摘要:

The interaction of continuous CO2laser radiation with water is described. Tightly focused radiation at powers of up to 120 W is used to generate and maintain a conical depression in the water surface similar to the keyhole created during laser penetration welding. The observed penetration depth of up to 7 mm is explained in terms of a hydrodynamic model and observations on the interaction induced liquid flows are described. The momentum reaction to the flow of steam up out of the keyhole generates a downward flow in the liquid around the keyhole with a velocity of ∼20 cm/s under the conditions of these experiments. The experiment has also been performed under variable gravity conditions provided by the NASA KC‐135 Microgravity Aircraft to observe effects associated with changes in hydrostatic pressure and buoyancy on the system.

ISSN:0021-8979    

DOI:10.1063/1.350404

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Results of research conducted on interaction of high‐intensity ultraviolet pulsed KrF laser radiation with a metallic filament in atmospheric air are reported. Experimental results are presented on the time dependent material ejection dynamics associated with pulsed single shot focused excimer laser beams interacting with a small diameter wire. Copper wire 75 &mgr;m in diameter was illuminated with a KrF (&lgr;=248 nm, pulse duration =17 ns full width at half‐maximum) excimer laser at an irradiance of 80 GW/cm2. Interaction dynamics were recorded using both real‐time and double‐strobed ultraviolet laser imaging techniques. Temporal and spatial evolutions of both vaporized and molten material are reported. Material observed, during two‐dimensional shadow imaging, on the side opposite the incident beam (shadow side) was shown to originate from the front ablating surface without spallation of material on the shadow surface. Several spatial material emission velocities are reported utilizing two different imaging techniques. A maximum velocity of 1500 m/s was obtained for material ejected in a direction toward the ablating laser.

ISSN:0021-8979    

DOI:10.1063/1.350405

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A general equation is derived for x‐ray diffractors with arbitrary toroidally curved surface and planes when used with a point source. This equation, which gives the locus of points on a curved diffractor’s surface for a given deviation from the Bragg angle, is shown to yield the appropriate equations for all of the crystal diffractor geometries that were previously discussed by Wittry and Sun [J. Appl. Phys.67, 1633 (1990)]. Two examples are given of the use of the general equation to design diffractors with improved collection solid angle over a range of Bragg angles. The x‐ray collection solid angle and focusing properties of these two examples are given.

ISSN:0021-8979    

DOI:10.1063/1.350406

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In this paper, the complex image method is used to model ground electrodes in layered soils. The image locations and amplitudes are determined through a simple Prony method [R. W. Hamming,NumericalMethodsforScientistsandEngineers(Dover, New York, 1973), pp. 620–622]. As an example, a toroidal electrode in a four‐layer soil is modeled usingonereal image andfourcomplex images. The results obtained are identical to those reported recently in the literature, given by more than 10 000 images using the conventional electrostatic image method.

ISSN:0021-8979    

DOI:10.1063/1.350407

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The induced charge on a grounded arbitrary conductor, excited by a nearby point charge, is shown to be approximated by that on an equivalent conducting sphere near the same point charge. The proof is modified from that for capacitance by Payne and Weinberger [J. Math. Phys.33, 291 (1955)]. A number of examples for different grounded blocks and plate are given. The potential field distributions from the induced charge are also given.  

ISSN:0021-8979    

DOI:10.1063/1.350408

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A drift mechanism of holographic recording in bipolar photorefractive sillenites is discussed. The influence of the external field on the parameters of the ‘‘fixed’’ hologram is presented.  

ISSN:0021-8979    

DOI:10.1063/1.350409

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We use developed high‐sensitivity photoacoustic cell to determine the absorption coefficient in crystals of pure LiNbO3, Mg‐doped LiNbO3, Fe‐doped LiNbO3, KH2PO4, and KD2PO4at the wavelengths of 1060.0, 632.8, 514.5, 488.0 nm. The experimental results are in good agreement with those measured by the laser calorimetric method.

ISSN:0021-8979    

DOI:10.1063/1.350410

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Silicon dioxide films have been prepared by ArF pulsed‐laser ablation of a silicon monoxide (SiO) target in oxygen atmosphere at various substrate temperatures (20–450 °C). The structural and electrical properties of the SiO2deposited films have been investigated. The experimental results indicate a strong reduction of the porosity and structural defects in the films for increasing values of the deposition temperature. Film properties are also strongly influenced by the application of post rapid thermal (400–1000 °C) treatments in Ar atmosphere. The refractive index of these films increases, whereas we observe a reduction of their relative dielectric constant which is mainly attributed to the diminution of the amount of hydrogen trapped into the laser grown oxide. A minimum oxide charge density of 1.5×1011cm−2with a dielectric breakdown field of 2–8 MV/cm was measured in oxide films deposited at 20 °C and subsequently annealed at 1000 °C by rapid thermal treatment (30 s).

ISSN:0021-8979    

DOI:10.1063/1.350411

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Piezoelectric semiconductors such as GaAs are of interest for signal processing devices due to the possibility of monolithic integration of surface‐acoustic‐wave (SAW) ‐based devices and active electronic circuits on the same substrate. The common crystal orientation of GaAs for these applications has been the {100} cut. In this paper the characteristics of surface wave propagation in the {110} plane of GaAs, which supports both the Rayleigh and the Bleustein–Gulyaev surface wave modes, are investigated. Several test devices have been fabricated and studied using laser probe andS‐parameter measurement techniques. The SAW velocity, attenuation, piezoelectric coupling constant, slowness surface, beam profile, and the transducer characteristics have been measured, and the experimental results agree well with the theoretical calculations for both types of the surface wave modes.

ISSN:0021-8979    

DOI:10.1063/1.350412

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In an air‐filled porous medium, the slow acoustic mode may potentially be a useful probe of the geometrical properties of the rigid frame. Use of the acoustic slow wave for probing a two‐component granular system is studied. In a mixture of two granule types of disparate size, experimental results show that the slow wave velocity depends sensitively upon the relative concentrations of the two types of granules. This may be reasonably interpreted as resulting from the varying tortuosity associated with the pores of the granular mixture, with change in relative concentration. From the experiment described, it is concluded that the acoustic slow wave measurement may be used as a sensitive, noninvasive probe of relative concentration in such a multicomponent system.

ISSN:0021-8979    

DOI:10.1063/1.350413

出版商:AIP    

年代:1992

数据来源: AIP