摘要:

The average scattering cross section for reflection of electromagnetic waves by an ensemble of randomly oriented convex particles is calculated. The particles are assumed to be large compared to the incident wavelength and to have a slightly rough surface such that the deviations from a smooth surface are smaller than wavelength. A perturbation expansion resulting from the Rayleigh–Rice approach leads to incoherent and coherent corrections to the zero‐order specularly reflected light. The quantity that in this limit completely determines the scattering behavior of the particles is the two‐point correlation function &rgr;(r) of the roughness structure. The main effect of roughness is a diminution of the reflected intensity for a wide range of the scattering angle &thgr; and a shifting of the maximum of the polarization curve to larger &thgr;. It turns out that measurements of the backscattered intensity in some wavelength limits provide information on the correlation function &rgr;(r). For conducting material, knowledge of the cross‐polarized backscatter intensity over a wide frequency range even enables one, at least in principle, to calculate the complete shape of the correlation function.

ISSN:0021-8979    

DOI:10.1063/1.335428

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A single layer SiO2film with graded porosity applied from a polymer solution derived from organometallic silicon compounds on fused silica lenses provides antireflectivity over the transmission range covering the first, second, and third harmonics of neodymium glass lasers. The damage thresholds of initial samples at 350 nm (3&ohgr;) varied from less than 1 to 9 J/cm2. The main causes of this large variation in the damage threshold were determined to be substrate polishing, substrate surface cleaning, and the coating solution chemistry and processing, which, under certain conditions, leads to carbon formation during the heat treatment of the coating.

ISSN:0021-8979    

DOI:10.1063/1.335505

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A pyroelectric enthalpimetric calorimeter for the H‐O reaction was constructed using Pd and Au electrodes on a 2.5‐cm‐diam, 0.3‐mm‐thick LiTaO3wafer. The counter (or common) electrode was of Au. The detector was placed in a chamber and various gases were admitted at pressures slightly above atmospheric. 100 ppm H2in N2was used as the hydrogen source and pure O2as the oxygen source. A thermal signature was obtained on the Pd electrode that was confirmed by a thermocouple attached to the pyroelectric calorimeter. A delayed thermal signature was observed on the Au electrode resulting from thermal diffusion in the LiTaO3substrate of the heat generated at the Pd electrode. The results on the H‐O reaction are in general agreement with the literature on Pd metal oxide semiconductor (MOS) structures. The results demonstrate the utility of the pyroelectric calorimeter.

ISSN:0021-8979    

DOI:10.1063/1.335429

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Resistance change measurements in ytterbium foils, encapsulated in a polymethylmethacrylate matrix and subjected to impact loading (to 25 kbars) and quasi‐static triaxial loading (to 4 kbars), are presented. Two gauge orientations were examined. Residual resistance measurements were obtained for impact experiments. Both sets of experiments confirm the overall validity of the theoretical analysis described in Ref. 5. In particular, the crossover in resistance change‐stress curves, predicted at low stresses, was measured. The present results show that gauge resistance measurements cannot always be uniquely related to a particular matrix stress component. Restricting the use of ytterbium foils to 20 kbars is inferred from the experimental results. The residual resistance data depend on both foil and matrix response. Finally, analysis of the resistance measurements, along the two orientations in the impact experiments, shows that polymethylmethacrylate retains significant material strength to 25 kbars.

ISSN:0021-8979    

DOI:10.1063/1.335430

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We have demonstrated trapping, confinement, acceleration, and dumping of electrons in a betatron which has a geometry similar to the Astron. 76±22 nC were accelerated to 800±100 keV. This corresponds to a circulating electron current of 60 A. The betatron has a 6‐cm orbit radius and is 1 m long. Electrons are injected tangentially from a 70‐kV, 15‐A field emission diode. A toroidal field roughly equal to the betatron field is used.

ISSN:0021-8979    

DOI:10.1063/1.335431

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A theory for stimulated scattering of a laser beam is formulated where the dominant nonlinearity is the ohmic heating of the plasma. The analysis is carried out with particular reference to experimental investigations of CO2laser heating of a linear discharge plasma. In the conditions characterizing this experiment local heat conduction is of little importance and the dynamic evolution for the electron temperature is dominated by heating and energy exchange with the ion component. These features are incorporated in the analysis. The resulting set of equations gives a growth rate and characteristic scale size for the filaments, which agrees well with the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.335432

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new approach to prepare thin films in a pulsed inductive silane discharge is attemped. The time‐resolved spectral lines qualitatively clarified dynamics of decomposition process in the pulsed silane discharge and the local thermodynamic equilibrium in this discharge was investigated by the population density distribution estimated from excitation temperature measurement. The films had peculiar deposition patterns with good adhesion due to electromagnetic effects and main group of infrared spectra was the SiH3complex.

ISSN:0021-8979    

DOI:10.1063/1.335433

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Plasma arcs in large diameter (d>1 cm) xenon flashlamps often do not completely fill the bore of the discharge tube. The arc is usually initiated on one side of the discharge tube, adjacent to the ground plane, and the fraction of the discharge tube filled with plasma varies as a function of axial location. A model is presented that describes, from first principles, arc expansion in xenon flashlamps. The model simultaneously solves a coupled set of one‐dimensional transport equations in different regions of the discharge tube to simulate two‐dimensional effects in hydrodynamics, electron kinetics, and radiation transport. Using this method, expansion of arcs initiated at arbitrary locations within the discharge tube can be studied. Arc filling fractions are found to decrease with increasing filling pressure of xenon, increasing diameter of the discharge tube, and decreasing stored energy in the discharge circuit. The arc filling fraction also decreases as the breakdown filament moves away from the axis of the discharge tube and towards the wall. Arc expansion is slowed and ultimately halted by a loweredE/N(electric field/gas density) in the gas exterior to the arc, rapid conversion of atomic ions to molecular ions and their subsequent recombination, and by the efficient manner in which radiation dissipates energy which might otherwise be available for thermodynamic expansion of the arc. The asymmetric expansion of the plasma arc results in asymmetric heating of the inside wall of the discharge tube, also calculated in the model. The growth of the plasma arc is also found to be in part responsible for changes in the spectrum of radiation emitted from the arc for various angles of observation. This effect results from wavelength‐dependent absorption coefficients in the plasma.

ISSN:0021-8979    

DOI:10.1063/1.335434

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

It is shown here that the late hydrodynamic effects of fast spark discharges (dI/dt‖t=0≥1010A/sec), i.e., after the discharge period, can be described by a point explosion simulation. The solution is not self‐similar since counterpressure has to be taken into consideration. This non‐self‐similar model is confirmed experimentally by shock wave position and velocity measurements.

ISSN:0021-8979    

DOI:10.1063/1.335435

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A common field distortion triggered spark gap utilizing geometric field enhancement at sharp edges usually operates in a cascade mode via the trigger electrode. A new trigger concept is proposed allowing strong field enhancement and direct breakdown between the two main electrodes. A test setup was designed to prove the feasibility of this concept. Experimental results on delay and jitter depending on percent breakdown voltage are presented. Best results achieved are a delay of 9 ns and a jitter of 2 ns at a self‐breakdown voltage of 15 kV.

ISSN:0021-8979    

DOI:10.1063/1.335436

出版商:AIP    

年代:1985

数据来源: AIP