0021-8979    

DOI:10.1063/1.328208

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The nonlinear diffusion equation has been solved numerically to examine the effects of the temperature dependences of the heat capacity and the thermal conductivity on the variation of temperature with time in heat‐pulse experiments. A range of dependences, simulating amorphous and crystalline insulators at low temperatures, and a range of temperature throws up to 25% have been used in the calculations. It is found that the use of the ordinary diffusion equation may introduce errors of up to 10% for throws of 10%. The effects are particularly noticeable if the thermometer is relatively close to the heater, and resemble those observed in recent low‐temperature experiments.

ISSN:0021-8979    

DOI:10.1063/1.328209

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Capillary oscillations on modulated liquid jets have been investigated using laser illumination and electronic detection of the magnified jet shadow. The amplitudes of several wave harmonics of a growing spatial instability were measured as a function of distance from the orifice for a range of jet velocities and initial‐disturbance amplitudes. The experimentally determined growth rates at the fundamental frequency are compared with theories of capillary‐wave propagation. An empirically derived explanation of the suppression of satellite formation is given. Experimental evidence for infinite‐wavelength capillary oscillations is reported; a description of these oscillations in terms of the Rayleigh theory is presented.

ISSN:0021-8979    

DOI:10.1063/1.328210

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper treats the problem of electromagnetic radiation from the electric and magnetic line sources embedded in a uniaxially anisotropic dielectric or plasma half‐space backed by a finitely conducting medium. The anisotropy of the uniaxial medium is taken along thexdirection and the line source is aligned parallel with thezaxis. For the envisaged geometry,EandHmodes are independently excited by a magnetic and an electric line source, respectively. Expressions for the far‐zone radiation field and the radiation pattern are obtained via the saddle‐point technique of integration. It is noted that the radiation from an electric line source remains unaffected by the anisotropy of the medium and possesses only a radial component of the Poynting vector. In contrast, the radiation from a magnetic line source not only depends on the anisotropy of the medium but has, in addition to the radial component, a circumferential component of the Poynting vector indicating deviation of the resultant energy flow from the radial direction. Numerical results for the radiation pattern and also for the angle of deviation of the power flow from the radial direction, for the magnetic line source, are presented for a wide range of parameters characterizing the anisotropy of the uniaxial medium, the location of the line source, electron‐plasma density, and the conductivity of the half‐space backing the uniaxial medium. It is revealed that in the case of a uniaxial plasma or dielectric backed by a perfect conductor, the radiation has a finite strength of unity both in directions &Vthgr;=0 and &Vthgr;=&pgr;, in contrast to the case of a medium backed by a finitely conducting medium.

ISSN:0021-8979    

DOI:10.1063/1.328211

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Results of a hydrodynamic computer code are presented, which describes the expansion of a laser generated plasma into an ambient gas. The theoretical model includes diffusion, thermal conduction, elastic collision interaction and the detailed kinetics of excited atomic and ionic levels. The retarded plasma motion results in a slow electron density decay. Effective electron cooling is achieved in the diffusion region where the plasma mixes with the background gas. Quasisteady‐state population inversions occur in the resulting cold and dense plasma.

ISSN:0021-8979    

DOI:10.1063/1.328212

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Transport equations for mass, momentum, energy, and heat flux based on the thirteen‐momentum approximation of the Boltzmann equation are analyzed in the isobaric approximation. The left‐hand‐side terms are estimated and compared with terms representing the collisional transfer for the transient case of nonequilibrium two‐temperature discharges in monoatomic gases. A simplified form of the equations is derived and the corresponding conditions are expressed as functions of the physical properties of the plasma. The system of equations is solved for a 0.5‐A argon discharge at atmospheric pressure. The arbitrary initial distributions are allowed to relax to the equilibrium state, which is compared to previous results for a 0.4‐A free‐burning discharge in argon.

ISSN:0021-8979    

DOI:10.1063/1.328213

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

One of the problems in the understanding and implementation of the plasma etching process is the general lack of quantitative information about the effect of the many process parameters involved. We have been studying the effect of gas flow rates in the etching of silicon materials in fluorocarbon gases, and have been led to define a utilization factor to describe the extent to which the reaction gas is converted to volatile products of the plasma etching process. The experimental evidence for the importance of a utilization factor in plasma etching is shown, and some of the surprisingly many ways in which flow rates influence the whole etching process are illustrated.

ISSN:0021-8979    

DOI:10.1063/1.328214

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The flux of backstream electrons to the source plasma region increases significantly with the acceleration voltage of an ion beam, so that the back plate in the arc chamber should be broken for quasi‐dc operation. The flux of backstream electrons is estimated at the acceleration voltage of 50–100 kV for a proton beam with the aid of ion beam simulation code. The power flux of backstream electrons is up to about 7% of the total beam output at the acceleration voltage of 75 kV. It is pointed out that the conventional ion sources such as the duoPIGatron or the bucket source which use a magnetic field for source plasma production are not suitable for quasi‐dc and high‐energy ion sources, because the surface heat flux of the back plate is increased by the focusing of backstream electrons and the removal of it is quite difficult. A new ion sourc which has an electron beam dump in the arc chamber is proposed.

ISSN:0021-8979    

DOI:10.1063/1.328141

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Superelastic laser energy conversion has been shown to be capable of extremely rapid rates of plasma heating with relatively modest values of laser irradiance. In the case of a boron III plasma,dTe/dt≳1013 °K sec−1has been predicted for a initial boron III ion density of 1017cm−3. The laser irradiance needed to achieve this rate of change of the free‐electron temperature is about 5×108W cm−2per cm of path length.

ISSN:0021-8979    

DOI:10.1063/1.328142

出版商:AIP    

年代:1980

数据来源: AIP